This is a dumb question, after all these years. We here think a lot about wall 'sandwich' build-up details, model them in WUFI etc, for interstitial condensation risk, air tightness etc. And lately, for example, I've found insulation suppliers such as Warmcel refusing to authorise their distributors to supply their product unless it's being done to a certified detail/design. Strangely, I can find nothing in Building Regs that makes similar requirement - which Part is about this, if not C (ground/rain) moisture, F vent/condensation, L thermal? No search term I can think of, produces refs to such details, tho I know manufacturers publish sample construction details, get BBA Certificates etc, on use of their product. So, question is, what different kinds of sources are there, for such detail/designs that can be used as evidence of approvability, if not certifiability?

Posted By: fostertomsuppliers such as Warmcel refusing to authorise their distributors to supply their product unless it's being done to a certified detail/design.

Maybe due to their insurance provider insisting on it?

Posted By: fostertomwhat different kinds of sources are there, for such detail/designs that can be used as evidence of approvability, if not certifiability?

Good question...

Possibly an issue with fire regs.

Since Grenfell, it has become increasingly difficult to specify timber frame projects using generic detailing.

Changes proposed push towards using details (and materials) exactly as specified in fire testing. Essentially this means every combination of materials needs to be tested and the specifications followed otherwise you won't get sign-off and insurance.

i.e. you can't substitute one manufacturer's fire-rated plasterboard for another manufacturer's fire-rated board, even if it has the same - or better - properties unless that exact combination of materials has also been tested.

Utter madness, but 'Rectum Protectum' is the order of the day.

The company I work for has just released an updated STA Fire-in-use pattern book for our structural products after extensive, (expensive) testing - we've essentially been told it is worthless unless followed to the letter...