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Flaws in SAP 'cost builders millions'

The Sustainable Building Association (AECB) has criticised The Standard Assessment Procedure (SAP) as inaccurate and says it promotes expensive technology at the expense of cheaper but more effective products.

The association has predicted this will lead to at least half a billion pounds of inappropriate spending on microgeneration technologies.

SAP predicts the energy consumption of a building but the AECB says its analysis comparing SAP with Germany’s PassivHaus Planning Package exposed flaws.

According to the AECB the system overestimates some areas of energy demand and underestimates most of them. It says this leads to inaccurate predictions which produces poorly-designed buildings, which then require investment in technologies such as photovoltaics, ground source heat pumps, solar panels, biomass boilers and wind turbines to hit targets.

The AECB outlined a number of issues which it sees as key flaws in SAP.
• It does not reward advanced energy efficient systems such as low energy lighting and appliances. This leads to designers or developers not improving outdated practices and missing low-cost opportunities to reduce carbon dioxide emissions.

• It underestimates the need for space heating energy by overestimating the heat gains from internal appliances and incandescent light bulbs. It underestimates the amount of heat that is lost through the fabric of the building. It does not assume a realistic room temperature. The net result is a colder home, a higher heating bill than the designer expected, or both.
• It gives designers little credit for making maximum use of the passive solar energy available from careful positioning of south-facing windows.

Andrew Simmonds, chief executive of the AECB said: “SAP significantly underestimates both the heating needed for a low energy house and the real benefit of state of the art energy-efficient features.

“By doing so, it is resulting in hundreds of millions of pounds being wasted on expensive renewable energy gimmicks. This misdirected investment to supply energy to an inefficient building, rather than design low-cost energy-efficient buildings with an improved-quality building envelope, can be resolved by using a more accurate energy assessment method.”