Part Twenty One – Putting In The Insulation

This twenty first entry was published originally by JSHarris on the 20th November 2013 and received 2,149 views on the closed forum

After a delay caused by the wrong sized window having been supplied, the guys from MBC turned up in force this week to finish the interior. Once again I have to say how impressed I am with the way these guys work, they do probably twice the work in a day of most British builders I’ve seen, and barely stop, even for a tea break.
All the framing of the external walls is now clad with airtight panelling, with every joint taped, the windows and doors taped and extra foam squirted in to ensure a good seal behind anywhere that could have a gap. Here’s an example of the taping around a window:

The foam around the window frame to house frame has been cut back square and then overlapped with special tape that is stuck to the very edge of the window frame and folded back and stuck to the window casing in the frame. This bit of tape will be hidden behind the plasterboard and window cill, so won’t show when the house is finished. There’s also tape over every joint in the panelling and over the airtightness membrane that runs around the ends of the joists. If we don’t get a good air test result on Friday I shall be surprised, as the attention to detail in getting the basic structure airtight is very good indeed.

One surprise I got was just how much insulation is needed to fill the walls and roof. The house is stacked to the ceiling with bales of compressed Warmcell cellulose insulation:

The insulation is made from old newspapers and magazines, you can see little flecks of colour in it here and there. I can’t help but wonder how many millions of ground up words we’ll have inside our walls and roof, not to mention all the ground up page three images! Every major world event in the past few years could be recorded on broken down specks of paper in our walls and roof, as could the announcements of joyous events, like births, or the passing of loved ones in the obituary columns. To lighten (and lower) the tone there was a suggestion that some of the coloured bits may even have come from confiscated porno magazines!

The insulation is blown in by a (very quiet) German machine, that works by remote control. Here’s a shot of it being fed with a bale of insulation:

The insulation first gets broken up by a stirrer at the base of the big red drum, then blown under a fair bit of pressure through the flexible hose and into the wall or roof. The hose is a tight fit into the hole and the insulation gets blown into every nook and cranny inside the frame, ensuring there are no uninsulated voids. Although the thermal resistance of blown insulation like this is poorer than that of foam boards, in practice this is negated in part by it being a full fill system, with no chance for any gaps or voids due to poor cutting of the insulation boards, or someone forgetting to foam a joint. It does mean having thicker walls (there’s 300mm of insulation in our walls and 400mm in the roof) but that seems a small price to pay for the performance and guaranteed insulation integrity.

Anyone who saw the old Grand Designs programme, where Kevin McCloud got the timing wrong when having a go at blowing in this type of insulation will know that the result of stopping the machine too late is a snowstorm of paper in the house (or, in his case, in his face). This machine made that far less probable, as it worked by remote control. There’s a radio link between a control box that the hose operator has, and the machine that could be at the other end of the house. This makes stopping the fill just as the pressure increases at the fill hole fairly easy. The guys only had one small blow out, but unfortunately it was one of the fill points near the box that held their lunch (you can just see the box in the second photo above). The result was that they were picking bits of ground up newspaper from their sandwiches, tea bags etc – all adds to the flavour I guess, and certainly put a bit more fibre in their diet.

The final shot is a close up of the hose in one of the fill points:

Although the insulation runs all through the wall (from one end to the other practically) from just a single fill point, as the system has enough pressure to blow the stuff several metres through the wall, the guys drill holes at the top of each section (every 400mm) to ensure that the insulation is filled right to the top and under the right pressure. Packing it in like this avoids settlement over time, as the stuff wants to slightly expand out from the space it’s in. The fill holes are all covered with tape to seal them up.

The other main even of the day was a visit from the building inspector, who wanted to see the insulation going in and take a note of the U values for each element. So far I’d not been on site for any of the building inspector’s visits, but as I’d had no questions about the build, and had only heard that building control were content, I was keen to meet the chap and try and see if he had any nagging worries. As far as I can tell, some builders like to keep building inspectors at an arm’s length, giving them the minimum amount of information needed to get each stage signed off. I’ve never been clear how many stages of inspection we’d have, or what the inspector might be concerned about, so meeting him today was going to be interesting.

