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The Government's Standard Assessment Procedure for Energy Rating of Dwellings covers the traditional SAP calculations of energy use per m 2, but also includes an environmental impact rating based on CO 2 emissions and the DER (Dwellings Emission Rate, see AJ 27.10.05). The SAP calculation can only be carried out via a computer program that has been developed by the BRE.

To this end, DEFRA has licensed the certification process to a number of acceptable companies who have all developed a range of SAP programmes that you will have to use, although none are, as yet, available.

These nine chosen companies are listed on http: //tinyurl.

com/7hcgh and include the usual suspects like the National Energy Services (or National Home Energy Rating, as it is known) and 'software outsourcing company' MVM Consultants, as well as smaller players - including my alma mater, John Potter Architect in Newcastle.

The idea behind the SAP ratings is relatively unchanged in that they are designed to assess the amount of energy used by a building without any regard for the shape, size or geographical location. Thankfully, they are also independent of the actual use to which a building's heating system is put, so we can still turn up the thermostat in the privacy of our compliant new home without John Potter sending the boys round.

In the new SAP:2005 the main alterations are as follows:

? On the scale of 1 to 100 (where 100 represents zero energy costs) you can score >100 as a net exporter of electricity;

? Thermal bridging has been included in the calculations;

? The measurement system is now kWh instead of GJ; and - Lighting energy and alternative generation sources are included.

Even though the BRE provides a six-page worksheet calculation print out, the SAP calculations cannot really be done by hand and architects will be forced to seek advice.

Page 7 retains some of the clues about how to minimise the extent of compliance. Attics, for example, should still only be included in the calculations if they are 'habitable rooms accessed by a fixed staircase'. Whether sales of loft ladders have increased is unknown.

For the dedicated, Appendix Q allows for 'new energysaving technologies that are not included in the published SAP specification.' At the time of going to press, these technologies (which must have been approved and be included on the web page bre. co. uk/sap2005 to be acceptable) are not yet listed but can be used to offset other energy sources by adding the kWh/year and CO 2 emissions generated by the new technology (including fans, motors, pumps, etc) and subtracting that notionally generated by a principal heating system. Manufacturers' data can take precedence over notional values.

In general, my advice is to read the first 25 pages (especially the helpfully highlighted changes from SAP:2002), skim pages 28?37 and 41 and forget the rest. You are going to have to trust someone else to read, digest and perform the detailed work on your behalf, I'm afraid.

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