More than half of family homes under construction by private housebuilders in the UK are too small, architects have said.

The typical new three-bedroom home is missing space equivalent to a bathroom while many are missing as much as a double bedroom when judged against minimum reasonable space standards launched by the government in October.

Homes outside London are the worst affected by what the Royal Institute of British Architects (RIBA) attacked as “rabbit hutch” homes after it measured a sample of new homes on 100 developments.

RIBA singled out two of the leading housebuilders as the worst offenders. From a sample of new three-bedroom homes surveyed, it found Barratt homes were on average 6.7sq metres smaller than minimum space standards and Persimmon homes were on average 10.8sq m too small – about the size of a double bedroom.

“Tiny rabbit-hutch new-builds should be a thing of the past,” said RIBA president Jane Duncan. “But, sadly, our research shows that, for many people, a new home means living somewhere that’s been built well below the minimum space standard needed for a comfortable home. The government must take action to ensure a fairer minimum space standard is applied to all new homes across the country …”