As I suspected, he’d not seen another build like this, so wasn’t familiar with a lot of the techniques being used. What I didn’t expect was the degree of enthusiasm he expressed, not just for the way the house had been designed and was being built, but for the high standard of workmanship, and particularly the attention to detail from the MBC team’s work. We had a long chat about the generally poor standard of building in the UK, and he asked a few questions about cost versus performance of our house. When I told him the price of the house (as a package from MBC), plus the cost of the windows, roofing and cladding, he reckoned it was on a par with a house built to just meet building regs. I suspected this might be the case, but it was nice to hear another opinion. He also agreed that many new houses probably weren’t actually meeting building regs in practice. I related tales of a couple of sites we’d visited, where it was clear that corners were being cut in terms of airtightness and insulation integrity by the builders, and he agreed that he’d heard rumours that developers would get the first house in a development built to pass inspection, then take short cuts with the rest as they knew that only one house of each type new development would actually be inspected. This tale also appears in Paul Buckingham’s excellent paper on the poor standard of UK building, that can be downloaded from here:…energy-savings/

At the end of our chat, the building inspector asked if I would mind hosting a meeting of some of his colleagues at the site and give them a talk on the design and construction philosophy and technology, illustrating the difference in performance between a house built like this to one built to just meet the current requirements of Part L of the Building Regulations. He is going to talk it through with his manager and feels that if he can get agreement from him they might treat such a visit as a part of their Continuing Professional Development, with the hope that it might help influence the design and construction of better new buildings in the region. As well as building inspectors and colleagues from building control, he also suggested inviting some planning and conservation officers, given that our house is in a fairly sensitive location, in planning terms.

I have to say I was a bit taken aback by this idea at first, but have decided that it can only be a good thing if it happens. I can’t help but feel that, as a lowly self-builder, giving a talk on house design, construction and performance to a group of building professionals ranging from Building Control Officers, through Planning Officers to Conservation Officers is a little bit daunting! If it comes off I will report back on here as to how it went, warts and all.

I’ve posted before on the forum the difference in heating requirement alone for our house, as designed, versus exactly the same house but built to just meet the insulation and ventilation requirements of Part L of the building regulations. As it’s pertinent to the chat I had this morning with the building inspector, and the points made by Paul Buckingham in his paper, I thought it worth re-posting them here, side by side, but note the different scales (the scale on the building regs min is 10 times greater), for comparison:

In simple terms, our house needs just more than about 1/3rd of the heat input in any given condition than a house built to the minimum standards of Part L. Given that it probably hasn’t cost any more to build to get this standard, and given that the true heating energy input (as distinct from “free” passive heating input from occupants) will be closer to 1/4 (or perhaps less) of the heating energy input for the same house built to the minimum requirements, I don’t think this is a bad outcome. The test will be if the house does actually work as designed.


 ProDave 20 Nov 2013 06:58 PM :

 Excellent progress.

I’m familiar with construction like this having worked with our local eco house builder. The tape used is this stuff…uct/sicrall-60/ And it really is very very sticky indeed.

Even a humble timber frame house can be made airtight with this stuff.

Do they only seal the “fill” holes with tape, or does a solid panel go in that then gets taped to seal it?

Any concerns about fire hazard with “old newspaper” insulation?


jsharris 20 Nov 2013 07:24 PM :

 That tapes the stuff – incredibly sticky, as you say. It does stick a heck of a lot better to the green surfaced airtight panelling than it does to plain timber, though. I’ll find out what the green stuff is, as it’s ideal as an airtight layer, as it has a very smooth, semi-matt, sealed surface.

The fill holes are only sealed with tape, as per the Warmcell instructions. Warmcell supply circular tape discs to go over the fill holes, but two bits of that Siga tape seems to do a better job, and the Siga stuff has a proper certification as a sealing tape (AFAICS the Warmcell circular patches look to be just standard sticky back plastic).

The ground up newspaper is treated with a fire retardant and also an insect repellent (borax, I think).


 oz07 20 Nov 2013 08:36 PM :

 Poor sods eating newspaper dinner!


 jsharris 20 Nov 2013 09:08 PM :

 It wasn’t just newspaper, I think it was bread, butter, ham, cheese and mayonnaise with just a smattering of ground up newspaper!


 joiner 21 Nov 2013 07:01 AM :

 Excellent, J.

