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This page hosts information, guidance and background materials which may be useful to those interested in renewable energy, sustainable construction and energy efficiency. If you have any questions or comments on these materials then please contact the SEAM Centre.

Introduction to SAP

Colin Sinclair of BRE has provided this introduction to the Standard Assessment Procedure (SAP), which is the UK Government's methodology for calculating the energy performance of dwellings.

Introduction to SAP

The SAP calculation is based on the energy balance taking into account a range of factors that contribute to energy efficiency, such as:

materials used for construction of the dwelling
thermal insulation of the building fabric
ventilation characteristics of the dwelling and ventilation equipment
efficiency and control of the heating system(s)
solar gains through openings of the dwelling
the fuel used to provide space and water heating, ventilation and lighting
energy for space cooling, if applicable
renewable energy technologies

The calculation is independent of factors related to the individual characteristics of the household occupying the dwelling when the rating is calculated, for example:

household size and composition;
ownership and efficiency of particular domestic electrical appliances;
individual heating patterns and temperatures.

Except where the dwelling has a fixed air conditioning system ratings are not affected by the geographical location.

What is calculated?

The indicators of energy performance as included within SAP are energy consumption per unit floor area, an energy cost rating (the SAP rating), an Environmental Impact rating based on CO2 emissions (the EI rating) and a Dwelling CO2 Emission Rate (DER).

The SAP rating is based on the energy costs associated with space heating, water heating, ventilation and lighting, less cost savings from energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given built form. The SAP rating is expressed on a scale of 1 to 100, the higher the number the lower the running costs.

The Environmental Impact rating is based on the annual CO2 emissions associated with space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies. It is adjusted for floor area so that it is essentially independent of dwelling size for a given built form. The Environmental Impact rating is expressed on a scale of 1 to 100, the higher the number the better the standard.

The Dwelling CO2 Emission Rate is a similar indicator to the Environmental Impact rating, which is used for the purposes of compliance with building regulations. It is equal to the annual CO2 emissions per unit floor area for space heating, water heating, ventilation and lighting, less the emissions saved by energy generation technologies, expressed in kg/m²/year.

Further Information

The procedure used for the calculation is based on the BRE Domestic Energy Model (BREDEM), which provides a framework for the calculation of energy use in dwellings. The procedure is consistent with the standard BS EN ISO 13790.

The Standard Assessment Procedure was first published by the then DOE and BRE in 1993 and in amended form in 1994, and conventions to be used with it were published in 1996 and amended in 1997. Revised versions were published in 1998, 2001 and 2005.

The present edition is SAP 2009 in which:

space and water heating are calculated on a monthly, instead of an annual, basis
space cooling is included
thermal mass of construction elements is explicit rather than implicit
energy used for domestic hot water has been revised
weather data has been updated
CO2 emissions factors have been updated using the latest available data
the calculation of boiler efficiency from test data has been amended
the performance of heat pumps can be based on test data
internal heat gains have been revised and a reduced level of gains is proposed for design purposes

At present the effect of feed-in tariffs has not been factored into SAP. This is under consideration and the government will consult on proposals at the earliest opportunity.

Reduced Data SAP is not being amended in this revision and RdSAP assessments will continue to use SAP 2005 version 9.83 for the time being. It is anticipated that RdSAP will be revised following the implementation of SAP 2009.

The method of calculating the energy performance and the ratings is set out in the form of a worksheet, accompanied by a series of tables. The methodology is compliant with the Energy Performance of Buildings Directive. The calculation should be carried out using a computer program that implements the worksheet and is approved for SAP calculations (BRE approves SAP software on behalf of the Department for Energy and Climate Change; the Department for Communities and Local Government; the Scottish Government; the National Assembly for Wales; and the Department of Finance and Personnel).

Further information on SAP 2009 is available here.