Setting the targets for SAP
I’ve skimmed through the newly available Tables in Appendix R of SAP 2012 and put together some thoughts on the significant targets used.
The Approved Documents for Part L aren’t quite with us, but SAP 2012 Appendix R, which provides the reference values used for producing the Target Emission Rate (TER) and Target Fabric Energy Efficiency (TFEE) is now available. These aren’t the levels actually required to pass, but they do set the target emission rate for the dwelling and also the target fabric energy efficiency level (less an adjustment of 15% on relevant benchmarks). Those elements used to generate the TFEE are marked below as (FEE).
The reference dwelling is again based on the actual dwelling, but with openings based on 25% of the Total Floor Area (TFA). This means:
- For dwellings with openings greater than 25% of TFA, it will be harder to pass.
- For dwellings with openings less than 25% of TFA, it will be easier to pass.
For the fabric of the dwelling, the references are:
- Walls 0.18 W/m²K. Designing to a poorer level will make it harder to pass overall. (FEE)
- Party walls 0.00 W/m²K. It will be harder to pass if not fully filling a party wall cavity or using a solid or structurally insulated panel (SIP) party wall. (FEE)
- Floors 0.13 W/m²K. Designing to a poorer level will make it harder to pass overall. (FEE)
- Roofs 0.13 W/m²K. Designing to a poorer level will make it harder to pass overall. (FEE)
- Opaque doors Uw = 1.00 W/m²K. This makes it generally harder to pass than people are used to. Doable but good quality thermal openings required and using a poorer achieving product will make it harder to pass. (FEE). (NB Uw is a performance level for the whole opening including the frame, not just centre-pane).
- Half glazed doors Uw = 1.20 W/m²K, makes it generally harder to pass than people are used to. Fairly good performance products required. (FEE)
- Windows and glazed doors Uw = 1.40 W/m²K (g-value of 0.63), which means a good performance emissivity is required (0.05 En); This may provide an unintended benefit to anyone entering in a good U-window, but incorrectly assuming a higher g-value (more solar gains). Hopefully accreditation schemes will start asking assessors for more evidence for glazing. (FEE)
- Roof windows Uw = 1.40 W/m²K (+ adjustment factor of 0.3W/m²K for the inclination of the openings). This is an area where it’s not always obvious what plane a manufacturer has measured the roof window in, so it’s unclear whether or not the U-window needs to be adjusted or not. (FEE)
- The Thermal Mass target is in as medium level (250 kJ/m²K); This may make it easier to achieve the TFEE for low thermal mass dwellings e.g. timber frame / Internally insulated / SIP’s dwellings and harder for high thermal mass ones. (FEE)
- Thermal bridging (FEE) – The targets set are for each junction (generally to the same level as approved details from Table K1, but several to default levels and with a few that are actually a lot tighter. Overall this will I think make it harder to pass. Possibly harder than may have been considered. Those just going ‘Default’ for thermal bridging will have to do a substantial amount elsewhere to compensate.
For other elements:
- Ventilation default is naturally ventilated – as expected.
- Air tightness for the reference dwelling is set at 5m³/m²/hr @ 50 Pa. The level below which Approved Document F suggests that mechanical ventilation systems should be considered. (FEE)
- The boiler for the reference gas dwelling is in as a 89.5% efficient, room sealed, fan assisted, modulating burner control. This may make it easier for some to pass, harder for others.
- Heating controls – time and temperature zone control is now the reference for most dwellings (with the exception of single storey, with larger living areas e.g. flats). This may make it harder, but I’m aware that the definitions of controls are also changing in the building service compliance guides, so maybe not.
- A weather compensator is now assumed for the reference dwelling (+3% boiler efficiency adjustment); So this will make it harder for dwellings not using one.
- Where the hot water providion is not specified, a Hot water cylinder default of 150 litres with a heat loss equivalent to 1.38kWh/day is set. This requires a fairly good level of insulation, but products are already in the market to meet it.
- A lighting target of 100% of fixed outlets being low energy lighting is set. This makes it harder to pass if not going to this level, but really, with the cost being much reduced and the performance much improved, these levels should be the goal moving forward.
Overall, the reference values are largely as expected, but it will be interesting to start looking at the numbers in more depth once software is available to model a few real world example dwellings.
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