Mark Greenfield

Potton were the cheapest, but are now out of the frame, so to speak - they are no longer making kits for self-builders apparently. That may explain why they were the cheapest, and the others were all very similar.

It's not expensive compared to traditional methods at all when everything is considered. Trad building can often end up costing more - try comparing a trad build with the same performance at timber frames such as MBC and you'll soon see why!

Isn't always AS easy to get the 10 year structural warranty in place. Plus, many lenders won't lend against a build system unless it comes with what they call 'third party accreditation' - ISO:9001, or similar.

Kind of; typically a Larsen truss is a complete truss (joist) fixed to the structural element, which is a bit wasteful and isn't quite as effective in terms of thermal bridging as a twin frame, but agree that in principle they're similar.

Yes - I'm familiar with twin-frame (and MBC - I'll be asking them to price for me), but I don't really want a twin-frame as it's expensive.

Seems a lot of kva to be fair; is there a mid-point?

Stick build is a nightmare for structural warranties, and even if I could get past that lenders really don't like it either. I've done a few for extensions over the years, but warranty not required. It's not a standard arrangement at all - but if you can point me to a manufacturer and installer that works with it and can give me the accreditation standards I need for a warranty and mortgage I guess I could look into it!

The problem is you don't really have anywhere to go with this I don't think - there's no competition for the Grid, so they can name their price. £15k seems better than I would have expected for a 50kva transformer to be honest, although I appreciate it's not in the budget. It'll cost you more than double that to consider a proper off-grid solution.

I don't think this build-up would meet the approval of warranty companies would it? The problem is I would have to find a company that manufactures this type of timber frame that is accredited, and of all the shows I have been to I've never seen this arrangement, so that strikes me as tricky! Out of interest, the load bearing frame element of the image would also be the service cavity in this scenario I guess - which seems great! Also, where would the racking board go as it's not shown on the drawing?

Problem seems to be the junctions; where frame meets blocks etc.

It doesn't work for timber frame construction though, I don't think?

Keen to know the answer to this too - there must be a way to mitigate thermal bridging using a standard block and beam? I saw on another thread on here, which I'll try and dig out, that someone used some insulation in the outer cavity but wasn't sure how keen building control would be on that idea.

That happens with builders too (and kitchen companies, window companies, etc etc)! There's no need to insure against it, lenders will lend - and do. Some won't, but it's a tiny amount (Coutts, for example). Buildstore provide mortgages tailored for self-build - and they even do advance stage release so you can draw-down the funds needed in advance of the work being carried out. They don't even ask for vesting certificates. It's a no-brainer; I guess the self-build market is one they want to be in. If anything, working with a bona-fide timber frame company would de-risk a build, surely? All engineering and materials accounted for, accredited manufacturers and installers, the ability to check their credit scores and so on is all possible.

Problem with stick-build is that I know my lender won't accept it. We need to provide "third party accreditation" - ISO9001 or something like that. As far as I can tell, these accreditations can only be applied to factory-made products so stick-building won't be an option. I've used stick-build for extensions before, but for my next home it's just not an option. Factory-made timber frame will also be a lot faster on site, and less dependent on weather etc.

Isoquick did the lot for you? Design, supply and installation (including all site prep work)?