This blog is partly a re-creation of our original house self-build blog from the now defunct Ebuild forum and also a means for me to present a commercial-free view of the process of self-building and some of the many challenges it presents.

First a word of caution, though.   It is with great reluctance that I have to bring to the attention of anyone reading this blog, or looking at the images here, that an Irish Company, Viking House, is using some copyright images of our house build, some which are on this blog, for advertising purposes on at least two of their websites, together with false and misleading information about our build.  We have never had any contractual arrangement  with Viking House, or with the gentleman who runs it, Seamus O’Loughlin.

I would very strongly recommend that anyone thinking of doing business with Seamus O’Loughlin think carefully and do some proper background checks before doing so.  We are heartily sick and tired of meeting, and hearing of, people who have been disappointed, misled or just confused by him.  We are about to commence legal proceedings against him, for both copyright breach and misrepresentation.  He has refused to remove images that are my copyright from his website and has also refused to correct the significant errors in his description of our house, errors that are a consequence of the fact that the house wasn’t built by him, his company, or any company  that he controlled.

For clarity, I have granted a licence to use images to several of our suppliers, some of whom use them in their advertising material with our full consent.

Back to this blog.  I started writing this a week or so after Ebuild went down.  Given the susceptibility of forum-hosted blogs to disappear at very short notice if a forum goes down (as happened with Ebuild), I, and one or two other former Ebuild members, thought it sensible to have a record of our build that was under direct, personal control, and properly backed up locally in case something failed (this is backed up every night locally to a Raspberry Pi, that’s running a LAMP stack and WordPress, believe it or not!).

This is the only copy of this blog that is maintained and where comments will be replied to.

Feel free to comment, but please no commercial content or use of user names that are related to a commercial enterprise.  I will only edit content that is either in breach of copyright, is unlawful or is, in my view, aimed at promoting someone’s own business interests, as this is a strictly not-for-profit, resource for self-builders.



Domestic electrical installation earthing and circuit protection – part 2

In part 1, I left the tale at the point where the DNO had provided a supply to the premises, most probably with a TN-C-S earthing scheme for a new build.  For the purposes of this article, I’ll assume you have been provided with a supply capable of running a TN-C-S earthing scheme, and that the incoming supply looks something like the diagram below, once the house is completed:

In the first part, I mentioned the breakdown of ownership and responsibilities within the meter box, and how they would be different if you had a TT earthing scheme.  Taking the ownership thing a bit further, you own the meter box and are responsible for ensuring that it is of the correct type, is located so that it is easily accessible by your electricity supplier and that it is is securely fitted into a structure, like a wall or other strong enclosure.  It’s worth noting that meter boxes are to a standard design, and frankly a lot of of them aren’t that weatherproof.  They are just good enough to keep the interior dry if mounted in a relatively sheltered location.  I’ve heard tales of them being located in exposed locations and rain being driven in through the door edges and pooling in the bottom  The door hinges are not that robust on some of the cheaper ones either, so my personal view is that it’s a good idea to get a good a quality box as you can and fit it in a fairly sheltered location.

The DNO will normally want to install the incoming cable through the hockey stick conduit you normally provide (sometimes they will provide it, but you can’t always rely on this), in the left lower corner of the box, with their sealed box, that terminates their cable and provides the location for their 100A fuse*.  This termination unit, often referred to as the “head”, or just the “company fuse”,  provides terminals at the top for the Line and Neutral tails to the meter and a terminal at the side for the earth conductor connection (except if your supply is TT).  The electricity supply company you’ve chosen (unlike the DNO, this can be any supply company that offers a supply in your area) will arrange to come and install their meter in the box, usually above and slightly to the right of the incoming cable termination.  Before they come, ideally you need to put in place the consumer-side equipment, so that they can also connect your Line and Neutral tails to the meter and seal the connections.

Some suppliers are now switching to using meters with an isolating switch built in (usually operated via a screwdriver slot) and an unsealed access cover to the consumer-side terminals.  This is a big advantage, as it allows your electrician (or yourself, if a “competent person”) to isolate the supply and connect the consumer-side up later, as only the supply side terminals have a sealed cover.  It goes without saying that only the DNO or the electricity supplier have the authority to break the seals and access these connections, neither you, nor your electrician, are allowed to break these seals.  This is, I have to say, a rule that is observed as much by the times it’s broken as by the times it’s observed, in practice, but nevertheless, if you find a broken seal on the DNO termination then you should report it to them as quickly as possible and the same with the electricity supplier if the meter seal is broken.  The reason for quick reporting is that, quite often, broken seals are taken as evidence of tampering, usually with intent to steal electricity from the un-metered side of the supply.  It’s also bloody dangerous working on live part of the installation unless you have the proven competence and equipment to so so, so these parts should be sealed so that they cannot be accidentally uncovered.

The tails (the short sections of heavy duty conductor that make the Line and Neutral connections within the meter box) are your responsibility (from the meter) and must be double insulated, with a blue inner sheath for the Neutral and a brown inner sheath for the Line.  The outer sheath will often be grey.  To show which conductor is which, the Line should have a brown or red sleeve or bit of tape around it, and the  Neutral should have a blue or black sleeve or bit of tape around it.  They can be tagged or labelled “N” and “L” instead of using colour coded tape or sleeves, but often they are left unmarked.  If in doubt, the normal sequence of connections at the meter is that the left outer connection is the Line in from the DNO fuse, the left centre is the Neutral from the DNO termination box, the right centre connection is the Neutral to the consumer side and the connection to the right is the Line to the consumer side.

The Line and Neutral tails should be 25mm² in cross sectional area, and must be no longer than 3m from the meter termination to the Consumer Unit or fused isolating switch.  The Earth conductor should have a green and yellow striped sheath and be 16mm² in cross sectional area, and should normally terminate either to the Consumer Unit, or to an earth block, to which all other earth connections can be made.

With a new supply for a self-build, then you have two initial choices.  You can ask (and pay) for a Temporary Site Supply to be installed.  You provide the cabinet, consumer side equipment for the site supply and the earth rod, as all temporary site supplies have to be TT earthed – it’s the DNO rules.  The consumer side of the temporary site supply needs to be signed off by a competent person, to keep your site workers safe, to comply with the regs and to keep your site insurer happy.

Alternatively, you can do as I, and others have done, and decide to have a permanent domestic supply installed on site, before the foundations or house is built, that happens to have an external socket as a site supply.  This way you avoid having to pay the DNO twice, as all future changes are on the consumer side, and none of their business.  To do this you have to erect a structure in which to fit a standard meter box.  In our case I needed a fence to screen the place where the wheelie bins were going to go, as originally we had to comply with the Code for Sustainable Homes, and that required a recycling bin storage area, and because we’re inside an AONB and adjacent to a Grade II listed building, the planners demand that all wheelie bin storage areas in new builds must be screened from the road.  By a mixture of luck and design, we managed to locate a thick, box-like, fence, over the top of a big three phase DNO underground cable that we had relocated as a part of the site preparation.  There was no recorded wayleave or easement for this cable in its original location (diagonally right across the site, see the second photo in this blog entry: http://www.mayfly.eu/2013/06/part-five-trials-and-tribulations/ ), so technically the DNO had no right to have run it under the site anyway.  When we wanted it moved we came to an arrangement with them to put it exactly where we wanted it to go, right along our boundary (well, about a metre inside it for safety) and right under where I planned to fit the meter box.

The reasons for wanting the meter box very close to this big supply cable were two fold.  Firstly, I wanted the possible option of being able to have a 3 phase supply in the future, as I have machine tools in the workshop and generally buying second hand 3 phase tools is a lot cheaper than buying single phase ones, and they tend to be a bit beefier.  As it happens I don’t think I’ll ever bother to do this now, I’ve had enough hassle with services!

The second reason was to do with our planned PV panel installation.  I wanted to exceed the 3.68 kWp limit that applies to an installation that doesn’t need DNO permission, and so wanted as good (in terms of low impedance) connection to the local distribution network as possible.  Being over the three phase cable also meant that if the DNO refused a request for more than 3.68 kWp, then I could have a second phase installed, and that would allow  me to fit two 3.68 kWp PV systems, each to a separate phase, without needing DNO permission.  In the end they granted permission for a single 6.25 kWp PV installation on a single phase supply, which was good news, as it was cheaper all-round.

Getting back to the initial installation, if you do as I did and fit a permanent domestic supply from the start, then there are several things you need to look out for.  Firstly, as mentioned above, even though this is a permanent domestic supply, the DNO rules say that you must not connect the Earth to their PEN terminal.  It doesn’t make any sense at all in this scenario, but they are adamant that, until the house is erected, you must use a TT earthing scheme.  Their rule makes perfect sense for a true temporary site supply, but none at all for a properly wired permanent supply that just happens to exist on a site without a house.

So you will need to put in an earth rod, as close as practical to the meter box (being aware of the location of any underground cables or pipes), connect a 16mm² green and yellow sheathed Earth wire to this, with the proper clamp, protect the termination at the top of the Earth rod with a green plastic protection box and protect any exposed length of Earth conductor by putting it within conduit, secured to the green plastic box.  This Earth conductor needs to be terminated in the meter cabinet to an earth block, where the other Earth conductors can also be connected.  This Earth also needs to be tested, to ensure that it is under the normal maximum allowable impedance of 0.8 ohms.

The next point to watch is one I made earlier.  Under the regs, you are only allowed to run three metres of conductor tails from the meter to the main switch in your consumer unit or other form of isolating switch.  In our case, or the case of anyone who chooses to locate their meter box away from their house as we have done, then the tails from the meter need to terminate in a fused DP isolating switch, ideally with a fuse that’s rated at a slightly lower value than the 100A* company fuse.  For example, I fitted a DP fused isolating switch with an 80A fuse in the upper right corner of our meter box, and that then connects to the three core length of 25mm² SWA (Steel Wire, Armoured) cable that runs in a duct under the house and up through the floor and wall service space to our services room, where it is terminated properly in a metal box, with 25mm² Line and Neutral tails and a 16mm² Earth tail.

As an aside, getting hold of three core SWA with the correct core colours isn’t that easy, as it normally comes with three phase core colours.  Having the wrong core colours isn’t a problem, but does mean that the sheaths around the internal cable ends need to be sleeved or taped with the correct colours.  I managed to find a supplier of three core 25mm² SWA that had brown, blue and green/yellow cores, for pretty much the same price as the more common three phase stuff (which has brown, black and grey cores), which made for a neater looking installation (not that you can see it under the covers!).

Because I wanted to keep the house supply, fed from the SWA cable mentioned above, separate from the supplies feeding the borehole pump, the sewage treatment plant, an external 16A Commando socket (as a site temporary power connection) and the garage, which was to be used as a workshop, I terminated the tails from the meter to a Henly block and then fed separate short tails to the fused isolating switch for the house and a small Consumer Unit that contains two 40A, C curve, DP MCBs.  This small Consumer Unit protects, and provides a means of isolating, the 6mm² SWA that runs inside the meter fence for a short distance to a waterproof (IP68) four way Consumer Unit, that houses four DP RCBOs.  The second 40A DP MCB feeds and protects the garage/workshop 6mm² SWA supply cable.

As an aside, I mentioned these were “C curve” MCBs.  This means they have a slower trip time when overloaded, more of which later when I get to describing the garage supply itself, but it’s useful to be able to provide adequate cable protection without over-sensitivity that might cause nuisance tripping.

This means that, from the meter cabinet the house supply can be isolated without affecting the external supplies, and if there is a need to work on the waterproof Consumer Unit, then it can be isolated using the DP MCB in the small consumer unit and also the garage supply can be isolated from the meter box using its DP MCB.

This diagram shows the consumer-side wiring inside the meter box, with the supply from the meter, in the TT configuration that’s required for the temporary site supply (this was changed later to a TN-C-S connection, after the house electrical installation is completed):

The important thing to note here is the way each outgoing cable and circuit is protected.  For example, the cable feeding the waterproof Consumer Unit, that supplies all the external power feeds, is protected by the 40A DP MCB, from current overload.  That cable is capable of safely carrying over 60A, so is adequately protected against an over-current fault by that MCB.  Having a DP MCB as an isolating switch allows the external electrical installations fed from the waterproof consumer unit to be isolated from a single point, without affecting the supply to the house.  It’s acceptable to use a DP MCB as an isolating switch in this application.

Similarly, the 6mm SWA cable feeding the garage is protected by another 40A DP MCB that allows the garage supply to be isolated and which protects the cable under slow overload conditions.  The latter point is significant, as it’s best to try and stage overload trips so that the most sensitive device is nearest the end user, in my view.  For this reason, C curve DP MCBs were used at the meter box end, as they are slower to respond than the more normal B curve units.  At the garage end, there is a B curve RCBO that should trip faster in the event of an overload than the cable protection DP MCB.

In the same way, the 80A fused isolating switch protects the 25mm² three core SWA cable that feed the house from an over-current fault, and also allows the house supply to be isolated whilst maintaining power to the external electrical circuits.  This isolating switch also has the capability to be locked, using a small metal device and a small padlock.  This was to ensure that, when the external electrical circuits were live, to provide water, sewage treatment and site temporary power, via the 16A Commando Socket, the house supply could be locked off, with the key to the isolating switch kept by the electrician working in the house.  Whilst not completely foolproof, this provided a safe enough method of working for those working in the house, whilst we still had live circuits elsewhere on site.

The diagram below shows the waterproof consumer unit, that has four, DP RCBOs.  The reason for fitting DP RCBOs in this box was to provide both over-current protection on the (mainly) underground cables and to provide protection from earth leakage faults as well.  This was particularly important during the time when the 16A Commando socket was being used as the temporary site supply, as it provided a reasonably high level of fault protection to any cable plugged into that socket.  It proved itself when one contractor tried to use a small submersible pump, to drain a trench, which tripped the RCBO.  I checked his pump and it clearly had an internal fault that was making the case live!  The chap had been using it for a fair time, and said this was the first time he’d had a problem, but added that he usually used it with his own generator, which probably didn’t have adequate protection on the output, and which he admitted he never earthed with a rod, either.

Two of the other circuits running from this Consumer Unit are running to wet areas, one from a 10A DP RCBO feed runs to the sewage treatment plant, the other, with a 20A DP RCBO runs to the borehole pump.  The third circuit is another 6A DP RCBO that feeds power to the energy metering and excess PV power diversion system, mounted in an IP68 waterproof box adjacent to the meter cabinet.  The fourth circuit in this box is a 16A DP RCBO that feeds the front panel mounted Commando socket, for site power.

Since completing the house, the Commando socket has been disconnected and this 16A feed now runs via a length of 2.5mm² SWA to one of my electric car charge points, at the end of the drive nearest the house.  This is only a 15A charge point, and so using 2.5mm² is over-kill – it happens to be a bit of cable I had left over from wiring the borehole pump.  Electric vehicle charge points must have double pole residual current/earth leakage protection, as defined in J1772 and the IET Code of Practice  for EVSE installations (as far as I know, they are not yet included in the wiring regs, BS7671, or they weren’t at the time of my installation).

