Carbon emission targets promised by the government for the new energy regulations have been watered down by a “sleight of hand” according to critics.

The ODPM set a target of making buildings constructed under the proposed revision to Part L of the Building Regulations emit 25% less carbon than buildings constructed under the current Part L.

However, Andrew Warren, director of the Association of the Conservation of Energy, said this was now unlikely to happen. He said: “The reduction in carbon dioxide emissions from these changes will be more like 18% rather than the 25% originally proposed.”

The row centres on the U-values, which are the measure of the heat conductivity of a building element. According to Warren, the ODPM said it was going to relax U-values for walls and roofs, but compensate for the resulting increase in carbon emissions by tightening up on thermal bridging standards.

Instead the ODPM has announced the thermal bridging standards will be the same as the existing standards.

Warren said the ODPM had made the new Part L appear tougher by substituting the current prescribed thermal bridging standard for a different figure. This “as built” figure is based on buildings that have already been completed, and in effect does not raise the standard.

There is a strong lobby of builders who are saying their standard details will have to be altered

Andrew Warren

Warren said this was the first time ever that figures for Building Regulations had been based on the “as built” condition. He said: “The government is saying: ‘Here is the law of the land but because people aren’t complying with it we will lower the standard’.”

He added that it was down to pressure from within the industry: “The reason for doing this is there is a very strong lobby of builders who are saying their standard details will have to be altered.”

The ODPM was unavailable for comment as Building went to press.