ADLIan

@Dave Jones you are confusing ventilation of the whole house with ventilation of roofs. Please refer to BS 5250 (yes I’m using the 2021 version, at great expense! The information on the use AVCLs has not changed). An AVCL is required otherwise you are allowing lots of moisture vapour into the construction where it will condense on the next cold, impermeable surface above the insulation.

Values for the ply deck and the roofing membrane both look low. Nearer 1000 MNs/gm for ply and 800 MNs/g for the single ply (it's a continuous membrane with all joints very well sealed). These may be sufficient to alter the CRA. Problem with WUFI as I understand is that it is incredibly complex and there are no conventions for its use.

Hybrid roofs are generally discouraged. A hybrid pitched roof is often more forgiving as a breather type membrane is used. A hybrid flat roof is not so forgiving as the waterproof layer and ply/osb deck are both impermeable. To work there must be meticulous attention to detail in installing the AVCL ensuring all laps/joints/penetrations are very well sealed. Any imperfections may lead to problems in the longer term - moisture vapour may get through the AVCL but liquid water is effectively trapped. BS 6229 gives more advice on flat roofs. In a condensation assessment a lot will depend upon the vapour resistance value used for AVCL - does it assume the vapour resistance of the membrane, (which may be massively high if it includes a metal foil) or does the value reflect a more realistic 'in use' value including imperfections? As mentioned before its possible to get the CRA to say anything you want - it's knowing if correct and realistic values have been used. Not sure an intelligent membrane would work - best check with the manufacturer and any independent certification they may have

Please read BS 5250 . Lack of an AVCL will allow moisture vapour from inside the house to pass through the insulation (or gaps if foil faced) and condense on any impermeable layer above the insulation. Even if you use a breather type membrane it may not be able to get rid of all the moisture vapour. I have seen a layer of condensation form on the underside of a breather membrane which then effectively renders it non breathable. The problem with using calculators like the one referenced is that you can get them to give any result that suits you!!

Please read BS 5250.

Cold roofs should incorporate an AVCL to help prevent/minimise air movement and moisture vapour transfer through the system - what does get through can then removed by the ventilation above the insulation.

As ProDave & Nod, staggered stud with mineral wool (no need for high density! 100 kg/m3????) between and 2 or more layers of high density plasterboard, ideally different thicknesses. PUR will do nothing acoustically.

As above, not normally good practice to have insulation at different levels in a ‘warm’ roof. Check with insulation manufacturer and ask for condensation calculation. With a correctly detailed vcl it may work. Also check MIs and BBA certificate, 38mm min thick counter battens normally required

Sorry but denser does not necessarily mean better in term of acoustics. Just about any mineral wool, at a set thickness, will have a similar acoustic absorption figure, perhaps lower than 0.4 at frequencies below 500 Hz, increasing to 0.8-1.0 at higher frequencies. However any slight difference in performance between products is lost once installed in a wall or roof - the plasterboard, tiles, slates, timbers etc having the biggest impact, swamping any difference in the mineral wool. Denser slabs may also 'couple' each side of the construction and actually make the performance worse! The only difference a slab at 100kg/m3 would make would be to your wallet!

The Building Reg classification is 'Class 0' (number zero, not letter O). This is a Building Reg classification only based on BS 476 tests - it is not a true BS 476 classification however (that only goes to Class1). I don't think Class 0 is referenced in England & Scotland Regs anymore. Most building materials are covered by harmonised European Standards (that the UK will keep post Brexit) and these do not use BS 476 but instead use the Euroclass system under BS EN 13501.

A drawing would help. Be aware that having the insulation at rafter level but with a horizontal ceiling has a major negative impact on the calculated U-value. You may think you are getting say 0.18 W/m2K but due to the correction factor it may be nearer perhaps 0.22 W/m2K!

+1 on Moonshine's info. Note that to comply with the AD E you will either have to adopt the RDs and register them with Robust Details Ltd or undertake acoustic testing on completion of the units to show that the required insulation levels are achieved. Note the insulation in the cavity here does very little acoustically as it is there to avoid cavity wall thermal bypass - standard spec is mineral wool with a density of at least 18 kg/m3

Under current fire testing regime there would be little difference in fire performance between a PUR (PU?) and PIR - something like Euroclasss D and C respectively, both still combustible.

Plus client, specifiers, cladding manufacturer, insulation manufacturer, sub-contractors, specialists.... Some of it downright untruthful, a lot of ignorance on fire testing (fueled by certain industry sectors) and a mad series of contractual relationships where everyone thought everyone else was responsible for the design.

You cannot tell the difference between pir and pur just by looking at them as they both look the same, the difference is in the chemistry. Normally a yellow/cream foam with foil, bitumen felt or glass tissue facings. The material used in packaging is expanded polystyrene, EPS, (you can normally see the individual beads that have been fused together). EPS is even more combustible than pur/pir and tends to shrink away from fire but does create molten droplets which can spread fire further. Rock and glass wool products are classed as non-combustible.

PUR or PIR doesn’t really matter as both come under the above Standard and both still combustible. Difference is in the chemistry, PIR slightly better thermal and fire performance compared to PUR but still burns..

BS EN 13165 which covers the manufacture of PUR foam was introduced in early 2000s and referenced BS EN 13501 for the assessment of the fire performance. Both Kingspan and Celotex continued to use BS 476 data (which was no longer relevant) hiding behind the Class 0 surface spread of flame rating. Note Class 0 is not even a BS 476 rating! Hence the issues at Grenfell. Finding the Euroclass fire rating for these products was not made easy simply because the D or E rating would have revealed them to be combustible. From memory the other PUR foam manufacturers did use the Euroclass system as soon as it was introduced.

It’ll be fine. Crack on. £600 extra??? No wonder we’re cynical!

Don't see what the problem is - if its OK to be used vertically why not at an angle? Only has to support itself until the ceiling finish goes in as ProDave says. Perhaps they make more money on the Metac!! I also doubt lack of BBA certification will be an issue and never had a problem with this construction as the application is covered in the Appr Docs and relevant British Standards

Also add the chemicals they (may) use to deter insects and improve the fire performance

See BS 5250. If a suspended floor it requires ventilation. At a stretch a ‘suspended’ floor could be designed to have insulation pumped in afterward but it would then effectively become a ‘solid’ floor requiring a dpm (correctly joined to dpc) and positioned to protect the insulation. Probably simpler to build it correctly. I’m sure the bba certificates for these flooring systems will require ventilation without exception.

The gshp and pv will keep the co2 emissions down but there is also a fabric energy efficiency standard and if other U-values are not up to scratch you may have problems. U=0.2 in a floor is not good. Have you had a SAP assessment done as this will give insulation requirements and fabric efficiency numbers. Does your bco have the sap numbers to confirm compliance with Regs?

Mineral wool roll or batts with a conductivity o 0.035 W/mK or better are normally rigid enough to be self supporting as ProDave says (to do with density). I think we all know of the fibreglass you refer to - probably made not a millions miles from you!!

75mm PUR sounds to be the very minimum to get through Building Regs - would expect at least 100mm and as above 150mm+. I'm not aware of U=0.20 being against any flooring requirement, 0.25 is the worst acceptable. What does your SAP report say? Normally PUR in a floor requires a dpm below and another membrane above - check with manufacturer instructions and BBA certificate install instructions

The test method for thermal conductivity accounts for thermal drift and worsening of lambda over time often found with PUR, Phenolic and XPS foams. Declared values should reflect long term lambda (20-30 years)