Home extensions: MPs warn of confusion over relaxation plan
The coalition has not made a "rigorous" case for allowing people in England to build larger home extensions without planning permission, MPs have said.
Ministers argue the temporary scheme will help boost the building industry.
But the Communities and Local Government Committee warned of "confusion" over the new rules and more disputes between neighbours.
The government promised a "balance" between the rights of people building extensions and those living next door.
It announced in September that the maximum length of single-storey extensions built without planning permission would be doubled from three to six metres. For detached homes the new limit would go from four to eight metres.
The relaxation, applying in unprotected areas, would last for three years, in an effort to help the construction industry, whose output fell by 5.1% in the year to October.
Prime Minister David Cameron said he was "determined to cut through the bureaucracy that holds us back".
And, in October, planning minister Nick Boles predicted the three-year period could be extended if "everybody is happy", adding that changing the law did not amount to a "crime against humanity".
But the committee raised concerns that the government's "assumptions are so tentative, broad-brush and qualified as to provide little assurance that the financial benefits suggested will be achieved".
Despite the relaxation being temporary, "the effects of the changes in terms of new development on neighbours and localities will be permanent", it added.
The MPs called for a "fresh and extensive" consultation, looking at a "range of options".
They said: "We regret that the government has failed to address or evaluate the social and environmental arguments put forward against the proposed changes to permitted development rights for domestic extensions."
They added: "If the change to permitted development rights is worth making, it should be permanent. If it is not, the change should not be made. The proposed changes need to be subject to a thorough and rigorous examination, which the consultation initiated on 12 November 2012 is not.
"Temporary changes can cause confusion and create uncertainty both at the inception of the change and in the period before its conclusion."
"We conclude that the case for the changes the government proposes to permitted development rights for domestic extensions has not been made.
"We therefore do not agree that in non-protected areas the maximum depth for single-storey rear extensions should be increased to eight metres for detached houses, and six metres for any other type of house."
Some councils have warned the scheme will be a "free-for-all". Labour also opposes the relaxation.
A Department for Communities and Local Government spokesman said: "The planning system needs to strike a balance between the rights of the homeowner and their neighbours, avoiding excessive red tape whilst still protecting local amenity.
"Our practical proposals make it easier for thousands of hard-working families to undertake home improvements to cater for a growing family and for businesses to expand and grow, and the consultation we are currently running gives people the opportunity to comment on the reforms.
"The reforms would take the majority of applications which are uncontroversial and approved out the system, while some 160,000 applications will continue to be considered through the planning system."