1.1 A new dwelling must be built to a minimum standard of total energy performance. This is evaluated by comparing calculations of the performance of the ‘actual dwelling’ against calculations of the performance of a theoretical dwelling called the ‘notional dwelling’. This must be carried out both at the design stage and when work is complete.
The notional dwelling is the same size and shape as the actual dwelling and has standardised properties for fabric and services. The full properties of the notional dwelling are set out in the Government’s Standard Assessment Procedure (SAP) for energy rating of dwellings.
1.2 The energy performance of the notional dwelling is described using the following metrics.
a. The target primary energy rate, in kWhPE/m2 per year: this is influenced by the fabric and fuel.
b. The target emission rate, in kgCO2/m2 per year: this is influenced by the fabric and fuel.
c. The target fabric energy efficiency rate, in kWh/m2 per year: this is influenced by the fabric only.
1.3 The target primary energy rate, target emission rate and target fabric energy efficiency rate for individual dwellings must be calculated using the Government’s Standard Assessment Procedure, Appendix R. The standardised properties are summarised in Table 1.1.
NOTE: For an up-to-date list of approved software, follow the link to SAP 10 at:
https://www.gov.uk/guidance/standard-assessment-procedure.
Buildings that contain multiple dwellings
1.4 For a building that contains more than one dwelling – for example a block of flats or a terrace of houses – an average target primary energy rate, target emission rate and target fabric energy efficiency rate may be calculated as an alternative to individual target rates for each dwelling.
The floor-area-weighted average of the target primary energy rate, target emission rate and target fabric energy efficiency rate for all the dwellings in the building should be calculated using the following formula:
[(target primary energy rate1 × floor area1) + (target primary energy rate2 × floor area2) +
(target primary energy rate3 × floor area3) + …]/ (floor area1 + floor area2 + floor area3 + …)
1.5 The average target emission rate should be calculated using the formula above but replacing target primary energy rate with target emission rate.
The average target fabric energy efficiency rate should be calculated using the formula above but replacing target primary energy rate with target fabric energy efficiency rate.
1.6 Calculating an average target primary energy rate, target emission rate or target fabric energy efficiency rate for separate buildings on the same site is not considered a reasonable method to show compliance.
District heat networks
1.7 For a dwelling that is connected to an existing district heat network, the notional building used to calculate the target primary energy rate and target emission rate can use the same primary energy and CO2 emission factors for the heat and hot water delivered to the dwelling as used in the calculation of the dwelling primary energy rate and dwelling emission rate. All other aspects of the notional building, except wastewater heat recovery, should remain as outlined in Table 1.1.
NOTE: For a dwelling that is connected to a new district heat network, the notional building used to calculate the target primary energy rate and target emission rate should follow the specification shown in Table 1.1.
Notional dwelling specification
1.8 The full notional dwelling specification used in the Standard Assessment Procedure is given in Appendix R of SAP version 10: https://www.bregroup.com/sap/sap10/. The notional dwelling specification is summarised in Table 1.1.
Table 1.1 Summary of notional dwelling specification for new dwelling