The garage supply is slightly different, in that the length of 6mm² two core SWA that feeds the garage does not also supply the garage protective Earth.  The garage runs on its own TT earth system.    The reason for this has more to do with my personal view about Earth protection in what will often be used as a workshop, with machine tools, than anything else.  It would have been perfectly OK under the regs to export the earth from this Consumer Unit to the garage, using 3 core SWA, and that would have been simpler to install, too.  The Earth impedance at the garage would have been within limits and the installation would have been considered safe, in regulatory terms.

The concern I had was that I wanted to be near 100% certain that the exported Earth and the concrete floor of the garage were at the same potential, even under very short duration, high instantaneous fault current, conditions.  Running an Earth down a fairly long conductor increases its impedance slightly, and this tends to slow down the operation of RCDs and MCBs a little bit.  I decided that I’d feel more comfortable if I adopted a TT earthing scheme at the garage itself.  To overcome one of the main issues with a TT system, the vulnerability of the Earth rod and connection to damage, I fitted a double length rod (two sections screwed together) through a hole in the concrete slab that was lined with a short length of plastic pipe.  The rod was driven around 2m down into the gault clay subsoil, to a level below the local water table, in order to ensure a low resistance connection to the ground.  Clay is usually reasonably good at ensuring a good contact between the rod and the soil, because of it’s fine soil particles, as long as it’s moist.  In this case, because the lower part of the rod was into clay that was always moist, I was ensured of a good earth.  It turned out to be slightly “better” than the Earth provided by the DNO when tested, which just proved to me that, in this case, using a local Earth for the garage was a sensible move.

There are particular issues that have to be resolved when using a different earthing scheme at one end of a supply like this.  Firstly, the DNO provided Earth needs to be kept separate from the local Earth.  What I did, which was more because of the sequence of doing the external wiring and building the garage and house than anything else, was to connect the incoming SWA, with an external gland, to the base of a plastic IP68 junction box and secure this to the floor of the slab in a corner, right next to the plastic box with the earth rod terminal.  I could do this because the SWA cable coming up through the garage floor was in a 50mm flexible duct, cut flush with the floor.  This allowed the gland to be made off and then the cable pushed back down a few inches to secure the box, maintaining the Earth isolation.  The 6mm² cable feeding the small two way consumer unit in the garage was fed through fixed conduit, with a short length of conduit between the Earth rod box and the IP68 box for the earth conductor.  These conduit connections were made after the garage was erected, when the IP68 box no longer needed to be watertight.

The garage consumer unit has a 40A B curve DP RCBO in place of the main switch, followed by two MCBs to provide over-current protection, a 6A one for a lighting circuit and a 32A one for the garage power ring main.  The diagram below shows how the garage end is wired:

With this TT earth at the garage, it was important to ensure that the Earth rod was both effective, in terms of having a low enough impedance (the regs state it must be under 0.8 ohms) and that it was well-protected from damage or corrosion.  The main downside to having a local TT Earth like this is that you are responsible for ensuring it’s still OK over the years, but really that also applies to any electrical installation, it makes a great deal of sense to undertake regular safety checks, just to ensure everything remains OK.

There are ways of doing DIY  checks on things like the effectiveness of earthing system, the conductivity of earth rods when in the ground, etc, but they require a degree of knowledge to do, plus some basic test equipment.  I won’t describe them here, only because there are risks involved and I wouldn’t wish anyone to follow advice from here and get hurt.  Similarly, all of the information above is given for educational, not practical, purposes.  All of the wiring I’ve described either has to be installed and tested by a “competent person”, or has to be inspected and tested by one, and that inspection involves being able to physically see all of the cables and connections, which in many cases makes DIY wiring impractical.

Finally, as mentioned earlier, under the DNO rules, you have to connect your main supply Earth to an Earth rod (i.e. TT) whilst you are building the house, but as soon as the house is built you are allowed to move your Earth from the Earth rod to the connection provided on the head and have a TN-C-S system.  Why?  I’ve no idea.  Nothing has changed as far as the DNO or the level of risk is concerned, but they have rules, so you must follow them.  As someone with a technical background this rule is illogical under these specific circumstances, but I think it’s down to the “tick box” mentality of the DNOs.   As soon as the house electrical installation is complete and signed off, you (if you are a “competent person”) or your electrician can swap the main 16mm² Earth wire over from the TT earth rod to the TN-C-S Earth connection, usually provided under a small plastic plug or cover on the right hand side of the incoming supply, and marked as the Earth connection point.


*The company fuse should normally be 100A, as this is the standard domestic supply, but you may only be offered a restricted supply, because of local network capacity issues, and I have seen supplies limited to as low as 60A in some rural areas.  This is well worth asking about when you request a new supply from your DNO, as if there is a local capacity limit and you need more power than is being offered, then you maybe asked to pay for the local network upgrade to provide this – which is never cheap!

Downloads from the top menu

Some have asked me for copies of stuff, or links to downloads, and rather than email them out individually I’ve added them to the “downloads” menu at the top of the home page here.

The link to the Stroma FSAP download page is just that, a link.  Stroma offer their SAP software on a free basis, so anyone can use it to do their SAP calculations.  However, only an accredited assessor is allowed to officially submit the reports, so although useful from an educational perspective you have to be aware that the reports that are produced from this free software will be watermarked “DRAFT”*** and will not have an assessors name or registration number on.

The spreadsheets were all written by me to help me get my head around some of the things when I was first designing our house, to allow some “quick and dirty” comparisons of different build methods and also to assist when it came to doing the VAT return at the end (HMRC will accept these printed form replicas without any problem at all, BTW).

All the spreadsheets are free for anyone to use for a self-build, all I ask is that they not be distributed further, or used by anyone, for profit.  My intention is to freely share, not give someone a hand in starting a business on the back of my efforts!  They contain no macros or harmful code that I know of, have been virus scanned and can be trusted to be safe, in as far as I’m able to assure this.

The heat loss calculator has local climate data taken from the Met Office for our specific location.  It’s a bit of a game finding this data on the Met Office website, as they keep changing it, but when I got the data that’s in the copy above it was very local, and was from (I think) the previous ten years of Met Office data for our region (roughly mid-way between Salisbury, Wiltshire and Shaftesbury, Dorset).  You really need to poke around in the Met Office web site and find the data for your area, which as I recall means looking at each month, one at a time, and noting the data down by hand, as there was no easy download that I could find!  Sorry I can’t give a link to where this data is held, but that’s down the Met Office having moved it twice since I wrote that spreadsheet, and any link I gave would almost certainly be out of date soon after I posted it.

The U Value Calculator is again a bit “quick and dirty”, as it takes no account of thermal bridging within a structure and neither does it adjust for varying surface heat transmission.  The outer face of a wall or roof will, for example, have quite a wide variation in surface heat loss rate, and I’ve made no effort to put the surface thermal transmission corrections in to this simple calculator.  It assumes still air both sides and makes no corrections for varying surface emissivity.  This means it will, generally, give a lower (better) U value than the centre of a section with thermal bridging members, but also means that you could have a U value that’s higher (poorer). by perhaps as much as 15%. for a timber frame that has no mitigation against thermal bridging.

Our house is virtually thermal-bridge free, as it uses some clever design features to virtually eliminate all the normal cold bridges you get with a timber framed house, and the passive slab foundation removes the wall/foundation junction heat loss path that a standard form of construction will probably have to some extent.  It’s mainly for this reason that I didn’t take the time to model thermal bridging losses, as they didn’t apply to our particular house build method.


***There is a way to deal with this if all you’re doing is submitting a design SAP, where you don’t need an official assessor to submit the report.  Contact me if you want to know more – it’s what we did and it saved a bit of cash when we submitted our full plans building control application.

Domestic electrical installation earthing and circuit protection – part 1

This is a, rather lengthy (even though it was intended to be brief), bit on the history and background of domestic electricity supply earthing and circuit protection systems, and why they are important, to help understand why we have earthing and circuit protection schemes in the first place, what they are for, how they’ve evolved, and why, together with the expertise of the electricians we employed, I made the choices I did.

Like any history, it’s written from my personal perspective and reflects my view on why certain things were done at certain times.  Much of the reasoning for some of the decision making has been lost, so inevitably some of the historical aspects are a reasonable guess. using information from multiple sources.  The later history is more accurate, as I was indirectly involved with rule making from around the time of harmonisation onwards, specifically with the formulation and application of the LV Directive and the EMC Directive.

This may sound an odd thing to write, but there is NO such thing as a safe electrical installation, and there never can be.  Safety is not a finite entity; no matter how hard we try we cannot remove all of the risk, and some risk ALWAYS remains.  All we can ever do is try to mitigate the remaining risks by a carefully thought-through design, balancing what we personally find acceptable in terms of risk, cost and convenience, with what is within the requirements of the regulations that apply at the time your installation is installed.

This article is not directly related to our build, but it is background that may help explain some aspects of electrical installation design, specifically why we have two different earthing systems on our site, one on the supply side and a different one on one external part of the protected consumer side.  I’ll go into more detail about our external wiring in a later post that addresses that specifically, and gives clear reasons as to why it was done that way, as several people have asked me about it and it seems to have caused some controversy elsewhere amongst the less well-informed.

I’ve decided to write it here, primarily as advice to self-builders, as whether you employ an electrician, or feel competent enough to do your own electrical work (with the appropriate inspection and testing by a competent person), there is information you need, and decisions that you need to make, in order to determine what best fits your own personal balance between safety, risk, cost etc.  There is no “one-size-fits-all” solution, in my opinion.  It is my view that only you will know what risks you are prepared to accept, how much more you are prepared to pay to reduce the risk level further, and what level of inconvenience you will accept.  If you can decide what is acceptable to you, then it goes some way to helping with the overall design of your electrical installation.

You may have some planned future uses for areas that impact on the design of your electrical installation, and rather than just let your electrician decide what to fit based on what you’ve specified now, it’s useful if you know enough about the impact of future plans on the electrical installation so that you, or an electrician, can plan ahead and choose the best solution specifically to meet your anticipated requirements.

Also, although I hate to say it, there are some electricians around who are not as competent, knowledgeable or free-thinking as they should be, so the better informed you are, the more chance you have of getting an installation that is acceptably safe, convenient to use, meets your needs and is within your budget, without the need for later costly modification.

First some definitions, as they may make reading this, and the second part of this article, that will cover circuit protection, a little easier:

Line (sometimes colloquially called “live”) is the power feed wire FROM the supply to the Load.  In simple terms, this is a really dangerous connection in terms of getting an electric shock.

Load is the equipment or device that is using electricity when it is operating.

Neutral is the power return wire FROM the Load to the supply

Earth is the potential of the ground around the Load, but is colloquially used as the term for the wire that protects either the  supply, or the Consumer, by being connected to the ground potential.  It is sometimes referred to as the Protective Earth, however, strictly speaking, these may have either the same, or different, roles, depending on the nature of the system.

Consumer is the generic term for the user of the electricity supply.

Conductor is generally a wire or cable that conducts electricity, but can refer to anything that can conduct electricity, such as a metal case or pipe.

Protective Earth and Neutral (PEN) is the term used when a supply conductor Neutral is also the Protective Earth connection, and may, infrequently in my experience, also be referred as the Combined Neutral and Earth

Fuse or Circuit Breaker or Miniature Circuit Breaker (MCB) is any device that is intended to break or disconnect a circuit whenever the current flowing through that circuit exceed a certain rated value.  In a domestic electrical installation it is there to protect the conductors in the circuit from over-heating, becoming heat damaged or even being a possible cause of fire, nothing more.

Switch is a device for making and breaking one or more ciruits when operated.

Pole refers to any individual and separate electrical supply conductor, and in the context of this article normally refers to either the Line or Neutral

Voltage is the electrical equivalent of pressure in a water system, it is the “force” available to drive a current through a circuit.

Current is the electrical equivalent of the rate of flow of water in a plumbing system.

Potential refers to a voltage difference between two conductors or a conductor and an area, such as the voltage difference between the Line conductor and the local Earth.

Impedance is a measure of the opposition an electrical circuit presents to the initial current flowing through it when a voltage is applied.  It is not the same as resistance.

Resistance is the steady-state opposition an electrical cicruit presents to a steady current flowing though it.  It may well be lower than the impedance in the specific case of measuring domestic electrical installation circuits.

Single Pole (SP) refers to any switching device that only makes and breaks the Line conductor, rather than both the Line and Neutral conductors.

Double Pole (DP) refers to any switching device that makes and breaks both the Line and Neutral conductors at the same time.

Isolator is another term for a specialised type of DP Switch, one that may or may not have additional special  capabilities.

Residual Current Device (RCD) is a device that measures the difference between the current flowing through the Line conductor and that flowing back from the load through the Neutral conductor, and breaking the circuit if there is a difference between these two currents.  A difference indicates that current is “leaking” out of the circuit, so in some countries you will find these devices referred to as Earth Leakage Breakers.  In many ways this is a more accurate description, as the “leaking” current is almost always flowing to Earth.

Residual Circuit Breaker with Overload (RCBO) is a combination device that combines the function of an RCD with an MCB.  In other words, it will break the circuit in the event of either a current overload, or a current imbalance between Line and Neutral.

There are many other terms, but I’ll try and keep this as simple as I can, and define any thing else as I go along.

A Much Simplfied History Of Domestic Wiring Development

Years ago, when we first had electricity supplies in homes, we had no earthing or circuit protection systems at all, power was distributed around a house most commonly by two core cable  and two pin sockets and one of the two pins was usually close to earth potential, because it was connected to the earth (literally)  back at the power station or substation, or even at the house battery pack or generator in some cases.  Inevitably there were deaths and injuries from this system.  Plugs could be inserted either way around,  a broken connection or lead could make an appliance case live and create an electric shock hazard and wiring wasn’t protected from overload, could over heat and start fires.  As most appliances were made of, or contained exposed, metal parts, the electric shock risk was very real.

To make things worse, plugs and sockets weren’t to any particular standard, they varied from one manufacturer to another.  Between the wars, standards were first created, and one of the first things that were standardised were the dimensions of 2 pin plugs.  Standardising plugs didn’t address the safety issues but it did mark the effective beginning of the document that we still rely on as the “bible” of electrical safety, by creating the first electrical system regulations.

As soon as the use of electricity became fairly widespread, it was clear that there was a significant risk of electric shock from the two pin system.  The plug  standard was changed to a 3 pin design for higher power appliances, still with round pins, but with the third, larger and longer, pin being connected to earth.  Lower power appliances continued to use two pin plugs, and two core cables, for many years, despite the greater risk of electric shock.  At the time that three pin plugs were introduced, it wasn’t usual for there to be an earth connection provided on the incoming supply cable to a house, just a line and a neutral, or a positive and negative on DC household supplies, as at that time we had a mix of supply types and voltages.  Some were Alternating Current (AC) and some were Direct Current (DC) and the supply voltage varied, too.  The system you had depended on where you lived, as each supplier tended to have a slightly different system.

