INTRODUCTION
The SAP energy rating method is the Government's chosen method for producing an energy rating for a dwelling, based on calculated annual energy cost for space and water heating, assuming a standard occupancy pattern, derived from the measured floor area of the dwelling, and a standard heating pattern. The rating is normalised for floor area so that the size of the dwelling does not strongly affect the result, which is expressed on a scale of 1-100: the higher the number the better the standard.
The full procedure is described in "The Government's Standard Assessment Procedure for energy rating of dwellings - 1998 edition" (SAP 1998), published by the Building Research Establishment (BRE), which sets out the method of calculating the rating in the form of a worksheet, accompanied by a series of tables. A calculation may be carried out by completing, in sequence, the numbered boxes in the worksheet, using the data in the tables as indicated. Alternatively, and more usually, a computer program approved for SAP calculations by BRE may be used.
THE SAP ENERGY RATING AND THE BUILDING STANDARDS REGULATIONS
The Building (Procedure) (Scotland) Regulations 1981, as amended in 1997, require all new dwellings to have an energy rating calculated in accordance with the Government's Standard Assessment Procedure (SAP). In respect of dwellings, achievement of a specified level of SAP energy rating permits reduced thermal insulation while achieving a higher specified level is one of the ways of complying with Part J.
The following apply when calculating SAP energy ratings for Technical Standards purposes -
1. The data used in calculations of SAP energy ratings should be obtained from the tables in
SAP 1998. The fuel cost data will be revised in future editions.2. When the final heating system is unknown, the SAP energy rating notified to the building control body must be calculated assuming a main system of electric room heaters and a secondary system of electric heaters, both systems using on-peak electricity.
3. When undertaking SAP energy rating calculations for designs not intended for specific construction sites (e.g. type designs) the following assumptions should be made -
a. two sides of the dwelling will be sheltered; and
b. the windows, doors and rooflights are all on the east and west elevations; and
c. the solar access factor is 1.0 (average).
4. In the case of an extension there is no obligation to provide a SAP energy rating; the fabric of the extension must, however, comply with the less demanding U-values from Table 1 to J2.2. The floor area to be used for calculating the maximum permitted area of glazing is that of the whole dwelling of which the extension forms part.
5. Where a housing development involves large numbers of dwellings it is acceptable for the worst case in that development to be identified and for a SAP energy rating to be calculated for that dwelling only.