ADLIan

Will depend on grade of rockwool and polyurethane assumed. Remember to include 15% bridged proportion. Should give approx U of 0.20 W/m2K. Condensation should not be a problem if care taken with the VCL & PUR not sealed though not much safety margin.

Sorry - yes it's Appr Doc F that applies

In England Appr Doc C, Section 7. Looks like BCO is correct.

Be careful with Kingspan TF solutions - in the small print in the brochure tables they often include an insulated plasterboard internal to the studs to improve the U-value.

Monarflex?

Just an excuse for bad manufacturing and poor quality control. The manufacturing spec for PUR is in BS EN 13165, among many other things it gives tolerances on board dimensions (thickness, length, width, flatness etc). A trip to any BM will show their products to be 'pushing the envelope' for these tolerances, especially thickness (100mm thick board for example should be within +/-3mm) and flatness. Remember shortly after Grenfell Celotex were found out not being entirely truthful about the fire performance and thermal performance of some of their product range.

Building Control will probably look at U-value and fire performance of external roof finish - this later requriement is down to building height and proximity to local buildings, etc. Note that Scot Regs strongly advise aginst use of cold flat roofs as do relevant British Standards

@IanLow SAP probably due to use of bulk LPG. Would be very diferent with mains gas.

There is no simple SAP estimator as it is complex with many independant and interdependant inputs. It is not particularly sensitive to elemental U-values especially at the levels you mention. Taking care with air tightness and linear thermal bridges will give better returns. For a new build built to basic Building Reg standards and gas heating you should be acheiveing a SAP of approx 80-85. As SAP is based on fuel COST your choice of heating fuel and heater efficiency will have a big impact - electric resitance heating may reduce the above figure by 10-15 points!

Appr Doc L1A does not give specfifc U-values apart from the backstop, worst case, values - this gives a lot of design flexibility. The U-values in Jeremy's spread sheet are those used in the model dwelling (Table 4 in AD L1A) used to assess compliance using SAP. Remember in Jeremy's spread sheet to always enter cavity width (cell B25) in order to give correct thermal conductivity for use later in each construction. @JSHarrisCould this be defaulted to R=0.18 which would be good enough for most instances and not be so thickness dependant. The spread sheet only gives an approximation and should not be used for Buildng Reg purposes as it does not correct the U-value for thermal bridges, mechanical fixings thru the insulation, air gaps in the insulation etc

Looks as though it must be installed by approved contractor. On timber frame the vented airspace behind the cladding system negates the effect of the insulation.

Assuming in England Appr Doc C gives maximum exposure zones for a range of cavity wall details - fair faced or render? full or part fill insulation? cavity width? etc.

Are those figures correct, MVHR reduces heat loss by a factor of 7? I can see 10-20% improvement when using MVHR provided it is correctly designed. A poorly specified/designed MVHR system can potentially increase energy use!

Depending upon the supplier you may have to cut the mitred boards on site (especially if not 45 Degree mitre). Some suppliers have mitred boards as part of their package

Suggest you check MIs and BBA certs re additional mech fixings when using adhesive or plaster dabs with foam backed boards

Foam (insulation) backed plasterboard must be mech fixed to wall (otherwise it’ll just fall off in a fire!)

Vents required at high and low level - normally eaves and ridge.

The Building Regs (Engalnd & Scotland), advice in Timber Frame Construction (from TRADA) plus other sources all refer to the use of a ventilated cavity behind render systems (on a carrier board) onto TF construction. Render on insulation on the structural frame is not recommended and has not been for many years.

As a general rule if OSB or ply sarking is used this is classed as having a high vapour resistance so 50mm vent air space required below the sarking/above insulation (even if breathable membrane used above sarking). See BS 5250.

Above diag only refers to masonry leaves not timber frame.

The EPC states a GSHP has been used so the COP (though we do not know if manufacturer data or default value used) has been accounted for.

Just a few comments on the IoW house EPC; I know the assessor and he is vastly experienced, an expert on SAP and very unlikely to have got it wrong The assessor does not list the recommendations in an EPC - these are automatically generated within the EPC software The SAP rating is a measure of energy cost. Electricity is a lot more expensive than say gas within SAP so will impact (negatively) on the rating The SAP rating is not used to assess Building Regulation compliance (which is based on CO2 emissions) Difficult to say why this house has such a low EPC as we do not have the detailed information but I imagine it is due to being all electric, the large glazed area, no air leakage test (default used) and a poorly specified/designed MVHR system (which can increase energy use!) A house can have a poor EPC (D or E) and still pass the Building Regs

The SAP rating is based on energy cost so choice of fuel has a big impact. Electricity is more expensive than gas in SAP (though impact is offset by efficiency of ASHP) so SAP/EPC score will drop.

Software I use gives a decrement delay of just over 12 hrs for that construction

Also remember that the energy conservation standard under Appr Doc L1A (assuming England) for new build is much onerous that Appr Doc L1B for extension/conversion works. Check carefully with BCO exactly what they require.