New planning rules announced by the UK government will require new homes built under permitted development rights to be over 37 square metres.
The Royal Institute of British Architects (RIBA) has praised the ministry of housing for closing a "dangerous loophole".
"Minority of developers abusing the system"
New houses built under permitted development (PD), which allows existing buildings to be converted to residential without going through planning permission, will have to meet minimum space standards.
"Most developers deliver good homes and do the right thing," said housing minister Robert Jenrick.
"I'm tackling the minority of developers abusing the system by announcing that new homes delivered will have to meet space standards." Homes must be 37 square metres
Previously, homes built in converted offices could be smaller than the official bare minimum of 37 square metres for single occupancy homes.
"I'm delighted and relieved that housing delivered through Permitted Development will now have to meet the National Described Space Standard," said RIBA president Alan Jones.

"The government has done the right thing by closing this dangerous loophole and ensuring new PD housing across England will have adequate space and light ? standards that should be a given," he added.
Jenrick said that 60,000 homes have been built under PD in the past four years.
"The pandemic has further highlighted the importance of having...