You couldn’t handle Shropshire’s lot as well, could you?


joiner 21 Nov 2013 07:09 AM :

 And just picked this up…



 jsharris  21 Nov 2013 07:43 AM :

 Dave, re: that Telegraph article, I’ve added a snippet to your thread on this, about a proposal I heard of yesterday whereby developers would be able to build homes to a low CfSH level yet get them certified to a higher level on payment of an offset fee to the local authority, which would, supposedly, be used to fund projects that would reduce the carbon level in the region down to that from houses that had a lower energy consumption.

The end result is that we’ll be building homes that need far too much energy to heat, home owners will face higher energy bills than they need to, but the local authority gets some cash, the developers save some cash and the energy companies make more money. This seems a good strategy for everyone except the home owners, who end up paying two or three times the cost on energy than if the original plan to make all homes meet CfSH level 6 was implemented.

If you’re David Cameron this probably looks like a good way to circulate more cash and reduce the subsidies paid to local government, so one can understand why it’s being considered, even if it is, by any reasonable measure, barking mad.


 SteamyTea 21 Nov 2013 08:39 AM :

 When is the air test being done and why is it done after the insulation in fitted?


 jsharris 21 Nov 2013 08:52 AM:

 Air test is tomorrow morning, after all the insulation has been blown in behind the airtight layer. That way it tests the integrity of that layer after all the holes for pumping the insulation in have been made and sealed. I suspect the insulation itself also helps with airtightness. Warmcell sort of mention this in their blurb (see here: Because the insulation completely fills all the voids between the inner and outer skins of the house, and because it’s pretty dense when pumped in at the set pressure, it helps to seal things up as well, I think.

I’ll be over there with my air flow meter (one of these: http://www.testolimi…rmal-anemometer) tomorrow checking for leaks during the test.


 wittenham 21 Nov 2013 01:30 PM :

 thanks for the update, Jeremy. I have all this to look forward to in the coming weeks. and our space is full of bales of insulation at the moment, as well.



coopers 22 Nov 2013 08:14 AM :

“I can’t help but feel that, as a lowly self-builder, giving a talk on house design, construction and performance to a group of building professionals ranging from Building Control Officers, through Planning Officers to Conservation Officers is a little bit daunting!”

JSH, you probably know more than that lot put together!


jsharris 22 Nov 2013 10:04 AM :

 Thanks for the words of confidence, Suzanne, but they are SUPPOSED to know more than us self-builders!

On a slightly different topic, we had the air test this morning (at 07:00 would you believe!) and got a pretty good figure, well within the PassiveHaus Institute limit of 0.6 ACH at 50 Pa. The actual figure was 0.49 ACH at 50 Pa, with a lot of the leakage coming from the lower part of the French window – I measured flow rates of between 0.2 and 0.5 m/S around the centre of the floor level joint with the house de-pressurised to 50 Pa – and a little coming from the key holes in the door locks (about 0.1 to 0.2 m/S flowing through them with the keys removed). Bearing in mind that a 50 Pa pressure differential is equivalent to a wind speed of 9m/S blowing directly at this door (around 20mph, or force 5), this seems OK, but I’ll try adjusting the door seals a bit to see if I can get it lower (I have my own home made blower fan that I can use to depressurise the house and go around adjusting doors and windows to try and reduce this a bit).

As a direct comparison with Building Regs requirements (which use a different system for measuring air permeability), our house would need a permeability figure of less than 1300m³/hour at 50 Pa to comply with the regulations (which are worked out on floor area, with a limit of 10m³/h.m² at 50 Pa pressure difference). The actual permeability figure in Building Regs terms at the moment (before I tweak the French window seals) is 167.6m³/h.m² at 50 Pa, so around 7.7 times better than the regs require.


 notnickclegg 22 Nov 2013 10:30 AM :

 That’s brilliant news Jeremy. I actually just logged on to give you a nudge to let us know how it went! You must be pretty pleased with that, given that it sounds you should be able to bring it even lower pretty easily.



jsharris 22 Nov 2013 11:02 AM :

 It is a good result, especially as the only leakage points seem to be around the door seals. The house frame itself is, to all intents and purposes, airtight, virtually all the leakage (small as it is) is through door seals (the window seals all seem pretty airtight).

