ADLIan

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

See also new Approach Doc L due next month-insulation for intermediate floors with underfloor heating.

There are 2 types of energy assessor: On construction. Primarily to show compliance with building regs so must be able to understand drawings, building regs, building technology and many pages of full sap documentation. Can offer lots of advice on energy efficiency, build efficiency, cost effectiveness etc, etc. As part of as built assessment the epc is done. Cost £100s per property. Domestic. Use rdsap and undertakes ‘survey’ of property. Lots of box ticking. Cost £35 per property, do 10 a day including travel??? Make your own mind up where the expertise is. For disclosure I’m ‘on construction’ but leaving as red tape, evidence gathering (photograph all parts of the build process please) will mean I’ll spend 90% of my time chasing information, that is probably not available, rather than doing assessments and advising clients

The reflective breather membranes (and reflective AVCLs) can give a useful reduction in the U-value but only if they face onto an unventilated airspace. When used behind cladding with a ventilated airspace behind most of this benefit is lost and there is unlikely to be any improvement in the U-value

Assuming concrete/medium density block on both sides then acoustic performance will come from the mass of the wall. Adding mineral wool or dense plasterboard will add little, if anything, acoustically.

@Iceverge As a start you need to get copies of BS EN 10211 (calculation methods) and BR 497 for the conventions used when undertaking linear thermal transmittance calculations. You also need to know the correct inputs into THERM and what to do with the output value (which is not automatically the psi-value unless THERM has changed recently). It is not a simple process!

Sorry but that THERM model is wrong. The lintel, jambs and cill should be modelled separately effectively ignoring the window. I've not used THERM for some time but in the past it did not give the psi-value directly - the output needed more number crunching to arrive at the psi-value. Whilst the psi-value may be low in this instance I doubt that it would be negative.

In a masonry cavity wall the thermal resistance of the residual cavity is set at 0.18 m2K/W.

Differences in the acoustic absorption make little or no difference to the overall acoustic performance as it is insignificant compared to the effect of the plasterboard, studs, quality of workmanship……. The Canadian document I seem to remember listed 100’s of different combinations of insulation, timber/metal studs, plasterboard thickness, No of layers etc. The type and density of mineral wool made no difference; thicker wool giving a slightly better performance.

The above does not apply to multi foil insulation. Here the manufacturers normally quote a total thermal resistance of their product based on the resistance of the core material plus the resistance of a low emissivity air space on both sides. It is the additional battens that can add to the thickness of the roof (or wall) and add to material and labour costs.

Denser does not equal better - this is something pushed by Rockwool for many years. The Approved Docs show a minimum density of 10 kg/m3 for mineral wool as an acoustic absorber in walls and floors. Someone posted a link on here some time ago to some very extensive research, I think done in Canada, that showed all mineral wool effectively does the same job and it is the use of denser plasterboard, double layer of plasterboard, acoustic studs, resilient bars etc that will improve the acoustic performance. Attached is an article from Knauf who make both glass wool and stone wool products. Don't waste your money on ever denser Rockwool! 592690867_KnaufAcousticDensityArticle.pdf