ADLIan

Not sure about the requirements in Scotland but certainly the new Appr Doc L for England requires photographic evidence of a lot of the works. Failure to do so is viewed as a non-compliance with the Regs and can also impact the SAP assessment as the assessor needs copies of the photos too as part of the 'as built' assessment.

Older versions of BS 5250 on condensation always showed a VCL at ceiling level with loft insulation. In the latest version (2021) the VCL is omitted in diags but referenced in the text as an AVCL. I questioned BS on this sudden change in building physics and as Mr Punter says the main concern is mass air movement though openings/holes in the ceiling. For the cost and for a belt and braces approach I would use a VCL or duplex plasterboard.

Hi Nick - unclip those wings and fly!! My 'expert' jibe was directed to the website you linked too and certainly not a personal dig.

Sorry but that model is wrong - therefore the numbers for the psi-value (not U-value) are probably wrong too. THERM is not particularly intuitive when pulling together the basic model (in fact it's downright difficult), the numbers generated need further manipulation to generate the psi-value and the calculation must follow set conventions. Depending upon the geometry, cavity closer and position of the window I would expect a psi-value for the jamb to be approx 0.07 - 0.10 W/mK

EPS (along other rigid cellular plastic foams) has no acoustic properties - thermal yes, acoustic no. Acoustic products either have large mass or open cell structure (to absorb sound energy). Foams are all very lightweight and have a closed cell structure - just what you don't need!! The website linked above is just so wrong. Expert???????? Mineral wool is the best option for stud walls (with plasterboard both sides).

The recommendations in the EPC (solar pv, solar thermal etc) are generated automatically by the ‘black box’ behind, not by the SAP assessor

As above the tapered roof design Co are trying to get the 'balance' of insulation correct to avoid condensation issues. This can be modeled quite well using BS EN 13788 without resorting to WUFI. The are specific design issues with warm flat roofs that cover the install of the AVCL - most manufs will want this fully supported on the structural deck/below the insulation. See MIs and BS 6229.

A badly designed MVHR system can have a negative effect on the SAP outputs - if the cost (money or energy) of running the fan is greater than the energy saved.

Agree this should have been picked up as part of the BR application. Looks like BCO is treating this as a solid wall - Appr Doc C gives info on when and how this is permissible. The render is not the issue, the whole wall construction should have been assessed. Is there a BBA, or similar, certificate for the Durisol system which would give advice on maximum exposure zone? Durisol should be able to help do the exposure rating calculation (BS 8104 according to Appr Doc C). This may show lower exposure rating if in a town centre with shelter from adjacent buildings. Otherwise you may have to look at tile hanging or some other form of rainscreen/impervious cladding. Have a read of Appr Doc C and question Durisol.

Check which version of the Regs apply. Also Wales (your location?) may be different to England

Different heating zones?

Under 2021 Appr Doc L there is a requirement for thermal insulation in intermediate heated floors - not onerous however. Prior to this no thermal requirement but acoustic requirement of 100mm mineral wool.

Its also a requirement of the Building Regs & Appr Doc L to both limit heat losses from the pipes and prevent heat gain in the dwelling

BBA certs and MIs normally show use of AVCL. Is the 150mm pur all above the rafter? If so chat with Helifix as the fixing spec must resist wind uplift but also the dead load of the roof tiles and it’s tendency to slide down the roof slope. Needs specialist design to counter this especially as the tiles and battens are cantilevered away from the roof structure and the tendency to want to bend the fixings. Timber stop rails can help here. Also check with insulation manufacturer as they should be able to help

Most pur manufacturers actually make pir. A tweak in the chemical components giving pir - slightly better thermal and fire performance (but both still burn).

I’d be more concerned about fumes from the burning contents of the house (furniture, carpets, timber - including chipboard and ply. Couple of lung fulls of any products of combustion from these will kill you a long time before any insulation is involved in a fire.

Problem has been for the software developers getting their results to agree with all the BRE test cases. Elmhurst software just received approval at end of last week.

Yet another example of building control not understanding what guidance they are enforcing and policing

I don't think its that simple. Landlord safety cert is just that - a safety check on existing gas pipes and equipment. The Building Regs require something very different for the install and commissioning of new kit, My understanding is the certificate is supplied by the GS engineer via Gas Safe and then Building Control (see gas safe website).

You need the relevant BS for the definition of well and slightly ventilated. Try BS 5250 and/or BS EN 6946. In a cold flat roof the airspace should be well ventilated - this affects both the U-value calculation and the condensation analysis.

VCL is not breathable, clue is in the name and its function.

Do not install further insulation between the roof joists. Creates a hybrid roof that is not recommended by industry or BSs and greater risk from condensation.

This form of roof construction should have a VCL on top of the deck/under the insulation. This will be covered in BS 5250, BS 6229, MI's and BBA Certs. Should also have been picked up by BCO as it comes under Appr Doc C. Only real solution is to strip and replace. How is the insulation & membrane fixed down to the deck?

Buried, or podium, roof is never a good idea unless specialist advice taken. Any insulation involved (it’s a roof!)? Also potentially massive thermal bridge as roof slab becomes internal floor slab.

That table and link are 2021 version of Part L which does not come into force until 15 June 2022. From memory current standard for windows is U=1.6