I think that it’s inevitable that doors like French windows will struggle to get a really good seal. The need to keep the threshold low (in order to comply with the requirements of Part M for wheelchair access) mean that the manufacturers have a bit of a struggle to devise a really good seal down there. Add in that the seal has to work in the corner where two opening doors meet and it’s hard to see how it can ever be perfect.

To put this into perspective, though, when I de-pressurised our current house this summer (to test my home made blower fan) I found that our 5 year old UPVC doors were dreadful. With the house de-pressurised to 50 Pa I was getting leakage velocities of between 3 and 9 m/S around some of the seals – you didn’t need a flow meter to find them, you could hear them howling! Despite this, the doors don’t ever feel draughty, so I suspect that the 0.2 to 0.5 m/S figure I was getting at the bottom of the French window will probably be undetectable in normal use.


 wmacleod 22 Nov 2013 11:51 AM :

Excellent stuff Jeremy, very good air tightness result, the build is moving along at a good speed! Why not suggest to the council that if you are going to do a talk that they invite any self builders that have applied for planning within the last year or so as well? They’ll have email addresses for most of them so should be relatively easy and cheap for them to do. Spread the knowledge a little further on the ground as it were.


 jsharris 22 Nov 2013 12:24 PM :

 That’s a good idea! Apart from getting a bit more awareness about energy conservation in new builds, it might also give some other self-builders a bit of confidence. I certainly found the idea of managing a self build bloody daunting at first. I understood the science well enough, it was the practical stuff, like finding contractors, dealing with the utility companies, learning how the various trades work and interact with each other, that I found very daunting at first. By the time the ground works were completed I felt far more confident about managing the build myself.

A fair bit of that confidence grew from advice obtained from this forum, either directly or indirectly by the professionals here providing much-needed reassurance and guidance. If some of them lived closer to me I’d have employed them, that’s for sure, as another thing I’ve learned is that trying to always get the lowest price for everything is not a good idea, all it does is result in more cost and stress down the line when work either needs to be re-done or someone else needs to be paid to come and fix problems. Thank fully this has only happened once (so far) and hasn’t been a major issue, plus I now know not to use that particular contractor for other work on site later.


ProDave 22 Nov 2013 07:23 PM :

 A question.

Exactly how much pressure is 50Pa? I have no feel for it.

Would it be enough to suck the water out of a standard toilet or basin trap (if the plumbing was finished)?

Normally the air tests are done early on in the build and all drain pipes are capped off, but I’m just wondering if it could be done later and the water in the trap would be a good enough seal?


 jsharris 22 Nov 2013 07:53 PM :

 It’s nowhere near enough to affect the water in a trap, Dave. It’s the pressure you’d feel on your hand if you held it out the window of your car when driving at about 20 mph with no wind.

There’s no reason you couldn’t do the test at the end of the build, as long as all the traps have water in and any overflow pipes (which are a bad idea in a low energy house build anyway) are capped.

There’s no reason (at least here in England) to have an air test, either, most self-builds aren’t required to have a permeability test unless they are pretty big. I’ve made a variable speed fan unit to do rough and ready air testing, using a big car radiator fan fitted to a cheap model aircraft brushless motor and speed control unit. This gives a constantly variable fan speed (and so pressure) when the fan is mounted in a board taped over an open window.

I depressurised our current house a few months ago and was amazed at the number of air leaks. Some of them literally howled, but there were some that were invisible (like the joints between the ceiling and walls, behind the coving) that were letting in a LOT of air. All told it was an interesting (if slightly depressing) experience.


 ProDave 22 Nov 2013 08:11 PM :


I thought an air tightness test was now required. If not, it’s an expends I can do without.

Re your DIY air test, I might (when the time comes) have a go at that. How do you measure the pressure? a simple manometer? if so how many inches of water does 50 Pa equal?


 jsharris 22 Nov 2013 08:20 PM :

 The pressure measurement is a bit of a problem. Even a tilted tube manometer struggles to measure 50 Pa accurately. I have used the most sensitive pressure sensor I could find (intended for use in electronic barometers) and use it by measuring the static pressure (fan off) as a zero datum, then measuring the pressure after that and adjusting the fan to a speed that gives that pressure. By then putting the Testo flow meter in the fan flow, and knowing the fan duct area, I can then work out the air leakage rate.


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