Although the neutral in an AC supply (or either one of the two terminals in a DC supply) at this time was usually close to earth potential, it could well have been connected to that earth a long way away, so have a fairly high impedance compared to the local earth.  Impedance is important, as it determines the “instant resistance” of the cable when a fault current starts to flow through it, and may well be higher than the steady resistance of the same cable when the current has been flowing for some time.  This is down to some detail I won’t go into here, but suffice to say that, when a fault occurs you want that initial resistance to earth to be as low as possible, so high fault currents can quickly be conducted to earth, without increasing the potential (voltage above local earth in this case) of the faulty appliance parts that can be touched, to a dangerous level.

When three pin plugs were introduced, they needed an earth connection for safety, but generally no such connection was provided with the electricity supply.  This meant that the earth connection had to be created, either locally, or by a third conductor provided by the electricity supplier.  Interestingly, this connection gets its name from the way it made, the earth conductor, wherever it happens to be located, is physically connected by a conductor to a rod or plate that was buried in the earth outside, so it was, originally, literally a connection to the earth.  The idea was that exposed metals parts, or the metal case, of every electrical appliance would be connected to this earth terminal through the third earth pin on the plug and because this terminal was close to the same potential as the floor the person was standing on the risk of electric shock was very much reduced.

For example, say someone was using an electric iron and was standing on a flagstone floor, when the iron developed a fault, say a frayed cable that was touching the case or handle inside the iron.  With a two pin system there was a near-certain risk that the person using it would get an electric shock, because the current could only pass from the live case of the iron to the persons hand and then through their body to the ground they were standing on, in order to get to the earth beneath.  With the three pin system, by connecting an earth cable to the case of the iron, the fault current would rather flow through the lower impedance earth cable, to the external earth connection, than through the much higher impedance of the person holding the iron, so greatly reducing the risk of electric shock.

One consequence of adopting this system, was that fault currents through the wiring and earth cable under a scenario described above, could be very high, high enough to overheat the wiring and perhaps start a fire.  So, one risk had been reduced, but another made significantly greater.  The risk of fault currents over heating a conductor had previously only been from the line and neutral, or positive and negative, conductors touching, or shorting out, so earthing introduced an additional conductor overload risk.  This risk was mitigated by adding a fuse into each circuit in the house.  This fuse was only there to protect the cable in the house, an important  principle that still applies today in a domestic electrical installation, even though we’ve mainly replaced fuses with different types of over-current protection devices in our fixed wiring today.

For decades this three pin plug system worked well, but there were still hazards with it.  Although the plugs were now a standard size, the same wasn’t true for the design of sockets, and most did not include any means of preventing something being poked into the line connection, giving that person a potentially lethal shock.  Also, there was no specific fuse protection for the flexible lead from the plug to the appliance, as the fuse protecting the house wiring would usually be rated to blow at a much greater current than the thin bit of flexible cable connecting something like a bedside light.  We also still had two pin plugs and two core cables for low power loads, like lights, and so there was still an electric shock risk from those.

Around WWII, a new “universal” standard of plug was introduced, that corrected both these failings, and a standard was also made for the front face of sockets, to add further protection to consumers.  This lead directly to the plugs and sockets we use today, those made to BS1363.  They overcame the need to protect the appliance cable from over load by having the facility to fit a small fuse inside the plug.  They also reduced the risk of a young child poking something conductive into the line connection, by having a shutter that blocks the line and neutral, and which is opened by the longer earth pin being inserted.  The longer Earth pin also meant that the Line or Neutral side of the circuit would be broken first, if the plug was pulled out, leaving the appliance earthed right up the the point where the plug was fully removed from the socket.  This is probably still one of the safest domestic electrical connectors around, especially now it’s been slightly modified to remove the risk of small fingers getting in the gap of a partially inserted plug and touching the line pin, by adding insulating sleeves over that exposed part.  At the time that the BS1363 plug was introduced, two pin connectors ceased to be allowed, except for a few, very specific, applications.

Back to earthing systems.  In the early years, a locally-connected earth, to an earth rod buried in the ground adjacent to the house, was the only way of providing an earth connection.  It has some advantages, in that is ensures that the local earth potential in the house cabling is the same as the earth potential of the floor of the house, but it also has some disadvantages.  One disadvantage is that, being buried in the ground its effectiveness depended on how good a connection there was between the earth and the rod and between the house earth cabling and the rod.  Dry ground often meant a poor earth, with the house owners being unaware of the potential problem.  External cable connections were prone to corrode, or get physically damaged, again without the house owners being aware.  There were (and still are) ways to enhance the local conductivity of an earth rod, by placing more conductive compounds around it and making sure it is in good physical contact with the surrounding soil, but there are some soils that are notoriously difficult to make a reliable, long-term, connection to.  What’s more, the only way to be sure that such an earthing system was really working was to have an electrician come in and regularly test it, and few households bothered to do this.  A poor, or disconnected, earth, created significant and unseen safety hazard, and made the installation no safer than the old two pin plug system we started out with.

With the introduction of three pin plugs, and the need for a reliable earth connection, it became normal for the electricity supply companies (later the Electricity Boards, and currently the Distribution Network Operator (DNO) to provide an additional earth connection conductor to new houses.  This conductor was often in the form of the protective metal sheaths that were around the line and neutral conductors.   Having a reliable and well-protected earth connection supplied to the house removed much of the risk associated with the older earth rod system, and this soon became the standard way of providing an electricity supply.

There are some limitations to doing this, though, and they come back to something I mentioned earlier, the earth connection impedance.  If this is too high, because the supply earth cable is too long or too small, then the earth potential (voltage above the true local earth in this case)  at the house under a fault condition could rise to too high a level, and the level of electric shock protection could be reduced.  Nevertheless, this was not really an issue in towns and cities, where supply cables were relatively short, and had multiple earth connections along their length from the electricity boards equipment and connections.  Before long, with the boom in post-WWII housebuilding,  it became standard to use the earth supplied by the electricity board.

The only disadvantage of this system was really at the suppliers side, as they had to provide three conductors, insulated from each other, a line, neutral and earth.  Given that the neutral was ultimately connected to earth somewhere in the supply network, this was wasteful of cable, as the neutral and earth were always at almost the same potential with respect to each other.

Once the distribution network had a lot of earth connections in their local supply network, due to the need to earth every supply network transformer, it seemed obvious that there was now no real need to run a separate earth lead to a house, the neutral could easily be made to be at earth potential, so it could also be used as the main earth for the house.  In doing this, the neutral had to be renamed, so it was now know as the PEN, Protective Earth and Neutral, or occasionally the CNE, Combined Neutral and Earth.  At the house connection point, on the DNO side (as it is now, Electricity Board side as it used to be) the incoming neutral and the house earth were connected, with the earth made by a connection adjacent to the main neutral connection on the block that houses the incoming cable termination and company fuse.

Before harmonisation, this earthing system was termed PME, or Protective Multiple Earth on the consumer side of the installation, and term that is still in common use, even though, strictly speaking, it may not always apply to it’s post-harmonisation cousin, TN-C-S.

PME was, generally, no less reliable than the former system of supply a separate earth conductor, and was still significantly more reliable than the system where each house had it’s own earth rod.  It also saved the supply companies (by then nationalised Electricity Boards) money, as they only needed to provide a two conductor cable to many houses, rather than three.   There were still some installations where a separate earth conductor was needed,  usually because of the need to reduce the overall earth impedance at the consumer end to an acceptable level.

Also in many rural areas a separate earth connection or PEN connection was either never provided by the Electricity Board, or if it was, the impedance of it was too high to be safe, so the practice of having a local earth rod continued, and still does.  There are also specific applications where having a local earth rod has an advantage over a PME scheme, particularly where the PME provided earth has to be exported via a long cable on the consumer side of the installation.

Bringing things up to date

With harmonisation with the EU, all the standards were revised yet again,  with pressure being applied for the whole of the EU to use the same power supply, the same wiring standards, the same earthing systems and the same type of plugs and sockets.  It fair to say that the UK had to fight to retain its, very much safer, BS1363 plug, as many EU states still use non-fused plugs with no appliance cable current overload protection.  We had probably the safest domestic system in Europe, and weren’t going to give it up just because the EU said we should!  We did, however, have to standardise terminology, particularly relating to earthing methods, and standardise some wiring standards, as well as accept the EU 230V 50Hz system, rather than our older 240V 50Hz system.  In fact, we didn’t really ever accept the EU 230V system at all, all we did was change the allowable voltage tolerance, so that it’s now 230V +10%, -6%%, which, in reality, means we still run closer to our old 240V standard all the time, but can call it 230V to keep the EU happy………………..

Needless to say there were, and still are, other earthing systems around, some which were mainly used with commercial 3 phase power systems and some that were unique to other EU countries.  There is a good description of all the earthing methods allowable in the UK in BS7671, “The Requirements for Electrical Installations, IET Wiring Regulations” that’s been colloquially known as “the wiring regs” for decades.  That document, in principle, dates right back to that old two wire, no earth, system I described at the start, when it was decided that the government should create a standard for two pin plugs.

Nowadays these regs are produced by a joint committee, that is made up of three bodies, one of which I used to be a member of, as it happens.  The regs still retain the IET name, because the IET publish it and and remain the lead body, but it is produced by a joint committee, recognising that the importance of British Standards has been largely subsumed by EU standards, (and members of my former staff sat on the EU EMC Directive and LV Directive working groups too – not a lot of fun for them, I have to say).

You have to buy a copy of BS7671, and it’s not cheap, as there has been a drive to ensure that all this information is only made available to electricians, and they also have to pay to belong to one of bodies that allows them to certify domestic work that needs it if they are to do this type of work.  All told it’s a bit of a closed shop, intended to prevent ordinary members of the public from getting hold of technical information – not a policy I agree with at all.  Luckily there are sources online for most of the important information in the wiring regs, but some have to be viewed with suspicion, as the internet contains more false information that true information, unfortunately.

I have a copy of BS7671, Amendment 2, but sadly it’s now out of date, as Amendment 3 came out in 2015, after our electrical installation was completed.  I will happily let anyone who asks have an electronic version of my copy, but please just use it for background reading, as I haven’t yet had a chance to see the full extent of the changes that Amendment 3 has brought in (other than the need for non-flammable consumer units).

Getting back to earthing, there are currently five approved methods, all subtly, or not so subtly, different that are allowable, although only three are in common domestic use in the UK.  They are detailed on the IET website (http://www.theiet.org ) if you are a member or have access some other way, perhaps as a student, but most of the useful stuff needs to be paid for.  There is some good stuff on their forum and some free stuff for students too, which is useful, but no substitute for having the real standards and Guidance Notes.

In the harmonised earthing terminology there are five meaningful and descriptive letters:

T – from the French, Terre = Earth – you can tell where this lot’s come from, can’t you! (actually, some will argue it came from the Latin root, Terra, but blaming it on the French makes for a better story).





There is a very specific way of using this terminology, in order to avoid confusion, and believe me, it can be confusing for the uninitiated, because there are seemingly different meanings for Combined and Separate, depending on context.  For the purposes of most domestic installations, and in the context of self-build, there are really only three common systems that need to be considered, as it’s unlikely that you’d have anything other than these on a new build or new installation.  In all probability you would have the choice of just two of these three, making life even simpler.  There are other systems, but because they are fairly uncommon in the context of a domestic self build I’ve left them out of this bit of background reading.

The system that’s still in fairly common usa, is the oldest, the one where the earth connection is provided by a local earth rod or buried plate and there is either no earth provided by the DNO, or the earth provided is too high an impedance (greater than 0.35 ohms) to use safely.  Under the current terminology, this is referred to as TT, literally Earth – Earth, meaning the house wiring earth is connected to the local earth.  For me this is really the only term that is really meaningful; the abbreviation TT clearly indicates that the “Terre” is connected to the “Terre”, which seems logical when you’re looking at the house earth cable connected to an earth rod, or very rarely, a buried earth plate.  This diagram shows how a TT earthing scheme is connected, and also, most importantly, shows (by means of the dashed lines) who owns, and has responsibility for, each part:

In this diagram I’ve gone no further than show the three wires that connect to the consumer installation.  These wires must be 25mm² in cross sectional area for the Line and Neutral, and be no longer than 3m in length from the meter termination to the consumer equipment, be double insulated for the Line and Neutral, with a brown core for Line and a blue core for Neutral and would normally terminate in a nearby consumer unit (what would have been called the “fuse box” in times gone by).  The Earth wire should 16mm² in cross sectional area, must have a green/yellow sheath, and needs to be physically protected by conduit from the earth rod termination box to a protected location, like the meter box.  I’ll go into more detail about the consumer side of things later.

The next system is probably still the most common, largely because it was introduced during a period when large numbers of new houses were being built just after WWII,  and is the one where the electricity supplier (the DNO today) provides three separate conductors to the house, Line, Neutral and Earth.  The system is called TN-S, which, quite frankly, isn’t entirely logical, in my view.  The nomenclature is read from supply side on the left, to consumer side on the right, with the hyphen supposedly signifying a potential conductor separation point or terminal connection (except that it doesn’t, really, in this case!).  Here’s a diagram, similar to that above, that shows the separation of responsibilities as well as the conductor connections for a TN-S earthing scheme:

So, reading from left to right we have T for Earth, N for Neutral and then S for Separate.  There’s a sort of logic there, but not very clear in my opinion.  It translates as the incoming supply contains an Earth and a Neutral, and that they are separated.  This sort of makes sense, except that, in my view, the abbreviation would make more sense without the hyphen.  Just a personal thing, but I rather like abbreviations to be very easily understood.  Note that there is a change of responsibility with this system.  The Earth connection is now the responsibility of the DNO, so as well as offering a physically better protected Earth, this system also removes the responsibility for maintaining it from the consumer to the DNO.  The consumer only retains responsibility for the Earth conductors from the screw connection on the DNO head.

We  now get to the last system, the one where the Neutral and Earth are combined at the termination or within the incoming supply cable and are at the same potential, the one that had been referred to as PME for years.  This system is called TN-C-S .  Translated literally, this means Earth Neutral – Combined – Separate.

Nice and logical, isn’t it?  I mean, you can read that and immediately see what it means………………

Here’s a diagram of a typical TN-C-S earthing scheme:

As above, the dashed lines denote who owns and is responsible for, each part.  Note that, as with TN-S,  responsibility for providing the Earth changes from the consumer to the DNO with TN-C-S .

Looking at the installation it can be hard to spot an obvious difference between the the last two, as some DNOs use the same head for both TN-S and TN-C-S, just with an internal link removed for the former.  As before with TN-S, the first bit means that the Earth and the Neutral are both provided by the incoming supply cable,  but in this case the Combined term means that the supply is providing a Combined Earth and Neutral in the supply side, right at the interface between the DNO and the consumer.  This connection is properly known as the PEN, Protective Earth and Neutral.

