The Government is aiming to impose stricter carbon emissions targets on homes from October 2013 by changing the building regs.

But industry experts have argued that the testing tool for energy performance known as SAP is too unreliable and flawed to proceed.

They also warned that few homes are even being built to current 2010 Part L standards and further changes stand to create added uncertainty for house builders about designs.

Speaking at the Zero Carbon Hub annual conference, Home Builders Federation chief Stewart Baseley said: “Given the demanding standards entailed in the zero carbon policy it is essential that we have a model of SAP that is fully and properly fit for purpose.

“Without this, builders are in an invidious position in having to design buildings they believe should deliver the necessary performance, but discovering that possibly through no fault of their own, actual performance is not what was predicted.”

His concerns were echoed by Mike Leonard, director of the Modern Masonry Alliance. He questioned the sense in pressing ahead with further cuts to carbon emissions levels in homes before there was confidence about the reliability of measurement tools.

“With very few houses built to even Part L 2010 and little or no experience of the outcomes, we should be careful not to introduce another change before we understand how the industry is meeting the existing requirements.

He said: “The SAP tool needs to be made to work properly before we move on.”

He added: “Moving the goal posts now would be a big mistake and will cause further upheaval and cost at a time where housing under delivery is the major issue.”

John Tebbit, Industry Affairs Director at the Construction Products Association, said: “One major concern that has not been resolved is the continuing saga of SAP and SBEM governance and development.

“Despite the problems at the last revision of Part L, we are yet again in the unsatisfactory position of having concurrent consultations on SAP and a Part L consultation using a not yet finalised version known as cSAP. We have made proposals for industry to take on more responsibility for SAP and SBEM development, but we need Government to take action, otherwise these problems will recur in three years time.”

Earlier this week the Government released it draft consultation on proposed changes to Part L 2013.

The proposed Part L changes set tighter carbon dioxide emission standards for new homes and energy efficiency improvements to existing homes when extensions are built.

Responses to the Government’s consultation document can be provided up until 27 April, other than the proposals related to the Green Deal where responses need to be in by 27 March.

The consultations are at www.communities.gov.uk/corporate/publications/consultations/