SAP Ratings

The Building Research Establishment (BRE) developed a national standard for rating the energy efficiency of dwellings - the Government's Standard Assessment Procedure  (SAP) - which was launched in 1993. In order for an organisation to be fully authorised by the Department of the Environment to offer SAP ratings it must have its software approved by the BRE and its procedures registered under quality assurance standards BS EN 9002:1994.

Factors Affecting a Dwellings Energy Rating

In its introduction to the SAP procedure the Government quotes the following regarding important factors in the SAP and therefore energy efficiency:

"The rating obtained from following the SAP depends upon a range of factors that contribute to energy efficiency:

The rating is not affected by factors that depend on the individual characteristics of the household occupying the dwelling when rating is calculated for example:

it is not affected by the geographical location of a dwelling; a dwelling will have the same rating whether it is built in Caithness or Cornwall"

Components of the SAP Procedure

The SAP worksheet for calculating a dwellings energy rating progressess through eleven sections which require user input or are calculated from previously obtained figures:

1. Dwelling Dimensions
2. Ventilation Rate
3. Heat Losses
4. Water Heating Requirements
5. Internal Gains
6. Solar Gains and Utilisation Factor
7. Mean Internal Temperature
8. Degree Days
9. Space Heating Requirements
10. Fuel Costs
11. Energy Cost Rating [SAP]
12. Carbon Index [CI]

SAP and the Building Regulations in Scotland

The current technical standards for Scotland were brought into effect in March 2002. The section dealing with energy is Part J entitled Conservation of Fuel & Power (Part L in England) These regulations "require all new dwellings to have energy rating calculated in accordance with the Standard Assessment Procedure (SAP)" In essence there are three methods in use within the Regulations which can be used to ensure that dwellings have "provision for conservation of fuel & power"

Method 1 - Elemental Standards

Method 2 - Target U-Value Standards

Method 3 - Carbon Index (i.e. extension to SAP)

In addition to these methods, which are conditional. there are areas relating to the maximum area of glazing and doors allowed as a function of floor area. The SAP 2000 software for calculating SAP ratings provides for compliance of Methods 1 & 2 and additionally for the conditions set for glazing and door areas.

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