The Separate term could be confusing, but in this case it means that the Earth and Neutral are not Combined at the consumer side, but kept separate, again following the “left is DNO, right is Consumer” sequence, and taking heed of those all-important hyphens in this case.  This is a bit more logical than  TN-S, in my view, as you can at least interpret where the actual connection point(s) between Earth and Neutral is/are, thanks to those pesky hyphens.

Most self builders can expect to get a TN-C-S supply provided by their DNO, unless there are some fairly unusual reasons as to why they can’t.  It’s now pretty common, even in rural areas, to provide a TN-C-S connection, as the DNOs have been gradually improving their networks over the years and there are now a lot more intermediate earth’s on the DNO network side than there used to be years ago and they tend to be a bit better maintained in my opinion(at least around here they seem to be, from what I’ve seen when driving around and about).

I’ll stop here for now, and continue with the consumer side, circuit protection methods, why we need them, how they work and what the differences are between different devices, in the next article, which will concentrate on external wiring, and use some of the external electric systems we have in our build as examples as to how I chose to balance risk, convenience, cost etc, whilst still remaining fully compliant with the regulations.



It seems this blog has caught the attention of the spam bots and now gets hit with around 20 to 50 comments a day, 90% of them from the same scammers trying to con people out of money for writing articles (and as some will know, I’ve written a few articles, had them published and know a bit about how the “writing for (very little) money” game works).

The worst scammer of all is an outfit called “writing job income” (and, no, I’m not going to be  daft enough to post their URL; it ends in .com and isn’t hard to guess, and I suggest no one looks it up and visits it, unless they really want to be scammed).

So, I’ve installed some stuff to try and reduce the amount of spam here, but it will only really work well against the spam bots.  Right now I’m reluctant to add the “prove you’re a human” stuff before people can comment, as I don’t like it and I suspect others don’t either.  However, if you get a pop-up when you’re trying to comment, then it means the system here suspects you’ve not read the post before writing a comment.

Hopefully this may reduce the amount of garbage I get in my inbox every morning, although I doubt it’ll stop those who are STILL being a bit childish and sending me junk out of personal spite – I do know who you are, you know, as some of you aren’t bright enough to cover up the trail you leave behind…………………..


Part Forty Six – Over-thinking things – Part Two

When going through the list of things that we hadn’t used consultants, specialists, etc for, I realised I’d forgotten about a few.  Well, it’s fair to say that I hadn’t really forgotten about them, but had forced common sense (an increasingly rare commodity) to dominate.

I’ll give just one example, but I’m sure others will have many more (especially when it comes to ecology, archaeology and wildlife!).   I had a rough idea of the ground we would be building on, as we HAD to have a hydrogeological survey for the borehole (no easy way out of that one, if you want a quote from driller).  The survey wasn’t expensive, and I could have obtained almost all I needed from the BGS website, plus a look at a lot of the local borehole drilling records, that shown the type of sub-strata and depth.

So, I knew that we were on the exposed top surface of blue gault clay, and that it was at least 3m, perhaps closer to 4m, above the water table.  I also knew that the gault was highly compressed here, so was almost a semi-hard mudstone.  The first thing I was asked by the foundation design structural engineer was the bearing strength of the sub-soil and whether or not the clay was subject to movement with varying water content (heave).

Now, many self-builders today will immediately pick up the phone, or more likely search the web, for a soil testing service, in order to get this information, for fear that if they don’t their house will fall down or subside.  Having lived in a Victorian built house, that just had stepped brick foundations around a foot deep, on to clay, and was still fine over 100 years later, I wonder quite why some have this reaction.

Back before we had all this highly technical (and expensive) kit for measuring soil bearing capacity, building inspectors used to do it, with a lump hammer and a bit of 2″ x 2″, marked with depth marks.  The subsoil would be exposed, the bit of 2″ x 2″, with a squared off end, would be placed on the subsoil and wacked hard with a lump hammer.  If it couldn’t easily be driven in more than about 4″, without really going at it, then the bearing capacity was reckoned to be “good enough”.  I did such a test.  The bit of 2″ x 2″ went in about an inch, and would go in no further, no matter how hard I whacked it.

In fact, this test is pretty good, 4″ penetration is generally “good enough” and is around 100kN/m², and it’s fairly unusual for any domestic foundation to need much more that this.  A slab foundation will usually need a lot less, as the load is spread over a greater area.  Also worth remembering that, as a rough rule of thumb, vertical bearing loads translate out at around 45 deg down and out from the point of load application, so a foundation that’s 1m² at the point of contact with the soil, is applying a load over about 9m² 1m down.

So, despite all the complexities of the big retaining wall, the borehole for water etc, we didn’t spend any money on specialist soil testing.  The wall structural engineer was “old school”, and knew damned well that the design was massively over-engineered, making any testing pointless.  The slab foundation even more so.  Our slab bearing area is around 85m², and the soil is over 100kN/m² bearing capacity.   Under the slab is a 200mm thick layer of compressed crushed stone, that increases the effective soil bearing area to just over 101m².  With a soil bearing capacity of over 100kN/m², the ground under this really simple foundation system could support a mass of well over 10,000 kg/m², or a total house mass of over 1000 tonnes.

In reality, a typical two storey house weighs around 3 tonnes/m², perhaps as much as 4 tonnes/m² for a very heavy stone built house, but more like 2 tonnes/m² for a timber structure like ours (including the foundation mass).  If we’re pessimistic, and say that our house has a foundation loading of around 3 tonnes/m², over the 85m² foundation, then the soil beneath “sees” a loading of around 2.5 tonnes/m² as a worse case (the reduction being due to the load spreading effect of the 200mm stone layer, increasing the effective bearing area).

Now, converting this back to units of force, it’s easy enough to work out what the actual soil loading is.  2.5 tonnes is a force of just under 25 kN/m², or under 25% of the soil bearing capacity.  This shows pretty clearly that anything that passes the old “2 x 2” test is more than good enough, with the sole exception of clays that are subject to heave with changes in moisture level (some are, like London Clay, some aren’t, like our hard Gault mudstone).  Even then there are easy (and relatively cheap) solutions to building on soils subject to heave – use screw piles.  Cheap and easy to install (a mini-digger with torque head can usually do the job).  The bearing capacity can be read out directly from the amount of toque needed to install them, so you know when you’re deep enough.  And, best of all, they can be installed very quickly and are instantly able to bear their full working load, unlike concrete, that takes time to cure.

The problem we have is that no one trusts tried and tested “old school” methods any more, and what’s worse, in this more litigious age, very few people are prepared to just use their judgement, they would rather you, the client, forked out a few thousand for another test or survey.

99% of this is obvious, but how much does it add to the cost of a new build?  For a one-off house, the total cost of all these surveys, tests etc, plus the cost of all the fees to the local authority, licence fees, building control fees etc, etc, can run into the tens of thousands of pounds, very easily, making the whole project non-viable if you’re looking to build a house for less than an equivalent house in the area would cost.

It’s no wonder houses are so damned expensive.  What with the price of land being high, and then there being dozens of people with their hand out for a slice of your cash, even before you’ve started any work, it’s likely that the land value and fees end up being the biggest part of the whole build cost, with actually building the house the cheap bit……………….

Part Forty Five – Architects and consultants, what are they likely to cost, and can you save money by doing some of this yourself?

First a bit of clarification.  Some have expressed a view elsewhere that this blog is in some way a revenue-generating device for me.  I can absolutely assure anyone reading it that it is the opposite.   It costs me money to pay for the web space, and I don’t gain any revenue from it at all.  I won’t  allow advertising here, and spend a fair bit of time deleting literally hundreds of spam comments, to keep it free of commercial influence, as far as is practicable.  As a consequence, whatever you read here is my personal view, and not coloured by any commercial influence.   My only intention here is to hopefully try and help others, who may learn from our experience.  If it saves them money, or eases their task, that that is all the reward I want.


I’ve been prompted by a discussion, following a couple of free podcast interviews I gave for House Planning Help:

here: http://www.houseplanninghelp.com/hph154-the-challenges-of-building-a-new-home-in-a-rural-community-with-jeremy-harris/

and here:  http://www.houseplanninghelp.com/hph155-do-you-really-need-an-architect-to-design-your-house-with-jeremy-harris/

to have a think about what “self-build” really means and how much money you are likely to pay out to others, even if you were to do all of the building work yourself.

All self-builders will approach their project with a different set of skills.  Some may have skills and experience in building trades, some may be architects or designers, but many will be people from non-building related backgrounds who just want, for a variety of reasons, to build their own home.

The UK is a bit unusual, in that almost all new houses are built without regard for the personal needs of the person buying them.  Very few people either self-build, or have a house built for them, here.  Other countries, like, for example, Holland, would find us a little odd.  There it is much more common for people to have a house built for them, rather than accept whatever a developer decides to build.

Another fact I found odd, was that only around 10% of UK houses are designed by an architect.  I don’t know about other self-builders, but the first thing I did after we’d found a plot of land was go around to try and find an architect, as I assumed all houses were designed by architects.  The fact that we struggled to find an architectural practice that were local, and competent in low energy house design, is, perhaps, not so surprising given how few houses architects actually design.

So, as a self-builder, who wants a low running cost house, should you instinctively try and find a specialist architect?  My view would have to be “it depends”.  If, like me, you are time rich (I’m retired) and cash poor, and if you think you can learn enough design and drawing skills (and there really aren’t a lot of drawings needed, for most house builds) then I think you can do as we did and not use an architect.  Doing this is a very big cost saving.  Architects typically charge between 10% and 15% of the finished build cost in fees, so we saved tens of thousands of pounds by not using one.

The flip side to that is that it meant that any design failings were going to be mine, but frankly, once you’ve signed off on an architects design you end up taking the hit on any failings anyway.  This implies that you have to be knowledgeable enough at the design sign off stage to know what is good and bad about low running cost house design, which means acquiring that knowledge anyway.

Then there is the engineering and thermal design.  Now this is something that is changing in the world of architecture, but quite slowly.  Architects have, traditionally, been taught as art and design graduates in the main, with the emphasis on the benefits good design can bring to living spaces.  No one would question the need for this, least of all me, as I found the “artistic” design elements the most challenging to get right, and I’m not really sure I did as good a job as a good architect may have done, even after spending perhaps 50 times longer on designing those elements.

Some architectural practices (and my personal experience suggests that it is the majority in the area around us)  pretty much ignore the thermal design and chuck their design across to an engineer, who not only has to work out how to build the house so that it’s strong and safe, but also has to work out all the details needed to minimise heat loss, control solar gain and ensure that systems can be put in place to keep the house at a comfortable temperature, all year around.

This is where there is now a conflict between pure architecture, and the need for low energy use.  Right at the start of the design process, thermal energy loss and gain must be foremost in the designers mind.  If that designer is an architect, then they must understand the thermal transmission issues surrounding glazing, corners, overhangs, things like geometric cold bridging, the thermal consequences of cantilevers where steel members have to penetrate the skin of the building, along with a whole host of other, material and engineering related issues.  I’ve met 13 architects now, who have visited our build.  One was very definitely on the ball and someone I would trust to design and build a low energy house, the rest varied from having a little knowledge, to the majority who had the view that “all this low energy stuff is the engineer’s problem, not mine”.

There are specialist consultants who can advise you on low energy design, and can work with an architect to ensure that the design can be easily engineered to use less energy.  However, most of these may try to persuade clients to adopt the certification standard of the body that approved them, and there is a substantial cost to doing that.  The most common, and best recognised, low energy standard is Passivhaus, a certification standard developed around 20 years or more ago in Germany, by the Passvhaus Institut.  It is a very good standard, perhaps the gold standard for low energy homes, but certification comes at a significant price.

A Passivhaus consultant may have quite reasonable fees (typically around 1 to 1.5% of the build cost) but there are a lot of additional, almost hidden costs from going down this route.  The biggest, in cost terms, is that you either have to use Passivhaus Institut approved products in building the house, or provide evidence that their performance is such that they could be approved by the PHI.  This can add a lot to the cost, as not unreasonably, manufacturers charge a premium for any product they have paid to put through the PHI approval process.  The end result, for the self-builder, is that PHI certification can easily add 5% to the build cost in total.

Using our build as an example, here is a list, roughly in time order, of activities where we either did employ someone, or could have done, and then after it, the approximate cost savings for each item:

  1. Finding the plot. There are plot finding agencies, and we signed up to a couple, but generally we were very, very disappointed with what they had to offer, and the costs were high.  We found our plot via a local estate agent, so incurred no commission to any plot finding agency.
  1. Designing the house for planning: As mentioned, I couldn’t, at the time, find an architectural practice locally who I would trust to design our house, so I spent around 6 months or more learning how to do it myself.  That has now changed, and if anyone wants a recommendation for a good, local, low energy aware, architect, contact me, as I now know of one.
  1. Submitting the planning application: Having designed the house, I found submitting the planning application the next most challenging thing to do.  Our plot had a very chequered planning history, and so my DIY planning submission needed a lot of work (listen to the first of the podcasts linked to earlier for more detail).
  1. Flood risk assessment: Our planners took advice from the Environment Agency and wouldn’t accept a planning application without a formal Flood Risk Assessment.  I asked around, and the cost for this was going to be between £1500 and £4000.  I wondered what was involved, so looked at a few that had been submitted with other planning applications and realised that I could get the data for free (it’s a combination of data from the EA and the BGS) and write my own Flood Risk Assessment.  I did this in around one evening, and frankly it wasn’t a lot of work.
  1. Detailed house thermal design. Here I saved a great deal of time and work by choosing a timber frame and foundation system supplier that guaranteed Passivhaus levels of insulation and airtightness.  They had their own structural engineer to sign the design off, which eased the Part A building regs compliance issues.  I was able to look at the detail design and be assured that it was cold-bridge free and that the insulation level, and more importantly, the high decrement delay factor for the chosen wall and roof insulation, would perform as I wanted.  I modelled the thermal design, initially using a fairly simple, heat loss only model (if anyone wants a copy, ask, it should run on any spreadsheet programme OK).  I then put all the details into FSAP, a SAP modelling spreadsheet required for Building Regs, and finally, when I was confident that the design was close to finalised, I spent around 2 days putting all the details into the PHI thermal and energy modelling spreadsheet, PHPP.  The latter is expensive, and given the small difference in output between the simple model I will let anyone have for free, combined with the solar gain and energy use parts of SAP (again available for free – contact me) I’m not convinced we needed PHPP.  Our aim was to design and build a “no energy bills” house, not get any form of certification.  We also wanted to save money wherever we could, and I was happy to learn new skills if doing so saved us money
  1. Ground works. Our plot needed a lot of ground works and this divided itself into two parts, rather naturally, the levelling of the site and the construction of a big retaining wall.  The first was just digging away 900 tonnes of soil, the second a substantial retaining wall.   The design of a large (~3m high x 35m long) structural retaining wall seemed to need a structural engineer.  The first structural engineering company I went to wanted an initial payment of £4000, plus site visit fees of £250 per visit, plus unstated additional fees.  I was a bit shocked, so sat down, read Eurocode 7, BS8002 and BS5628, then wrote a spreadsheet to do all the retaining wall design calculations.  Luckily I had a soil condition report that came with the plot paperwork, so already knew the local soil and sub-soil properties.  Having found it wasn’t hard to design a retaining wall, I ran into the problem that building regs and your insurance company will only accept one designed by a structural engineer who has indemnity insurance.  I found a local one, we chatted, and I got an approved wall design for a very modest fee indeed.  The rest of the ground works was straightforward, and needed no consultants or experts
  1. Submitting the Building Regulations application. Some people get their architect or project manager to do this, for a fee, typically a few hundred pounds.  I looked at the drawings I’d already done, together with the drawings of the structure that MBC, our timber frame company had provided me with for approval of the design, and decided there was very little extra needed to compile a full Building Regs submission.  It took me around a day of work to do one specific section drawing and tidy up some other drawings, plus add some text explaining how we were complying with the regs.  Not really hard to do, and there are details of this, together with the planning application, in Part Fifteen of this blog, here: http://www.mayfly.eu/uncategorized/part-fifteen-the-site-is-finally-ready/ ).
  1. Managing the build. I started off thinking that I’d use a project manager (architects can also project manage builds, for around the same fee), and interviewed a few.  They all said much the same, which was they would charge around 10% of the build cost to manage the build but would probably save that by getting better prices from sub-contractors.  As we were only going to subcontract the electrical work and some detail work, like the larch cladding, and I was going to do the bulk of the other work  there wasn’t really much scope for a project manager to save us money on sub-contractor cost.  The main issue was whether or not I felt comfortable managing the sub-contractors we did use and taking responsibility for completing the house.  The  ground works company had managed the site for all that work, and all I’d done was a bit of over sight.  MBC, the timber frame company were going to install the insulated slab foundation and erect, insulate, membrane cover and batten the house, so all that was left to manage were all the internal details, and I felt quite happy doing that.
  1. SAP assessment fees for building control sign off. I did all the SAP calcs, but found you have to have an assessor to lodge the paperwork – no matter how competent you are at using SAP, you cannot DIY the data base entry!  I negotiated with an approved assessor, emailed my as-built FSAP calculations as a complete file, ready to be lodged on the data base and he charged me a modest fee to just put his name and number on it and lodge it for me.  This still annoys me!


