What's the latest experience on EWI cost, EPS with acrylic render, incl forming around windows, cills already in place? This would be glued (no mechanical fixings) to
a) sound existing roughcast render
b) new OSB3 wall sheathing
c) new OSB3 over-rafter sheathing, unrendered.
Done by main contractor already on site, no allowance for his site set-up, scaffolding (already in place), all drain, RW etc alterations accounted elsewhere.

And ditto for blown-in Warmcel between studs and rafters (plasterboard under-lined).
Done by visiting specialist, and AFAIK they apply a flat fee for a minimum m3 volume, thereafter per m3 - what is that minimum?
Anyone found the problem I've had - refusal to supply unless a certificate of condensation-performance can be submitted, for the proposed construction?

Of course I'm talking about my favourite timber framed, Warmcel filled, EWI'd wall (and sloping-ceiling) roof construction, which my WUFI studies years ago showed functions better with no VCL, than with a VCL, even an 'intelligent' VCL - which is too tough a nut for insulation suppliers, and now the new breed of outsourced Building Regs plan checkers, to swallow.

I have the WUFI 'proof' in the form of comparative graphs plotting moisture content round the seasons, at key points thro the wall sandwich, but suppliers and now BI's, it seems, don't feel safe, or haven't the time, to study same and draw conclusions.

They want a 10-page document which 'looks like' what someone like Warm Associates or GBS might produce (tho neither are willing to do that for third parties), giving chapter and verse on all the legislation (like a BBA Certificate does), justifying the choice of WUFI default assumptions, the regional weather file etc input, and at the end ticking a tickbox. That's how they know it's a 'skilled professional', tho there's no such qualification for doing WUFI studies. Plus I'm not actually allowed to call myself 'Architect' and don't carry indemnity insurance, which no-one seems to care about anyway.

Or else a supplier's BBA Certificate including drawing of the same wall buildup - which none do AFAIK.

Except perhaps for Viking House of this forum https://viking-house.co.uk/timber-frame-house.html , which has diverged a bit from our one-time common method but still AFAICS has no VCL.

Last job with EWI was 12 months ago;
- 110m2
- 120mm Graph EPS
- mech fixings into stone
- coloured acrylic render, with window banding
- £170m2 (inc VAT, scaffold, site mobilisation)

Not sure if that's any use to you. It was double that for the rock wool bats, which can be required if there are adjacent fire rating issues, esp if you are onto a timber frame, as stone/noncombust substrate helps it meet some of the fire breakout regs.
Didn't have an issue with the dewpoint calc, as I do my own, and submit for approval for the building warrant.

Interesting you're practicing without Prof Indemnity. Hope someone doesn't decide to come after you, and take your house. Mine is £15 a month for £1M. Would they find a loophole not to pay out on a claim? Probably :)

I'd say your deducts look a bit high, maybe more like £120/m2 ex VAT.
I did all the prep work (drains, leadwork, soffit mods, etc) so they were purely stater-brackets, GEPS supply and fix, basecoat/mesh/render, clean-up and removal of waste.

You mentioned no mech fixings. I have a niggle in my mind that there is a BReg requirement for mech fixings and pull out tests, but I wouldn't swear to that, and don't have time right now to look for it

I'm sure the dewpoint software I use isn't as good/accurate as WUFI, but it does the job in terms of ticking a box that I'm already pretty confident about.

Your PI approach is very logical, though I'm a bit more risk averse, and worry that the costs of any battle to prove that it really wasn't my fault, might be high. Has never happened yet, and don't expect it to, but as society becomes more litigiuos, and everything that happens must have someone to "blame", I sleep a little easier, even if it's a false sense of security

Mostly 1 storey, one gable 2 storey.
Cost correction, £170/m2 ex VAT
Quick check re. board fixing, the substrate surface roughness was high, being stone, hence the need for mech fixings. The"system" docs and the struct engrs required the fixings, not BRegs. My bad. A smoother substrate (up to 10mm), would be fine with adhesive only (system manuf install instructions would state, as you mention)

Posted By: stonecoldEPS over roughcast sounds like it's going to end up with air bubbles in it/air gaps, and possibly condensation with it.

If there's a likelihood of gaps then some criss-cross lines of foam just before the EPS is applied should fix the problem? I don't think there's condensation risk on the inside of EWI?