What are SAP calculations?

Darren Evans
June 21, 2021

Calculations carried out using the Standard Assessment Procedure, or SAP, are used to show that a proposed dwelling meets the energy efficiency requirements of national building regulations. It is primarily used for new-build dwellings, but can be used to assess the performance of extended or refurbished dwellings too.

The SAP methodology was created, and continues to be developed by, the Building Research Establishment (BRE). Government adopted SAP calculations as the preferred approach for assessing the energy performance of dwellings. Major updates to SAP tend to coincide with updates to energy efficiency regulations.

What do SAP calculations measure?

Measuring the energy performance of a dwelling requires a ‘whole-building’ approach, taking into account a variety of factors and how all of those factors interact. SAP calculations include all of the following:

  • Building fabric performance, including U-values of floors, walls, roofs, glazed elements and doors.
  • Linear thermal bridging heat losses.
  • Heating system and any secondary heating.
  • Hot water heating and storage.
  • Ventilation.
  • Energy efficient lighting.

With the introduction of Part L 2021 in England, the updated SAP 10 features, for the first time, solar PV systems, detailed information about showers and baths and waste water heat recovery.

Using the SAP methodology, the calculations resulting from the inputted data compare the energy performance of the proposed dwelling against that of a ‘notional’ dwelling of the same shape and size. The proposed emissions must match or better those of the notional dwelling.

In England, SAP is also used to compare the fabric energy efficiency standard (FEES) of the proposed dwelling to the notional dwelling. The regulated energy consumption of the dwelling must again match or better that of the notional dwelling.

When are SAP calculations carried out?

Design stage SAP calculations must be submitted as part of a building regulations application to show that what is being proposed will meet the energy efficiency requirements.

Once work on site is completed, as-built SAP calculations must be submitted to demonstrate that compliance is achieved by what has been constructed. The building control body cannot sign off the dwelling as complete without these calculations.

It is common for the design stage calculations to be carried out only when a more detailed specification starts to be drawn up for the purposes of making the building regulations application. However, there are multiple benefits to having a preliminary calculation carried out in the earlier design stages to help inform planning and layout choices.

Because SAP calculations take into account so many different factors, changing one impacts on what is required from all of the others. Setting an outline specification from the outset can help with estimating required external wall thicknesses, or the need to include space for building services, for example.

As experienced sustainability consultants, Darren Evans can work with you at any stage of your project to provide design recommendations and help to achieve compliant SAP calculations. We recommend engaging with our SAP calculation service as early as possible, to avoid any costly and unforeseen changes that may need to be made later on.

Start a conversation by contacting us to discuss your project’s needs, and find out more about the range of sustainability services we can provide.


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