So, what did we save, just on external consultant/architect/project manager costs, by going down the DIY route, and how much time did it cost me to be able to make this saving?

In the order of the list above, here are the rough savings for each item:

  1. Between £500 and £2000, depending on the agency fee structure, say £1200.
  2. Around 10% of the build cost, so around £25,000
  3. Around £1000 to £2000 for a specialist planning consultant, say £1500
  4. Between £1500 and £4000, say £2800
  5. Around 1 to 1.5% of the build cost, so around £2500 to 3250, plus the “Passivhaus Premium” for approved matierials, which would have added another £5000 or more. In total I think we saved well over £7,000 by not going for PHI certification
  6. Structural engineer fees – using a local chap who knew the area and having done a lot of the base work myself, saved around £4,000 on fees
  7. Submitting the Building Regulations application and drawings. Typical cost around here would be about £500 to do this
  8. Managing the build. A project manager would have charged around 10%, and architect, as a part of a design and build contract perhaps less, maybe 5%.  Not wanting to double account for savings, lets assume a saving here of £12,500
  9. SAP assessment fees could have been a “double whammy”, as we could have incurred fees for the Building Regs design SAP submission (which I did myself) and the final, as-built, SAP Assessment that must be lodged on the government data base.  In total we saved around £200 by going down the DIY route.

Adding these savings up gives a total saving of around £54,700

This saving came at a cost in my time, though.  It took me a lot more time to do all of these elements than it would have taken a professional, who already had the knowledge and experience.  For example, I spent at least two weeks just learning all the building regulations, and understanding which applied.  I spent even longer on learning about low energy house design and creating spreadsheets to make the calculations simpler.   I spent longer again on studying domestic architecture and learning about the vernacular architecture and design for the AONB that our new house is within, and how that might be adapted to be both low energy and compliant with local planning design guidance.  I also had an advantage, in that I’m a retired scientist, so both the physics and mathematics were, for me, pretty easy, and even learning the structural engineering needed to design a gravity retaining wall was only around and evenings work.

All told I think I spent around 1500 hours of my time on all the above work, plus around £50 in the cost of paper, printer ink and postage.  I consider that reasonable recompense for my time, as I’m retired and on a pension, as it works out as a tax-free “income” of around £36 per hour, not a sum to be sniffed at, and a bit more than my pension pays me!

Could anyone make a self-build saving like this, on stuff where you don’t actually get your hands dirty?  I’m not sure.  If you have the time, a willingness to learn new skills, and a basic education up to around O level mathematics and physics, then I think it’s entirely possible.

Finally, did we succeed in our ambition, to build a “no energy bills” home?  Well, the heating and hot water systems, along with everything else, have been on continuously, with the thermostats set for 20.5 deg room temperature, for over a year now.  In the past week or so I received both the electricity bill (the house is all electric, there is no other form of external energy input) and the feed-in-tariff payment for the solar panels on the roof.

This was for a high energy use period (we’ve had overnight temperatures of well below freezing on several occasions) and a low electricity generation period (November is always a bad month for generation, as is December).  Both the electricity bill and the FIT statement were for the same period, September 2016 to December 1016.  The electricity bill was £113.10 and the FIT payment was £139.98, so we’ve over-done it a bit, and built a power station!  Over the year, the house generates at least twice as much zero-CO2 energy as it uses; in a good, sunny, year probably closer to three times as much.

To conclude, I think we’ve surpassed our goal, by a significant margin.  We have built a house that has cost around £1340/m² in build costs, which is around the median cost for most self-builds, we’ve exceeded our goal of building a “no energy bills” house and as a bonus we get a small, tax-free, income as being a “micro power station”, plus we have no water or sewage charges, as we’re off mains water and drainage.  Sadly, we do still have to pay Council Tax, though………………….

For those interested in the daft numbers on the EPC (Energy Performance Certificate) and EIR (Environmental Impact Rating) bits of paper, then we have a final EPC of A107 (where A100 is notionally a zero energy house) and an EIR of A107, too.

The latter is interesting, as it states that the average UK house causes 6 tonnes of CO2 to be emitted to the atmosphere every year, and our house causes -0.4 tonnes of CO2 to be “absorbed”, in effect.  For those into this eco stuff, our house has the same environmental impact on the atmosphere as around 40 to 50 mature trees  -except we couldn’t fit that number of mature trees on the plot, so arguably it’s more beneficial for the atmosphere to build houses like this on land than to plant trees!

Part Forty Four – Over-thinking things – Part One

From the very start of this project I have now realised that I have wasted hundreds of hours thinking far too much about things that really don’t need worrying about.  In this episode, I’m going to try and focus on a few of them, I’ve no doubt more will come up in later posts.

I mentioned in a reply to Mike in the previous part that I had wasted a lot of time doing things that I thought would be needed for the building control completion inspection, but that it turns out weren’t.  The same is true about so much of this build, that I think it’s well worth trying to summarise some of them in a single post.

Firstly, I should point out that as a retired scientist I find it far, far too easy to get sucked in to investigating details and finding out why things behave as they do.  Sometimes this is a good thing, but 90% of the time it leads to a great deal of wasted effort.  The classic is the initial house design.  I was obsessed with how to heat it and making sure it had enough passive solar gain in winter.  It didn’t even cross my mind that it might  need cooling, neither did it cross my mind during the design stage that having a house deep into a cut out into a south-facing hillside, near the bottom of a fairly sheltered valley, would mean that the micro-climate around the house was significantly warmer than the average for our area, which is on the edge of Salisbury Plain – a notoriously cool place!

One consequence of this is that the local climate data from the Met Office isn’t very representative of the temperatures we get in this valley, and even less representative of the local temperature around our house, set, as it is, 2.5m down into the hillside and sheltered on the North and part of the East by the ground a couple of metres away.  This meant that the climate data I used both in my own spreadsheet and in PHPP was in error.  My estimate is that in summer our average local temperature is around 2 to 3 deg C warmer than the Met Office data set for the area, and in winter at least 1 deg C warmer, maybe a bit more.

The effect of this is to skew the heating requirements downwards, and create an overheating risk that didn’t show in my spreadsheet, PHPP or SAP.

Curiously, most of the overheating comes from the East, not the South.  The sun rises well North of East in summer, so the East elevation has a long period of direct exposure.  This shows clearly on the cladding; the larch on the East side has faded a great deal more than that on the South or West faces.  The bedroom with a window facing East overheated badly, so this has been mitigated by applying heat reflecting film to the outside of that window and by replacing the very thermally lossy thermal store with the Sunamp PV (the services area is adjacent to the East bedroom).

The kitchen East-facing window also gets a lot of solar gain, as does the South facing one.  The dark grey of the stone window internal window cills, and the kitchen worktops, exacerbate this, by heating up and convecting and conducting heat into the room.  By contrast, the solar gain from the South facing gable is not that massive.  The large roof overhang limits it, but adding solar reflective film has also made a big difference, such that cooling is not often needed now.

I wasted more time thinking about complex heating and cooling control systems than you would believe.  I built several versions of rather sophisticated controllers, using internal and external sensors measuring air temperature (inside and outside), floor slab temperature, relative humidity, flow and return temperatures from the floor heating, you name it.  I had weather compensation, predictive heat demand from rate of change of outside temperature and very accurate control of the floor slab temperature, which, in a low energy house, is directly related to the heat output at any time and the house internal temperature.

All this was a complete and total waste of time and money.  At a guess I spent around 500 hours playing around with different systems, plus a few hundred pounds building ever-more sophisticated controllers.  I can’t believe, now, that controlling the temperature of a passive house is really very, very simple.  There is no need for any complex controls or expensive valves, sensors, etc.  The house will pretty much look after itself when it comes to heating in winter, with just a very simple room thermostat controlling the whole ground floor under floor heating.  It’s a complete and total waste of effort, time and money to invest in anything clever or sophisticated to regulate the heating, when a simple and cheap room thermostat works so exceptionally well.

We’re in the heating season now, and have had temperatures down as low as -6 deg C on a couple of nights.  The only heating has been from the under floor system, as we don’t ever use the Genvex active MVHR for heating at all – it just isn’t needed and, anyway, it tends to dry the air out a bit too much.  The coldest temperature I’ve seen in the house has been about 20 deg C first thing in the morning, the warmest (this December) about 21 deg C.  The floor slab sensor now only displays the temperature, it doesn’t control anything, and that shows a steady temperature of around 21.2 to 21.8 deg C.  The heating system comes on about once every two to four days, for around an hour, and usually pumps water at about 23 to 24 deg C around the floor slab.  Any hotter than this and the house will heat up too quickly, and there will be a noticeable overshoot in the floor, and room, temperature.  On very cold nights, the heating will come on in the morning. A couple of weeks ago we had three nights in succession where the heating came on for an hour or so every morning.  The room thermostat is on the wall, in the shade, on the ground floor, pretty much in the very centre of the house.  It’s currently set to 20.5 deg C, and has a 0.1 deg C switching hysteresis.  This means it turns on at 20.5 deg C, and off at 20.6 deg C.

Because there is a lag between the floor slab warming up and the room air warming up, the room temperature will continue to slowly increase through the day as the slab gives up heat, even though the heating is off.  This seems ideal, as it means that the temperature tends to peak in the evenings, at around 21 deg C if there’s been no one in the house and no solar gain, then drop very slowly overnight on a very cold day.  The rate of change of temperature is so slow that the subjective effect is that the house is at a very constant temperature all day.  This isn’t surprising, as the daily room temperature variation rarely exceeds 1 deg C in winter and is often only around ¼ of that, unless the weather is very cold.  Our old house, even with double glazing, good loft insulation and cavity wall insulation starts to cool around half an hour after the heating goes off, and loses around 1 deg C every couple of hours if the heating is left off during the day in winter.  We often see a 4 to 5 deg room temperature variation in winter in the old house, and it’s very noticeable that the new house just feels far more comfortable even if the heating hasn’t been on for two or three mornings.

So, the moral of this tale is to forget about complex heating controls in the low heat loss house.  Forget about zoning, as all the rooms will end up being close to the same temperature, forget about programmers and clever thermostats, as all that is needed is a low temperature heat source into the floor plus a simple high resolution room thermostat situated near the centre of the house.

Had I know this at the start I’d have been amazed.  In fact, quite frankly I’d never have believed it.  I’ve wasted hundreds of hours trying to solve a problem that turned out to be imaginary!

I’ve just realised that this is all getting a bit too long, and that there are other things I’ve wasted time over-thinking that I’ll need to put in other posts.  To finish, these are the diagrams of the floor  heating and cooling system.  This excludes the Genvex active MVHR, which is separate and only ever used occasionally for summer cooling now; it’s never used for heating in practice, and has it’s thermostat set permanently to 19.5 deg C, and if the floor heating is working then the house never ever gets this cool, so it’s really just a backstop in the event of failure of the main system:

The above diagram shows the ground floor part of the system.  The thermostatic valve on the UFH manifold is normally set to around 24 deg C, which is right near the very bottom of its control range.  If the weather turns extremely cold (below about -5 deg C or so) then there is a very slight benefit in turning this temperature up by a degree or two, but also a risk that by doing so there will be a temperature overshoot.  The system is very sensitive to small changes in flow temperature, and if there was one thing I might, possibly, change it would be to add a very limited weather compensation capability to the flow thermostat.  I’m not sufficiently convinced yet that it’s worth the effort, for the handful of days in a year when it might, possibly, give a small benefit.  It’s worth noting that a lot of thermostatic mixer vales won’t control down to 23 to 24 deg C or so.  Ours is a Wunda manifold, and the mixer valve uses a sensor set into a pocket in the flow manifold, and as far as I know is one of the few that will control well down at such low flow temperatures.

For those that have doubts about the effectiveness of such a simple control system, here is some temperature data from the house logger.  The logger collects data every 6 minutes and measures and records lots of different parameters, including room Co2 and room RH, but this plot just shows the room temperature (red) at around 1.2m above floor level in the living room and outside air temperature (blue) measured at the sheltered North face of the house.  For the first few days of this plot I had the room thermostat set to 21 deg C, which turned out to be a bit warm, so I turned it down to 20.5 deg C, a change that can be seen around 11th November:

From the above, it’s clear that the outside temperature varies very wildly, whilst the room temperature is relatively stable, not changing by more than about 1 deg C.  Most home thermostats can’t regulate to 1 deg C, the best they normally manage is around 2 deg C or so, and, as mentioned before, our old house changes temperature inside by several degrees per day, with the thermostat set to 21 deg C and the gas boiler running for a fair part of each day to try and keep the house around 21 deg C.

