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 U Value Calculator is 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.