SAP is used to calculate the energy performance of new homes, and to ensure that they comply with the Building Regulations for minimum energy performance (Part L). SAP assesses the energy efficiency of the home, that is, how much heat, hot water and light do you receive for every pound spent on fuel.
SAP assesses the cost per year to provide a home with heating, hot water and lighting, to a given standard, and expresses this per square metre of floor area. As well as the SAP rating itself, the SAP methodology also provides an Environmental Impact Rating, based on the amount of Carbon Dioxide produced by the home, and again expressed per square metre of floor area. The SAP Energy Peformance Certificate therefore shows two graphics, the first presenting the energy efficiency of the home, and the second showing its carbon dioxide emissions.
The SAP methodology is maintained by BRE on behalf of the UK Government.
RDSAP
RDSAP is also used to calculate the energy performance of homes, but it is designed specifically for the assessment of existing homes. The fact that the property is already built limits the amount of data that can be collected. Because the assessment has to be done via a visual inspection, to avoid damaging the fabric of the property, it just isn't possible to gather all the data required by SAP.
If the missing data was to be estimated (guessed!) by the energy assessor, there would be huge differences in the estimates made by different assessors for the same home. To avoid this, RDSAP includes many built-in estimates, called inferences, for all the data that cannot be gathered in the inspection. For example, the insulation levels that were originally present in walls, roofs and floors when the home was first built are inferred from the date that the property was built. So, one important data item that the assessor will want to collect is the build date of the property, and also the build date of any additions or alterations to it. Where it is possible to check if any additional insulation has been added since, such as by looking in the loft to check loft insulation, the energy assessor is able to amend RDSAP's inferred estimate with a more up to date figure.
RDSAP was developed by a collaboration between BRE and the three Authorised Energy Rating Organisations (
NHER,
Elmhurst Energy Systems and
Northgate), who at the time were authorised by Defra to issue quality assured energy ratings for homes using SAP. Each of these companies had developed their own systems for adapting SAP to suit existing homes, but each system was different. There was a need for them to come together to identify best practice in each of their systems, so that one single system - RDSAP - could be used by all energy assessors carrying out energy inspections of existing homes.
SBEM
Like SAP, SBEM is used to
calculate the energy performance of buildings, but it is only used for buildings that are not used as dwellings. Unlike SAP, the same software system is used for both new buildings and existing buildings. There are options in the software that are more appropriate for new buildings, and others that are only really appropriate for existing ones, but which option to use is left up to the energy assessor. As a result, there may be more differences between assessors when using SBEM than when using SAP/RDSAP.
A big difference between SBEM and SAP is that unlike SAP, SBEM is not concerned with the cost of fuel used in the building. Instead, it estimates the amount of carbon dioxide emissions produced per square foot of building area. This means that the Energy Performance Certificate for a building that is not a dwelling actually expresses its carbon performance, not its energy efficiency.
Another difference is that the SBEM result is then compared with the carbon performance of the same building if it had been built to the Building Regulations standards that applied in 2002, and expresses the rating as a ratio. A building that is assessed to perform better than this standard receives a rating below 100, and one that performs worse is rated above 100.
SBEM is maintained by BRE on behalf of the UK Government.
Consultation
on SAP & SBEM in 2010
The SAP, RdSAP and SBEM methods are updated every few years to take account of new developments in energy performance improvement and to improve the methods' accuracy in light of new performance data. During 2010, major changes were proposed to
the SAP & SBEM energy rating tools.
The
revised SAP, known as SAP2009, came into force in October 2010
alongside changes to Part L of the Building Regulations. The changes were intended to make SAP
more appropriate to deliver the low carbon homes now required by
Regulations, and to improve the accuracy of some aspects of the
calculation. As the changes are more relevant for new homes
being designed now to low carbon standards, Reduced Data SAP has not yet altered: RdSAP assessments will
continue to use SAP 2005 version 9.82 for the time being. It is
anticipated that RdSAP will be revised in 2011 following implementation of
SAP 2009.
SBEM, the methodology used to show compliance with Part L for non
domestic buildings, was also amended as part of the proposed changes to Part L. There was no
separate formal consultation on the changes to SBEM, as they are mainly intended to implement the proposed changes to Part L,
whilst also correcting some deficiencies of the earlier method.
You can read the statement from DECC about this consultation at DECC webpage. The consultation itself has closed, but information may still be available at SAP
consultation.
As
well as the consultation document, this site offers the proposed SAP
document, tables and worksheet, plus background technical papers on the
revised emission factors and changes to the treatment of boilers.
Further technical papers are available on request, including for
example papers on domestic hot water, and the relationship between
floor area and occupancy in SAP.