The most important single aspect of this whole under floor system, and the one that has the most dramatic impact on the evenness of the house temperature, is the fact that the circulating pump is running all day long, every day (but turned off at night) whether heating is needed or not.  This circulates water around the whole floor slab and evens out the temperature, taking heat from the warmer areas and using it to heat to cooler areas.  I can’t underestimate how important this is – it really does make a massive difference to the comfort level, all at the cost of less than 20 watts to run the low energy Grundfos pump on the under floor manifold all day.


The diagram above is mainly concerned with the DHW system, which uses pre-heated water from the ground floor buffer tank.  I’ve included it here for completeness, and as it shows the expansion vessels and filling loops for the under floor piping and ASHP (filled with antifreeze mixture) and the buffer tank filling loop (filled with normal inhibitor).  The buffer tank is run at a very low pressure, 0.3 bar cold and 0.5 bar warm, with a 1.5 bar pressure release valve.  This is because the buffer tank isn’t a pressure vessel, and is designed for a working pressure of not more than about 1 bar.  This arrangement was used to avoid having a header tank and overflow – it means the system can be sealed, a significant advantage.

Part Forty Three – Completion! (and getting the VAT back……………..)

After much faffing around with details and paperwork, we finally have a Completion Certificate!

Getting things ready for the final Building Control inspection turned out to be an exercise in doing loads of work that wasn’t actually needed.  Very frustrating, but a consequence of me not having been through the process before, and assuming that Building Control would want more evidence of compliance with the regs than they actually did.

I had prepared copies of things like the water usage calculations with evidence of measured flow rates from all outlets, and none of that was needed, for example.  I’d also prepared reasons justifying the three pressurised systems we have, and why they did not need sign off against Part G by a competent person, and again none of that was needed.

In the end, when I’d got everything ready, with piles of paperwork stacked up ready to be checked, it turned out that the Senior Building Control inspector who came out was so enthusiastic about the build that he walked around for five minutes and declared he’d issue a Completion Certificate that afternoon.  All he needed was my confirmation that the SAP EPC and the Part P certificates had been lodged on the appropriate databases, and that was it.  The only thing actually checked was that the rear door entrance ramp, external wheelchair turning space, rear door threshold and width and downstairs WC access were Part M compliant, but this was just a visual check – nothing was measured.

I did give him a good walk around the whole house, pointing out all the things that had been done in accordance with the regs, but to be frank, I think he just sort of assumed from my general approach that I had complied with everything, and nothing was checked in detail at all.  This placed quite a lot of trust in me, as the previous inspection had been when the insulation was being pumped in, before the cladding went on or the roof, and before the wiring, plumbing, heating, plastering etc had been done.

Having got our Completion Certificate I set about putting the VAT reclaim together.  I’d been sorting out invoices and annotating them and adjusting the VAT where there were ineligible items listed, plus I’d kept copies of the exchange rates that applied at the time for everything purchased from the EU with VAT paid in another country.  To make things easier to handle, I stapled each till receipt to a sheet of A4 paper, and bound these in groups (using a hole punch and banker’s tags) so that each group of receipts matched a single page of the reclaim spread sheet form.  I recreated the receipt form parts of the VAT reclaim form as spreadsheet pages, which made getting the arithmetic right a lot easier (I can try and attach, or email, a blank of this spreadsheet form, if anyone wants it).  I also added a serial number hand written on each receipt, in order, and used an extra column on the form to list this number, which made double checking that the forms matched the physical receipts a great deal easier.

I took the view that the easier I made it for HMRC to check the less hassle we would get, so doing some things that weren’t strictly required, like arranging the receipts in date order and adding unique serial numbers, might make our lives easier.  Don’t underestimate the time it takes to do this!  All told I spent around 20 to 30 hours just compiling receipts, filling in the forms and cross-checking.  I then sent the whole lot off by secure, insured, delivery to HMRC and waited.

The first request back from HMRC, around 2 weeks later, was for a full set of plans and planning permission, together with a request for me to fill in a signed statement as to how much VAT should be removed from the claim for the value of the bike shed shown on the planning approval plans.

To say this was contradictory is an understatement.  I’d sent all the plans and all the planning permission documents with the receipts (as required), and they must have looked at them, as the planning permission plans included provision for a bike shed (required under the old Code for Sustainable Homes that applied at the time we submitted the plans).  Bike sheds, even when attached to a garage, as our proposed one was going to be, are NOT eligible for a VAT reclaim, even if they are a planning condition, or required by some regulation.  The fact that HMRC had picked up on the bike shed on the plans meant that they must have read the planning permission and plans I sent, so why ask me to send them again?

You can’t deal with them by email or phone, so the only thing to do was to send them a letter explaining that we didn’t build the bike shed, as the Code for Sustainable Homes requirement was withdrawn in between us submitting our plans and them being approved, so we’d verbally agreed with the planning officer not to build it.  I also included photos to prove we hadn’t built it (it was shown on the plans as a lean-to against the side of the detached garage) together with emails and the final conditions sign-off from the planning officer.  I also sent HMRC another copy of the planning permission and plans they’d already got – I assume they misplaced the ones they’d originally received and reviewed, hence them needing to ask me for another set.

Another couple of weeks went by and we received a letter telling us that well over £1800 pounds of our claim had been rejected, as it included an ineligible item and that the balance of £8,300 would be paid to us within 10 days by BACS transfer.  The implication was that this was the end of things, but they did give details of their appeal procedure.

I wasn’t too happy at losing well over £1800, so checked and found one error on our kitchen receipt that I’d not spotted.  We bought the kitchen units as supply-only, except the kitchen company also supplied the stone worktops, and they were supplied on a supply and install basis, as they had to template the kitchen after I’d built it, cut the stone to fit, then install it.  There was around £500 of VAT for this that shouldn’t have been charged.  The kitchen supplier should have put this on a separate invoice as a supply and install item.  I didn’t spot it amongst the dozens of lines on the kitchen receipt, and HMRC disallowed the whole kitchen unit VAT on the basis of this single error on the part of the supplier.

It was an error, too, as I’d given the kitchen supplier evidence that the supply and install part should be zero rated, and that VAT should only be included on the supply-only stuff.   I went back to the kitchen supplier, they pulled the file and found my copy of the house plans, the request from me to zero rate the supply and install part, together with their copy of the receipt.  They were happy to write a note saying that they had made an error on one item (out of around 40) on the kitchen receipt and confirm that all the kitchen components had been supply-only, except for the supply and fitting of the stone worktops.

I appealed to HMRC immediately, sending them an explanatory letter, with written evidence from the kitchen supplier, and they have said they will decide the appeal by 11 January 2017.  The kitchen supplier are also looking at how to refund us the ~£500 VAT they charged us in error.  They’ve admitted it was their error, but their accountant is working out how to deal with it.

My mistake, in part, as I didn’t spot that one line in the 40-odd items that made up the kitchen components.  It’s now in the hands of HMRC and the kitchen supplier as to whether we get all, or some, of that VAT back.

The moral of this tale is to check, check and check again, before you send your claim in to HMRC.  You cannot telephone them or email them to explain things or question anything, as they warn you that attempting to do so will increase the time it takes them to process your claim (my guess is that you go back to the end of the queue if you try and contact them, midway through the process).

We’re now in the process of getting our old house ready to market, hopefully not long after Christmas, and begin moving in to the new house, as the new furniture arrives (probably late January, early February).

All the house systems have been up and running for the best part of a year now, with a few teething problems, but nevertheless everything generally all works OK.  The temperature control is extremely effective.  Temperature stability is excellent, no matter what the outside temperature does, with the combination of relatively low mass, relatively high heat capacity, good surface conductivity, high insulation level, good airtightness and heat recovery ventilation and a tiny bit of heat put into the floor every day or two when it’s very cold, working well.

The key is that the house has a high thermal time constant, due primarily to the good insulation, high decrement delay factor and high heat capacity.  It proves beyond any doubt whatsoever that mass has sod all to do with maintaining a steady temperature, in fact I think there’s a strong case for advocating that too much mass and too little thermal capacity, could well end up with a less comfortable house.  This is, without a doubt, the most comfortable house we’ve lived in ever.

There have been a some changes to some of the systems, in the light of experience, so the next blog entry will focus very much on the house as-built, and this may well mean that some earlier blog entries may no longer represent what actually works.  Things evolved as we went along, primarily to do with the hot water system, the heating controls and the water treatment system.  For example, I found that controlling the slab temperature was a poor way to keep the house at a constant temperature, even though theory suggested it should be better, so the floor temperature sensing and control was removed and replaced by a much simpler room thermostat, that controls the house temperature far, far better than even the best proportional, weather compensating, floor temperature control I could device ever managed.

More on all this in the next episode.

Part Forty Two – Water Treatment

This blog entry is just looking in detail at the ozone treatment part of our borehole water system.

Our borehole water has a high concentration of ferrous iron, this is what’s often called “clear iron” as it doesn’t colour the water.  It’s fairly common in water drawn from deeper aquifers, particularly in areas where there are natural iron deposits or soft (often slightly acidic) water that dissolves iron (and other metals, like manganese) from the surrounding rock.  In our case our water comes from the Lower Greensand formation, an aquifer that is known to have water with high concentrations of ferrous iron as well as dissolved hydrogen sulphide gas (the “rotten eggs” smelly stuff).

The traditional way to remove ferrous iron, manganese and hydrogen sulphide from water is to just add oxygen to it, usually in the form of air, but it can be by using an oxidising catalyst.  The most common oxidising catalyst is manganese dioxide, used in a filtration bed.  This works OK, but it does eventually need replacing, or regenerating in some way, as it will lose its ability to oxidise after a time.

For those interested in the chemistry, ferrous iron converts to ferric iron (rust) when it’s exposed to oxygen.  Whereas ferrous iron is fairly soluble in water, ferric iron isn’t really at all, so when this forms it deposits orange/brown particles in the water that can be filtered out.

Hydrogen sulphide can also be reduced by oxidation, leaving insoluble sulphur particles in the water that can be filtered out, but because the hydrogen remains dissolved after oxidation it is better vented off to the atmosphere if possible.

A significant issue here in the UK is that not many people have borehole water supplies, and even fewer have borehole supplies where the water has ferrous iron, manganese or hydrogen sulphide present.  Historically I think this is probably because these contaminants mainly come from deep boreholes and areas where they are found may have historically used surface water springs or wells before the advent of widespread mains water supplies, so using water like this was avoided if possible.

In the US, where most rural properties use boreholes and wells for water, and “city water” is only available in fairly big towns and cities, necessity has led to a plethora of treatment systems to make all sorts of water potable.  I found that there is a great deal of knowledge readily available from US drillers and water treatment equipment suppliers, just because using a private supply is normal there for most of the population.  I’m indebted to a couple of Americans who took the time to give me a great deal of advice by email.  Without their help I’d have far less understanding of the best way to treat our water.

The problem with all this expertise being in the US, means that the vast majority of the equipment to deal with water treatment is made in the US, too, and it is pretty expensive to import to the UK.  There are some UK suppliers of good US-made treatment equipment, but generally they only stock commonly-used stuff.  The best supplier by far, and one that I would strongly recommend, both for their customer service and for their technical knowledge, is GAPS Water Treatment in Rochdale, Lancashire.  Not only do they supply complete systems for most commonly encountered water treatment needs, but they also stock lots of spare parts.  This latter capability saved me a great deal of money when I wanted a bit of kit they didn’t stock, but found I could easily make it using a cheap (around £5) spare part from them.

So how does our system work?  The borehole pump is a standard item, a submersible high pressure pump that feeds water from half way down the borehole, via a length of 25mm MDPE pipe, to the water treatment shed at the rear of the house.  One problem with our borehole is that if I pump water at a rate over about 15 litres per minute very fine sand gets pulled through the filter media around the borehole liner.  If I keep the flow rate below this I get no sand at all, so I had to limit the flow rate filling the two 300 litre, and one 100 litre, pressure storage tanks to less than 15 litres/min.  This sand problem is common in some regions of the USA, so an American company has come up with an automatic flow rate limiter (a bit like an industrial version of the things used to limit shower flow rates) called a Dole Valve.  This maintains a constant flow rate no matter what the pressure, within limits.  I chose one rated at 2.5 US gallons per minute, which is about 9.5 litres/min.

One advantage of fitting the Dole Valve in series with the main water feed, apart from the control of flow rate, it that it generates a pressure drop across it, that can be quite high.  Typically our pump line will be at around 10 bar when water is flowing, whereas the pressure tanks run at between 3 bar minimum and 4 bar maximum, so there is always between 6 bar and 7 bar pressure drop across the Dole Valve.

This pressure drop is very useful, as it allows the use of a simple, low flow rate, venturi to be used to suck air, or in our case air and ozone, into the water supply, whenever the borehole pump is running.  This is a very common way to aerate water in US private water supply systems, and there are several manufacturers of small venturis, combined venturis with adjustable flow regulator bypass valves or even one venturi with an automatic bypass valve that uses the internal control washer from a Dole Valve, in effect, in the bypass line.

Venturis are interesting, and worth explaining in a bit more detail.  Back around 1738 Bernoulli found that if you increased the velocity of a flowing liquid, by reducing the size of hole it was flowing through, then it created a pressure drop (see here for more details: https://en.wikipedia.org/wiki/Bernoulli%27s_principle).

I’m using a tiny venturi (it flows less than 0.5 litres/min) in parallel with the Dole Valve, to both create suction from that pressure drop, which sucks in ozone and air, and to mix the ozone and air with the water, like the fine spray from an aerosol.  This ensures that as much as possible of the ozone, in particular, gets dissolved in the water, where it very quickly oxidises anything in it (and kills off bacteria, viruses and cysts, as a side effect).  Ozone is a very good sterilising agent, because of its very powerful oxidising properties, but that’s not principally why I’m using it.

Perhaps an explanation of what ozone is might be useful here.  Ozone is a form of oxygen, known as an allotrope.  Oxygen is fairly reactive (it’s what causes almost all the corrosion we see on anything) but it’s also stable, as long as there are two oxygen atoms joined together.  Almost all the oxygen in the air is made up of two oxygen atoms joined together tightly, and is referred to as O2.  If you chuck a load of energy into oxygen, then you can force it to split apart and reform with three oxygen atoms joined together, O3, ozone.  The snag is that ozone is highly unstable and exceptionally reactive.  It desperately wants to return to the stable allotrope, with just two atoms, so constantly want to try and find a way to get rid of the extra oxygen atom, as quickly as it can.

