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SAP CALCULATIONS
SAP calculations are the UK government's official system for calculating the energy performance and carbon emissions of residential homes. The data output from a SAP calculation is used as part of a building warrant application and demonstrates how the proposals comply with the requirements of Section 6 of the Domestic Technical Handbook.
Typically SAP calculations are required for new build dwellings but occasionally the SAP assessment can be used as a tool to demonstrate the performance of a domestic extension where the dwelling is relatively new. Along with compliance repaort, an output from a SAP assessment is an EPC (Energy Performance Certificate). The EPC provides an energy efficiency rating on a dwelling's running cost and the environmental impact.
Depending on a client's requirements for their new home, SAP ratings usually sit between 81 -95, that's Band A or Band B. But with the introduction of some low, or zero-carbon technologies an Energy Efficiency rating of +100 can be achieved.
U-value calculations work out the rate of transfer of heat through a thermal element, such as a wall, floor or roof.
Calculated U-values are required to demonstrate how the proposed insulation envelope meets the minimum backstop values as noted under Section 6.2.1 of the Domestic Technical Handbook. They are required for both new buildings and work to an existing dwelling.
Some software packages used to calculate U-values will also carry out a condensation risk analysis.
U-VALUE CALCULATIONS
Psi-VALUE CALCULATIONS
A Psi-value is a measure of the rate of heat loss through a junction, where thermal elements meet eg. external wall and ground floor
The heat loss through these junctions is referred to as non-repeating thermal bridges. These non-repeating thermal bridges can form up to 25% of the total fabric heat loss. With this percentage being so high it is critical extra care is taken to detailing these junctions to minimise the heat loss and also accuratly calculate the heat loss through these junctions so the SAP assessment produces a more accurate modle of a dwellling's performance.
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