ADLIan

Does the window sit on the Sarna membrane that continues from the outside flat roof to the inside? Are you then trying to weatherproof this detail using sealant? If this is the case this detail will always be a problem and I doubt complies with Sarna recommended detailing. Would normally expect the window to be sat on an upstand with the Sarna membrane dressed up the outside of this.

Check loading with insulation manufacturer. Celotex (and probably other pur) is BBA approved for domestic type loadings only. XPS has higher compressive strength and often used in areas subject to vehicular access.

Is this new build in England? Probably OK returning the blockwork but leave space for a 50mm (min) insulated cavity closer - not ideal but will meet BR minimum requirement. Better to use 150mm insulated cavity closer and use bracket/cleat to fix window frame - may be much simpler to install too, saves a lot of time cutting and laying blocks around each reveal. Cavity closer manufacturer may offer values for linear thermal transmittance - enhanced values can be used in SAP which can be advantageous.

+1 on above. I doubt the frame material has an impact on the acoustic performance. Acoustic performance depends mainly on number of panes, glass thickness (better with 2 or more different thicknesses), gap between the panes and addition of an acoustic absorber between the panes. Remember as soon as you open a window its acoustic performance reduces to zero!

With a buried roof the slab should not be cast directly onto the waterproof membrane. A drainage layer of gravel or specialist drainage membrane should be used. Water drainage should be a 2 levels - at the level of the epdm membrane and at the finished roof surface. Specialist drain outlets are available for this. Level, flush fitting, roof lights are also a specialist product. Can’t help feeling that the roof will be forever problematic without a major renovation and correct detailing and product selection. Lots of info on internet on buried roofs or podium roofs.

15% is about right in my experience for standard stud TF (not larsen truss or I-beam). I've seen it as low as 12% but also as high as 20+%- a value mentioned by Warmshell in one of their design guides! The Appr Docs refer to BR 443 which gives the 15% bridged value. I note Warmshellinsulation has a BBA cert for a rendered external wall insulation system but it limited to masonry background. They also mention that they have an applied for BBA cert for this system on TF. It appears this goes back to 2015 and still no certificate issued. As mentioned above a similar certificate (based on wood fibre) was withdrawn or allowed to lapse a few years ago. I would still refer you to the above documents and the fact that render onto insulation direct onto TF is not accepted good practice.

Bit late to comment on this but Google ' buried roofs' or 'podium roofs' and you'll see how difficult these are to design and really need specialist input especially with your flush roof lights. Need robust design and robust materials as remedial works are difficult (=expensive). Have you arranged for drainage of rainwater from directly above the EPDM membrane? Without this I imagine the roof will be plagued with problems.

I had included the 100mm external insulation - as you say this does mitigate the effect of the TF fraction. 15% bridging is the default value and includes for the additional timbers around openings, at floor levels, corners, head & sole plates etc and is normally about right, may reduce to approx 12% if you're lucky. Bottom line is the U-value has not been produced in line with UK BR Appr Doc requirements. This is all a bit academic now as the wall is done! The important point, and where this thread started, is the requirement for a vent void behind the render system in TF walls.

An additional comment. The U-value calculation from ProDave is wrong as there is no correction for the timber frame creating a thermal bridge (normally 15% bridged proportion) and this would increase the U-value to nearer 0.16 W/m2K.

Most of the insulation manufacturers in the UK will provide a U-value and condensation analysis calculation. Some may also do the thermal response/phase shift numbers. Note that it is NOT accepted good practice to render onto insulation onto the timber frame - see 'Timber Frame Construction' from TRADA, Bldg Reg Approved Docs, TF kit manufacturers details etc. One of the wood fibre insulation manufacturers had a BBA certificate for a direct render system but this appears to have lapsed or been withdrawn. The issue is not so much condensation but liquid water penetration through the render system as referenced by Mr Punter.

They’re only the soakers ar each course of slate. Lead cover flashing (longer length, approx 1~1.5m) still needs fixing, chased into wall.

Is this new build house or extension? For new build expect U=0.15 or better. For extensions BR require 0.18 or better +1 to most of the above, especially multi foil! I would not bother with Frametherm 32 (extra cost for minimal improvement on U-val especially timbers at 400mm c/c) - go for 35 version. Fully fill the rafter space with this, breather membrane, counterbatten, batten & slate with 50mm PUR under rafter. Note this is not a warm roof. It gives a warm roof space but to be a warm roof construction the majority of the insulation must be above the rafters.

U-vals are always for the whole wall (or other element). Old cfc blown pur had lambda of approx 0.020 W/ mK but expect this to degrade considerably in this application to nearer 0.03 W/mK.

Expect U=0.43 at best, perhaps 0.45.

Normal quilt loft insulation cut to fit between timber. Leave last few feet rolled up and push/unroll into place with help of a broom. Add further layers same way if needed.

I was involved in that testing program. No real surprises from this testing compared to standard BBA recommendations, especially hit and miss issues with blown products.

Check product BBA cert. Subject to certain caveats full fill, especially at 300mm, can often be used in any exposure zone. 50mm clear cavity safer still.

Plenty of pur/pir alternatives but kingspan has a virtual monopoly on phenolic foam so expect to pay top dollar for it.

Modern mineral wool cavity batts are quite dense and rigid so the normal plastic retaining collars that slip over the wall ties will work OK. Why not just fully fill with 300mm (2x150mm) with no residual cavity? Where is the building located? Partial fill normally only needed in very exposed locations (SW England, west Wales & west Scotland) or high rise (18m or more in height) but rainwater penetration is very unlikely across 300mm full fill.

The thermal conductivity will be whatever the manufacturer states and is backed up by CE marking, the DoP and perhaps BBA certification. (Note post Grenfell Celotex were guilty of over stating both thermal and fire performance of certain products and I believe had BBA certificates suspended). The compressive strength may vary depending on application and if load bearing or not. You would need to check with the manufacturer for exact values of certain physical properties but they may not be forthcoming with very detailed (commercially sensitive?) information.

On a very simple level product used in flat roofing has to cope with temps varying from say -10 C to perhaps 80+C and the foam/facings have to be formulated to cope with this. Flooring, cavity wall and 'general purpose' PIR products will never be subject to this temp variation. (Individual manufacturers may be able to offer more detailed info on the make up their products). Bottom line is the products are optimised for the application they are made for - hence swapping products/applications or using second grade product may lead to problems.

PUR and PIR may have slightly different chemical compositions depending upon application. Flat roof products for example face much more difficult conditions 'in use' compared to say a flooring application. The facings may also be different. What you see as a 'foil' face may have many different layers from a simple single layer to 11 layers or more depending upon application. Specific products based on the above variations may also be BBA approved for a particular application. An alternative view is it's all marketing and sales hype and the products are actually the same!

@ProDave SAP energy rating is based on energy costs and these are normally increased (inflation?) in new versions of SAP so your SAP/EPC will probably remain the same. The big difference is reducing the carbon intensity of electricity (fewer coal fired power stations) so should make Building Reg compliance of all electric houses easier.

For Building Reg compliance no. You have to comply with Regs and associated SAP version in force at time of application.

@Visti Not sure what stage you are at with Building Regs but SAP10 will not be used in foreseeable future. Most likely will be introduced in next update of Part L - sometime in 2020?