ADLIan

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.

Lots of references to Code for Sustainable Homes and Zero Carbon Homes in the Fen Drayton doc. As these are both dead in the water I doubt these conditions are now enforceable. I believe JSH had a similar issue and had the condition removed.

@JSHarrisJeremy - I would refer you to manufacturers test data on this one. Insulation in floors under the DPM can also experience the same hydrostatic pressure as basement walls (unless very well drained)

I didn't want to scare monger just giving information that is freely available from EPS manufacturers. Your house will not fall down or be ejected into oblivion but the thermal performance of the EPS will be slightly worse. I do not have shares in any DPM or insulation companies. I am aware of Peripor this is one of the enhanced moisture resistance products. If the manufacturers are OK with a free draining sub base then fine.

The comparison of EPS floor insulation to swimming floats is irrelevant - as a floor insulation it has a critical technical function to fulfill over the lifetime of the building. In constant contact with moisture, say under a DPM, EPS can absorb water something like 3-5% by volume (there are some newer products with enhanced water resistance where this figure may be 2% or better - these are often coloured pink, green, blue etc to make them look like extruded poly). This moisture absorption can add between 2-4 mW/mK to the thermal conductivity of EPS. Other physical properties generally not affected hence their use as inert fill/void formers.

I assume the eps here is only acting as a ‘cushion’ so probably not

DPM required in ground floors (GF) with just about all insulation types. DPM not required on upper floors but polythene VCL/slip layer/separating layer needed with insulation under screed

Same applies to pur/pir. Again check MIs and BBA certs for use in GF

Yes eps does need a dpm under it. Check MIs and BBA certs