ADLIan

Nothing to do with SAP - its a perfectly acceptable inclusion in the U-value calculation and is covered in the U-value conventions document that supports the Bldg Regs/Appr Docs. Done correctly, to MIs, mass air movement behind the plasterboard will not occur.

Aircrete block will generally give a much better psi-value than a medium or dense block (in the same detail). In a typical ground floor/wall junction expect the psi-value with dense block to be approx 3 times higher than with an aircrete block.

Yup. But check with your Building Control Body as it it responsible for enforcement

Vertical flashing and soakers looking at tile type?

This work would fall under the Building Reg requirements (assuming England) to upgrade the roof insulation. Generally max Uval of 0.18 W/m2K (IIRC) above conditioned space or max 0.35 W/m2K above non-conditioned space. Building Control needs to be involved.

Doesn’t read well when they knock the competition, by name/type so much.

It's all in Appr Doc F in England. Do you currently have background (trickle) vents and intermittent extract fans to 'wet' rooms? If your air pressure test comes in at less than 3 you will need to upgrade this to continuous extract or a mech vent system. Get the test done and see what the result is. If you get less than 3 I am sure there 'ways' of increasing this to above 3 (open a trickle vent???). Your testing guy may be able to offer some simple 'advice'!.

Those numbers look to be the standard recommendations the SAP software generates and they are absolute rubbish - do you have a copy of the SAP report you could post? A good consultant should have the knowledge of construction technology, sensitivities of the SAP calculation and suitable cost effective upgrades.

PUR, PIR & polystyrene have no acoustic properties. Mineral wool should help here but if this is a beam supporting a wall above and bearing on another wall below flanking transmission may be in issue.

The exception is for masonry walls only - 2 leaves at least 75mm thick. Note this is only the English Regs - there is no similar exemption in Scotland, Wales or Ireland that I am aware of. Timber or steel framed construction is NOT included. The issue with a fully filled cavity (hence no cavity!) is covered by not having to seal the top of the cavity. I'm sure this guidance is based on risk and the fire 'engineering' related to single houses and fire/smoke in masonry cavity walls. I wonder if the above diagram may have been better if it called them 'cavity closers' with a nod to the thermal requirements of AD L. I note it does not use the phrase 'cavity barriers'.

AD B gives definitions of 'cavity barrier' and 'fire stopping' but not 'cavity closer'! Diag 5.3, Note 1, in the current AD B is quite specific about there being no particular fire performance requirement for the materials used to close the cavity. This note was included only in recent versions of AD B (post 2019?) and is not in the technical guidance for Wales, Scotland & Ireland. I have own my thoughts on why this was changed!! There is also no restriction on the fire performance of materials used in the cavity - mineral wool will be non-combustible, polystyrene and PUR/PIR will be classed as combustible.

If this is the case why are there so many products on the market for use around door and window openings that are based on polystyrene or PUR insulation that have no fire resistance properties quoted.

@Jammy5 you will need photo evidence of this junction. Be very careful of using an alternative (though outwardly similar) detail!!! @ETC if the detail complies with Diagram 5.3 above there is no fire resistance requirement for the cavity closer around openings so no need for CS board.

That’s the one!

SAP is not particularly sensitive to elemental U-values so hopefully OK - only your SAP assessor can give a definitive answer