Thermally Efficient

SAP 2012 and Appendix R

‘Standard assessment procedure’ (SAP) is adopted by government as the UK’s methodology for calculating the energy performance of buildings and ultimately demonstrating compliance with Part L Building Regulations.

Appendix R of SAP 2012 provides a specification for a notional dwelling of identical proportions and dimension which provides the target for the CO² and the FEES. If a dwelling is built conforming to Appendix R values it will achieve the CO² and Fabric Energy Efficiency targets to comply with Part L.

Appendix R requires a lintel Psi value of 0.05 W/m.K, which the Hi-therm+ lintel achieves (see the psi value comparison chart).

The Importance of Psi Values

The thermal performance of a lintel is expressed in terms of a Psi value i.e. linear thermal transmittance which is more commonly referred to as ‘thermal bridging’.

The increasing focus on thermal bridging means that materials specifications and component selection need to be carefully considered as part of the overall compliance strategy to meet Part L.

Poorly performing products and SAP calculations using default Psi values are increasingly penalised, the only way to improve the SAP calculation at this stage will be to over compensate in the design by improving other areas of the fabric such as higher performing insulation, wider cavities or bolt on renewables ultimately increasing the build cost.

To design efficiently for Part L, it’s important that energy assessors use independently calculated psi values or manufacturer calculated psi values providing they have been calculated by a trained person using specialist thermal modeling software. Keystone’s technical support team are trained and accredited to provide specific psi value calculations free of charge that can be directly input in to SAP calculations.

Talk to our Technical experts to find out how Hi-therm+ could save money on your build specification.