This is what makes ozone very useful for converting water-soluble ferrous iron oxide (FeO) into insoluble ferric iron oxide (FeO3), as ferrous oxide is also fairly unstable and will grab any oxygen it can find to turn into stable ferric oxide.  Much the same happens with other soluble metal oxides in the water, like manganese, or anything that is readily oxidised, like bacteria, viruses, cysts etc.  The other useful attribute of ozone is that it is so highly reactive that a small amount will oxidise relatively large amounts of water.  Ozone is more reactive that chlorine or hydrogen peroxide, and will oxidise just about anything, including sulphides, some plastics and most metals.  There is more on the characteristics of ozone here: https://en.wikipedia.org/wiki/Ozone

So, I now had a way of being able to suck air, or ozone, into the supply water, by using a small venturi, but I needed three other bits of kit to make this a practical way to treat water;  an ozone generator, a reaction tank where the oxidation could take place and a filtration system to remove the oxides and dead bacteria, etc from the treated water.

The ozone generator

Ozone is easy to make using electricity, every time there is a spark generated ozone is generated (it’s the smell people associate with sparks, or even nearby lightning).  Sparks are also dangerous, though, and they erode whatever is sparking (like in an arc welder, for example).  Luckily there is a way of making ozone that doesn’t need sparks and that’s by using what’s called a corona discharge.  This occurs where you have a high voltage on two metal parts, separated by a insulator.  Around the edges of any sharp edge, a corona discharge will occur, which is fairly quiet (just a gentle hissing noise) and most importantly it doesn’t erode the metal electrodes.

Because ozone is so useful for oxidising things and sterilising, ozone generator parts are cheap and easy to buy.  They are found in things like the small battery operated fridge deodorisers, where the ozone oxidises the smelly chemicals from things like some cheeses, or fish.  They are also found in air fresheners in toilets, for the same reason.  But, one of the most common applications (at least in the UK) is for treating the water in fish tanks and ponds.  Adding small amounts of ozone will kill bacteria, viruses etc in water in which fish are kept, keeping the water clean and the fish healthy.

Ebay, Banggood etc are a great source of ozone generator parts, but the sellers often (almost always!) misrepresent what they are selling and fail to provide anywhere near enough information to be able to use their parts without some experimentation.  Hopefully the experiments I’ve done may avoid the need for others to find things out for themselves.  The first thing neeeded is a good quality stainless steel tubular ozone generator unit, together with a matching high voltage power supply.  I bought a unit from Banggood, in China.  The unit I purchased was the result of having bought several units and tried them, and this is without a doubt the best and easiest to use:  http://www.banggood.com/220V-5GH-Water-Disinfection-Treatment-Suite-Ozone-Generator-Quartz-Tube-p-1076913.html?rmmds=buy

If that link doesn’t work any more, look for units that look like this and are rated for 5g/hour of ozone production:

This unit was fitted into a metal box, with a cooling fan (it gets hot in use) and 10mm polyurethane tube was used to connect the ozone to the non-return valve on the venturi injector (this tubing has to be ozone resistant, as does the non-return valve – check that the NRV uses Viton seals).

There is a 12V power supply in the metal box, to run the cooling fan and also to power a timer relay, that comes on for 20 seconds whenever the unit is powered on (it is switched on by the submersible borehole pump pressure switch).  The power from this timer relay operates a 12V solenoid valve that blows waste water and sediment from the base of the aeration and ozonation tank, to keep it clean.  This short burst at the start of every pump cycle has no effect on the household supply, as there is a non-return valve between the aeration tank and the main pressure vessels, so the pressure vessels carry on supply the household supply for this 20 second cleaning period.

The main problem with running an ozone generator on air is that any moisture in the air both reduces the amount of ozone produced and generates small amounts of nitric acid, from a reaction with the nitrogen in the air.  This is not really enough to be harmful, but it’s undesirable, so I decided to make up an air drying unit to feed the ozone generator with dry air.  This significantly improves the performance of the generator and will make it more reliable and less likely to suffer internal condensation (a problem I had with an early prototype).

The air drier was easy to make, using a standard, fairly cheap, 10” water filter housing, together with a reusable cartridge insert that was intended for use with carbon granules.  By filling the cartridge insert with silica gel, I found that I could make a very effective air drier, and by using a clear filter housing, together with colour-indicating silica gel, I can see when to change the drier cartridge and regenerate the old one (regeneration is easy, just put it in an oven set to 100 deg C for a couple hours and it will be ready to use again).  I’ve found that a single cartridge lasts in excess of six months, and may well last a lot longer, as the one in use shows no signs of turning blue yet (the colour-indicating beads turn blue when they need regenerating and are orange when they are still OK).  This is what a filled filter cartridge insert looks like, these can also be bought on ebay, as can the indicating silica gel beads:

This is fitted into an upside down mounted, clear, water filter housing, like this:

There is one small problem created by the flow resistance of the length of pipe from the venture to the ozone generator (I used 10mm polyurethane, as it’s relatively ozone resistant), the flow resistance of the ozone generator itself and the flow resistance of the air drier unit.  Adding an air pump before the air drier was the solution, but after some experiments I discovered that it is vital that the pressure be kept low.  If the pressure in the ozone generator chamber exceeds about 0.3 bar, then the corona discharge starts to reduce, and by around 1 bar it has stopped completely.  Luckily I managed to find a reliable and low power large aquarium pump that is oil-free and delivers a maximum pressure of 0.18 bar.  This is a near-perfect match to the flow and pressure requirements, and delivers just enough pressure at the venturi end to open a sensitive non-return valve (needed to prevent water back flow when the borehole pump and ozone generator system is off).  This is what the pump looks like:

Low pop-off pressure non-return valves were used to isolate the pump from the air dryer and also in-line with ozone generator output, in addition to the standard high-pressure NRV on the venturi, to ensure that the air in the pipes and the ozone generator was always kept dry.  Alloy NRVs, modified to use silicone rubber seals (also ozone resistant) were used.

Both the pump and the ozone generator are powered from the borehole pump circuit, so they only run when the borehole pump is running, the rest of the time they are turned off.

Venturi injection unit

Next I needed to make up the venturi injection unit.  There are commercial units available, ranging from the non-automatic flow control Clack U1202 for around £140, including delivery and tax, like this:

Through to a version with an automatic flow regulator (which is what I needed) for around double the price (it’s $250, but probably ends up being over £300 with shipping and taxes).  That seemed an awful lot of money for a bit of machined PVC, and in the photos above I spotted a part I recognised, an injector venturi that’s used in all Clack water softener valves (it’s the white thing secured with a screw in the right hand photo above).  I went looking around on the Clack website and found this photo of their range of injector venturis:

This also gave me the part number for the white one!

A quick phone call to GAPS Water Treatment and one was in the post for a few pounds (they keep them all as spares for water softeners).  Once it arrived I measured it up, discovered that it flowed about 0.5 litres per minute at the sort of pressure drop I had and that it would create plenty of suction over the whole operating range.  All it needed was a housing to hold it and a sensitive non return valve (one that would open with a fraction of a bar of pressure) to fit on the ozone/air inlet side.

I bought a brass ½” BSPF tee (one with three ½” BSPF threaded outlets), a ½” BSPM to ¼” BSPF threaded reducer for the non-return valve, a ½” BSPM brass “iron to iron” connector, a 15mm compression to ½” BSPF adapter and a 15mm to ½” BSPM adapter and I was ready to do.  The only part I had to physically make was a bit of 15mm OD brass, machined up to fit inside the tee, with bored holes to suit the diameter of the O seals on the venturi injector.  A 6mm hole bored in the side of this allowed ozone/air to reach the suction point.  This is a cutaway drawing of the thing, without the non-return valve fitted, that shows how water under pressure comes in at the bottom, with the venturi sucking in ozone and air from the left hand side and the mixed water, ozone and air exiting from the top:

This is what the completed ozone injection side looks like, with all the parts annotated (the 8mm LDPE pipe has been changed for orange 10mm PU pipe and the sensitive non-return valve has been replaced with a stainless steel one with Viton seals since this photo was taken – ozone is definitely corrosive!):

There is a Y screen filter in front of the venturi, with a pressure gauge so I can keep an eye on the inlet pressure (it’s usually around 10 bar when the pump is running and drops to the tank pressure with the pump off).   The Dole Valve automatic flow regulating valve is the shiny thing on the left, and most of the water flows through that branch.  The ozone/air feed pipe is the white 8mm LDPE pipe (later replaced wit PU pipe) and the highly reactive air/ozone/water mix comes out at the top tee and mixes with the bypass flow.

Reaction or aeration tank

The water needs time to react with the air and ozone, around 30 seconds to 1 minute is enough to fully oxidise anything in the water, and there is also a need to allow the excess gasses to escape, or else the water ends up full of bubbles.  After leaving the top of the venturi injection unit, the water/gas mixture flows to a 63 litre capacity reaction, or aeration, pressure vessel.  This is a relatively cheap pressure vessel intended to be used as part of a water softener or deionised water system, again available as a spare part, complete with head fitting, from GAPS Water Treatment.  I modified the head fitting by drilling and tapping a ¼” BSPF threaded hole in the top, so that I could fit an 8mm dip tube, connected to an automatic air vent.  This maintains a small air/ozone pocket at the top, into which incoming air/ozone/water is sprayed, via a grille that is a part of the head fitting.  The head fitting has a long rigid pipe, with a strainer at the base, that takes the water outlet from the very bottom of the tank.  At the house maximum water demand this tank retains water for around 2 to 3 minutes, more than enough for the complete oxidation reaction to take place, and far longer than is needed for the ozone to kill any bugs.  Most of the time the tank will hold water in contact with the air/ozone mix for a lot longer than this, as the water flow rate will rarely exceed about 13 to 15 litres per minute.  This is a cross section of the tank (it’s the left hand blue cylinder in the previous photo):

Here’s a photo showing the top end of the tank, with the optically operated pressure switch that controls the borehole pump switch on and switch off pressures:

The water from the bottom of this tank feeds two parallel connected 300 litre accumulators, via a 22mm non-return valve and they then feed water to a backwashing aquamandix and sand filter (the right hand blue cylinder) that has a Clack control valve that backwashes the filter at around 2 am every fourth day, to wash out all the accumulated oxides.  Water from the filter feeds two supplies, both with non-return valves.  One is an outside tap supply, feeding external taps that also have dual non-return valves, the other supply runs under the slab and up into the house, where it feeds a 100 litre accumulator then a water softener, a 5µ water filter and a UV disinfection unit as a backstop in case anything isn’t killed by the ozone, or if anything breeds inside the sealed storage accumulators.  The final item inside the house water system, that has proved to be essential, is an in-line Spirovent de-aerator.  This removes all the very tiny micro bubbles of air/ozone that remain in the water, and stops the water coming out of the taps looking like milk.  It also stops these tiny air bubbles from interfering with the ultrasonic flow meter in the Sunamp PV, which is primarily why I fitted it.

The water quality from this system is excellent.  The water going in is very smelly (from the hydrogen sulphide) and contains 50% more iron that is allowable.  The water that comes out has been tested and has no significant contaminants at all, in fact the lab reckoned it was better that the water from most of the water companies in terms of the very low levels of metals and sulphides, particularly.  It also had no detectable bacteria, which isn’t really that surprising given the double disinfection used.  I could probably take the UV unit out, as I’m sure that the ozone is more than enough to keep the water safe, but I’d already fitted it before I added the ozone treatment, so it’s easier to leave it in than to take it out.



posted July 2 2016

Absolutely fascinating.

It’s very easy to see why people struggle to get borehole supplies up and running satisfactorily given the effort you have expended in resolving all of the issues you faced. Are you able to  put a figure on how much you have saved by doing this all yourself rather than employing a specialist company to do everything on your behalf?

What are your ongoing service and maintenance costs likely to be, as I assume you will need to keep on top of it / monitor what’s going on?

The big question, how would you rate the treated water from your borehole vs mains water as a drink in its own right, and for making a cuppa?



Posted July 3 2016

Amazing! That’s a lot of detail. I’m glad I can use mains supply. I’ll have to get my borehole working now so I can have my water analysed just out of interest.



Posted July 3 2016

On 02/07/2016 at 23:18, Stones said:

Absolutely fascinating.

It’s very easy to see why people struggle to get borehole supplies up and running satisfactorily given the effort you have expended in resolving all of the issues you faced. Are you able to  put a figure on how much you have saved by doing this all yourself rather than employing a specialist company to do everything on your behalf?

What are your ongoing service and maintenance costs likely to be, as I assume you will need to keep on top of it / monitor what’s going on?

The big question, how would you rate the treated water from your borehole vs mains wateronas a drink in its own right, and for making a cuppa?


Most of my effort was a direct consequence of the lack of knowledge in the UK.  Had one of the two US guys I was emailing been over here he’d have had a system installed and running perfectly in a day, using off-the-shelf parts, as soon as he had dipped a couple of test papers in the raw water and seen what needed doing to it.  He wouldn’t have added the ozone, because really that’s a bit of over-kill on my part, but would have used an off-the-shelf Clack or Microniser air injector in the pump line and just let it pull surrounding air in when the pump was running.

The problem for me was that, AFAIK, no one stocks any of this stuff in the UK.  The price of the Clack automatic flow control air injector is $250, plus shipping, plus import duty and tax, for a bit of machined PVC with a flow control washer and one of their venturi injectors.  The cost to me of making the same part was around £10 in plumbing fittings and an offcut of brass bar, around a fiver for the Clack venturi and around £30 to import the Dole Valve from the USA (I bought it on Ebay).  I paid around £8 for the special non return valve, so all together the home made injector system cost a bit under £55, and I have the advantage of being able to replace any component cheaply if need be.  The imported valve would cost around £250 to £300 by the time I’d paid the shipping, import tax and duty, I suspect.

The reaction tank, complete with head unit, riser tube and 3/4″ BSPF ports, cost around £130, delivered.  It’s a spare for a water softener, or deioniser used by window cleaners, so there are several sources for them, but I’ve found GAPS to be the most reliable.

Had I realised that aeration was the answer, I’d not have chosen the Aquamandix and sand filter I have, but would have gone for a smaller unit, using Turbidex filtration media.  The filter I have cost around £650 delivered (inc VAT) but if I was doing it again I’d go for a smaller Turbidex filter at around £450 inc VAT, which has a higher max flow rate and far better filtration (1500 litres per hour versus 900 litres per hour for the filter I have).  It also uses a lot less backwash water, as Turbidex is easier to clean.

 I can’t be sure of the costs, but I was quoted £2,800 plus VAT for a basic backwash filter installation, and frankly there’s less than a day’s work in putting the whole system together, even if you have to run the backwash drain around 20m, as I did, to get it to a soakaway.

Maintenance costs come down to replacing the UV tube every year (around £30) and rinsing out the 5µ filter at the same time.  A replacement filter when it can no longer be washed clean is around £10.  The rest of the kit has no maintenance, just checks to make sure nothing has broken or failed.  I have spares for the ozone generator,  as it made sense to buy a couple, rather than just one.

The treated water tastes a lot better than tap water here, and makes much better tea.  Much of that is down to it being a lot softer and not having any chlorine in it.  It has no smell or taste all, whereas our water at home always has a slight smell of chlorine as it comes out of the tap.



Posted July 3 2016

Phenomenal detail as ever Jeremy. Did you talk to any pump and well suppliers from this side of the water. Well drilling is very common here but that said all the equipment come from the states.



Posted July 3 2016

After following your borehole thread ( equally fascinating ), I’d like to say thanks again for the incredible detail and effort in that post 🙂

The Venturi was the bit I couldn’t grasp, but now it’s crystal clear.

( Also good to see some old school soldered copper 😉).

The only bit that’s left me scratching my head is the recirculating circuit via the Dole valve. Surely that re-introduces already ozone ‘airated’ water back into the ozone injection tee inlet, so in essence the water is getting a double dose, or an infinitely increasing dose of ozone depending on how much it recirculates?



Posted July 3 2016

Yes, I did talk to a lot of drilling companies, but here they seem to specialise in just drilling the hole and dropping the liner and pump in, then leaving the water treatment, if needed, to another company.  It seems the majority of boreholes are drilled for farms or industrial purposes, where there may not be a need for treatment.  On my mother’s farm the (very old – probably Victorian) borehole produces iron-rich water (it’s in Cornwall, where all the ground water is acidic and often rich in a cocktail of dissolved metal compounds).  When that was in use the water was pumped to a large brick-built above ground water storage cistern, standing high in one corner of the farm yard (it’s still there).  This cistern had an open top, with just a ventilated cover to keep animals out, and used to naturally oxidise the water over a period of days.  When I last looked in it there was a thick layer of orange ferric oxide on the bottom.  My guess is that when it was in use it would have been periodically emptied and cleaned out with a shovel.  Ferric oxide is dense, so settles quickly in water.

I also spoke to a few water treatment companies.  Most were unhelpful, with the sole exception of GAPS Water Treatment.  They were very helpful, but being in Rochdale meant they weren’t really able to come down and advise directly.  The local advice I did get was deeply flawed or it was clear that the company just didn’t understand water chemistry.  The majority of boreholes used for water supplies around the south and south east of England are into chalk, where the water is pretty much free from all contaminants except calcium and magnesium carbonates, from the chalk.  The only treatment needed is usually a water softener and perhaps a UV unit to be safe.

I found no one with knowledge of iron removal, and this was supported by the view of the Environmental Health Officer who came to sample our water for official public health analysis in April.  She was very interested in the iron removal system, and said that they frequently had to condemn drinking water from around our area because of the high iron content, and consumers were always asking for advice on how to reduce it, and she didn’t know of any local companies that could help.  She now has my contact details, as I’ve offered to give advice, as the system I’ve built reduces the iron in the water from 480 ppm as it comes out of the borehole, to less than 10 ppm (the minimum resolution of the lab test – it’s probably zero!) after treatment.  The recommended safe limit is 200 ppm of iron in drinking water.



Posted July 3 2016

On 03/07/2016 at 10:47, Nickfromwales said:

After following your borehole thread ( equally fascinating ), I’d like to say thanks again for the incredible detail and effort in that post 🙂

The Venturi was the bit I couldn’t grasp, but now it’s crystal clear.

( Also good to see some old school soldered copper 😉).

The only bit that’s left me scratching my head is the recirculating circuit via the Dole valve. Surely that re-introduces already ozone ‘airated’ water back into the ozone injection tee inlet, so in essence the water is getting a double dose, or an infinitely increasing dose of ozone depending on how much it recirculates?


Thanks Nick.

Nothing recirculates because there is a big pressure differential whenever the borehole pump and the ozone generator are running.  With the pump running the area below the Dole Valve and the injector venturi is sitting at around 10 bar, whereas the area above them is at between 3.4 and 4.5 bar, depending on how full the accumulator tanks are downstream.  This means that water is always flowing up the pipe above the venturi into the lower branch of the top tee, and water at the same pressure is also flowing in to the side of that same tee.  Arranging it like this ensures good mixing at the tee, as there will naturally be a lot of turbulence created by the incoming water from the Dole Valve inlet at the side, just because it’s at 90 deg to the flow.

What’s not shown is that the riser pipe connects to a length of 25mm PVC pressure pipe, with what was a clear section (this is 16 bar industrial water pressure pipe with bonded joints, not waste pipe!).  The idea of the larger bore pipe was two fold, to get some expansion that would reduce the local pressure and aid aeration and to allow me to see whether the aeration system was working, by looking for loads of bubbles in the water (it did this very well for a few days, until the inside of the clear pipe went brown from the rust sticking to it…….).  This is what it looks like, with another view of the annotated photo with a line showing the pressures in each half:

The other PVC downpipe, the large bore flexi and the sloping pipe with the gate NRV, is the waste drain from the backwashing filter, plus a manual emptying ball valve for the aeration tank, so I can empty it out for servicing (it siphons itself empty when the ball valve is opened, as the outlet pipe goes right to the bottom of the tank).



posted July 3 2016

So the Dole valve is there ‘in case’ the differential changes? Eg water isn’t always flowing through it? I just thought the ozone T would have been after the recirculating bypass created by the DV not before it. Got me thinking on a Sunday morning anyway 🙂



Posted July 3 2016

No, the Dole Valve creates the pressure differential across the venturi, by restricting the volume that would flow if it wasn’t there and was just an open pipe.  The pump will easily deliver 30 litres per minute or more, so the Dole Valve restricts the volume flow when the pump is running to a set flow rate.  The attached pdf shows how it works, but it’s very similar to the flow restrictors fitted to showers and taps to reduce flow rate, just better engineered and a lot more robust (in fact, fairly typically American!).

Dole Valves

The Dole Valve allows a constant 9.5 litres per minute (really 2.5 US gallons per minute) to flow around the bypass loop as long as there is a pressure differential across it of between 15psi and 125psi (1.03 to 8.62 bar).  In practice the lowest pressure across it is when the pump is just about to turn off, which is about 5.5 bar (10 bar –  4.5 bar turn off pressure) and the highest pressure across it is when the pump first turns on, at the lower limit of 3.4 bar, and is about 6.6 bar (10 – 3.4 bar turn on pressure), so it regulates flow pretty accurately.

Without the Dole Valve loop the pressure differential would be very high across the venturi (the pump stalls at around 20 bar, IIRC) and would be over the 16 bar working pressure rating of the pipe or the 12 bar working pressure rating of the fittings.  The flow into the tank would be tiny, about 1 litre per minute (the venturi will flow at a higher rate when the pressure is higher, because it has a fixed nozzle diameter).




Part Forty One – Hot Water At Last!

This forty first entry was published originally by JSHarris on the 21st November 2015 and received 1,244 views on the closed forum

After battling with a stomach bug for over a week, I finally managed to get the Sunamp PV in place and installed.

Installation was generally exceptionally easy, with only two areas that caused some challenges. The first was manhandling the sheer weight of the unit up stairs. It isn’t very heavy (around 75 kg) but it is small and very dense, meaning a two man lift is the bare minimum. The second challenge was getting at the pump vent plug when commissioning it. It’s set inside the top of the unit but very close to some adjacent pipe work, so a very marrow key is needed to get in and open it up – there isn’t enough space for a dumpy screwdriver. I happened to have a flat key that was intended to fasten the mandrel sockets on my hole punch set, and that proved ideal, so a suggestion is that such a key could be provided as a bleed screw tool.

Installation was simple, just connect the pre-heated warm water pipe to the cold inlet pipe at the top, connect the supplied thermostatic mixer valve to the centre hot water outlet pipe and attach a tundish and drain to the overflow pipe. The unit does not require a tundish, just a drain, as it only has a very small water capacity, so doesn’t fall within the Part G3 regulations (meaning DIY installation by a suitably competent person is fine). I fitted a tundish simply to give a visible indication if the PRV operated, as my drains are all internal and otherwise not visible. For the sake of £5 for a tundish it seemed daft not to fit one.

The thermostatic mixer is set to 50 deg C at the moment and the outlet connects directly to a 9.6 kW electric in line water heater that is set to come on at 42 deg C. This means that, for as long as the Sunamp PV can provide water above 42 deg C the electric inline booster heater won’t operate and waste electricity.

The electrical connections are very simple. The Sunamp PV comes with a 4 core heat resistant cable and is wired to earth, neutral, switched live via and isolator and switched live via an isolator and the PV diverter and bypass system.

Water is fed to the Sunamp PV via a plate heat exchanger that is fed with incoming cold water. The incoming cold water also feeds the cold side of the thermostatic mixer valve, to ensure that there is a high temperature differential to keep it regulating well. The plate heat exchanger can pre-heat the incoming water, typically to between 20 deg C and 30 deg C, which reduces the amount of heat energy the Sunamp PV needs to provide.

Here are some photos of the completed installation:



Having plumbed it and wired it, I had to commission it according to the MI’s. Really very easy, except for bleeding the pump. Turn on the water and check for leaks, waiting a while to be sure. Keep the power off. Unscrew the top lid, remove some foam insulation and taking care to not damage the vacuum insulation panels down the sides, insert a suitable tool into a very narrow gap and bleed the air from the circulating pump. I’d have liked to have taken photos of this bit, but was a bit concerned about giving away Sunamp proprietary information, so refrained. The pump is easy to get at, but has the water heater case and pipes running very close to where the shaft vent plug is situated. I couldn’t get enough purchase with a coin in the slot and there wasn’t space to get a dumpy screwdriver in there, so I first resorted to a small 1/4″ socket set with a wide screwdriver bit. This didn’t work as there’s not enough room to get more than about 1/10 turn at a time. After pondering for a while, I remembered that I had a metal hole punch kit with just the tool in it.

It’s the rusty thing at the bottom of this photo. After a bit of fiddling this did the job and with some kitchen roll placed under the pump to catch the drips the air was soon bled out OK.

Nest was to switch the power on and check the status lights, then switch the PV diverter to boost for 20 minutes to partially charge the Sunamp PV. When charging there is a very quiet hum as the circulating pump drives water past the slim inline heater and through the thermal storage cells. BTW, the internal design and layout is very neat and tidy, and looks to be extremely well engineered – none of the scrappy untidyness you see in a typical combi boiler.

After charging for 20 minutes and checking that the indicator lights were all correctly showing the status, I drew off a few litres of hot water. I have to say that the unit works extremely well, providing a high water flow rate (I could detect no difference between it and the old thermal store when the shower was running) and water at a surprisingly high temperature after just a 20 minute charge.

Since then I have left it running 24/7 and it is reliably charging solely from excess solar PV. We’re not drawing lots of hot water off yet, so I have the boost timer turned off, but in all respects is seems to meet or exceed it’s specification. One very interesting thing is that the case stays cool. It’s the right height to sit on, yet one doesn’t get a warm backside unless the pump has recently run to draw off hot water or charge the unit (the pump and pipework are near the top of the unit). I shall take some thermal images next week, and add then to this post, but the services room is remaining cool and there is no obvious indication that this little box is storing 5 kWh of thermal energy.

So far I’m very impressed indeed, and feel that there is a definite market for this device, in addition to it’s intended market as an adjunct to a combi boiler, perhaps together with some peripherals similar to mine to better suit it to a low-energy house wit no gas or oil hot water system.


ProDave 21 Nov 2015 03:44 PM:

 Interesting about the circulating pump running when the unit is charging.

 Does that come on automatically when it sensed input? And what sort of threshold, i.e would it come on on a dull day then say only 100W of spare pv is going into the unit?


 jsharris 21 Nov 2015 04:00 PM:

 From what I can tell (bearing in mind that I’ve not been sat next to it all the time) it seems that the circulating pump switches on as soon as the first pulse of excess PV is detected, and this also turns on the “PV detected” LED (the second one up from the bottom, the bottom one being “power on). There seems to be a pump over-run time, where the pump carries on running for a short time, in the anticipation that there will be more PV energy along soon. A system of internal non-return valves keeps this circulation wholly internal, so the water only runs through the heating element and the thermal storage cells.

 I’m guessing that if excess PV doesn’t occur again for some time, then the pump turns off. When I took those photos on Friday the unit was fully charged, having had a pretty good day. The lights on the side (from the bottom up) are “power on”, “PV detected”, “Charging” and “Flow detected” (when hot water is being drawn off).

 There’s no indication in the manual of the threshold, but the pump is a very low power unit, only used to circulate water around a very small circuit inside the unit, so probably draws no more than around 20W or so.


 Sunamp 25 Nov 2015 07:12 AM :

 Hi Jeremy,

 Congratulations! Sorry its taken a few days to pick up on your report.

 We at Sunamp are extremely happy that you like our product and appreciate its design and build. Thanks very much for that.

 I see no problem with you publishing pictures of the hydraulic assembly in the top of the unit. Just don’t try taking a heat battery cell apart!

 Your problems with the bleed valve are well understood and appreciated, as is the “dense mass” handling issue, and I’d like to share our plans for dealing with them. We are in progress to a V1.5 design with revised and compacted hydraulics. This new design does two things that are beneficial to the above issues:

 The bleed valve should be easily accessible. No need for a special tool with the V1.5 (sorry it wasn’t ready for you – and props for your improvisation!)

  • The smaller hydraulic block lifts in and out – its mounted on push-fit flexible hoses. Then you can easily remove the heat battery cells (assuming the unit is cold and fully discharged at the time), and hence move each part separately. Nothing then weighs more than ~30 kg. Then re-assemble at point of install.
  • Additional improvements are planned to include:
  • Choose from 4 locations where the hydraulic connections enter and exit: Each end and each edge of the back.
  • An accessories catalogue – we’ll take your system components into account on this for non-gas properties.
  • I’ll get back to you and ProDave on the more technical questions abut thresholds ASAP.

 Again, really appreciate the success you’ve had and the fact you have taken the trouble to report it very thoroughly.

 Best regards

 Andrew Bissell, CEO, Sunamp Ltd


 jsharris 25 Nov 2015 08:55 PM:

 Thanks for the comments, Andrew. The Sunamp PV continues to work exceptionally well, I still cannot get used to the fact that, unlike the thermal store it replaced, it doesn’t seem to leak heat and always feels cool to the touch.

 The bleed valve was nothing more than a bit awkward, and not really a significant issue. I’m aware than some combi boiler integral pumps are self-bleeding, with a built in auto vent, so that may be an option.

 The idea of moving parts separately sounds great for those that need to fit the unit upstairs (as we have).

 I’ve yet to run the unit out of capacity, despite running 20 minute showers, as it seems that the combination of preheated water plus the fully charged Sunamp PV, plus the ASHP delivering around 5 to 6 kW is more than enough to deliver a couple of hundred litres of hot water. I doubt that the inline booster heater I have will be needed. It’s set to 42 deg C, with the TMV on the Sunamp PV output set to about 45 deg C, and so far the inline booster hasn’t ever come on.

 Some ASHP manufacturers make a hydronic unit that is very similar to the plate heat exchanger and flow switch I have made up. It might be worth looking at making such a pre-heat add-on at some stage for the Sunamp, as then you’d have a system that would be well-matched to any low energy home tha has an ASHP and a PV installation. It may not be a big market yet, but if we continue to try and push people towards building low energy homes then such a combination would be a pretty good hot water solution.