Norwich has one of the country's highest number of office-to-flat conversions under planning laws which say developers don't need council permission, figures show.
Last year, 438 properties in the city were converted from office to residential use, data gathered by the Local Government Association (LGA) has revealed.
And figures for the county show the rest of Norfolk miles behind - with just nine office properties converted to residential use in Great Yarmouth in 2018-19 and none in any other council areas.
Figures for 2017-18 saw 69 properties converted from offices to flats in Norwich, one in Broadland and one in Breckland.
While 161 conversions took place in Norwich in 2016-17, and 19 in 2015-16, with none anywhere else in the county in either year.
Planning laws known as permitted development rules mean owners wanting to convert their properties into homes from offices do not have to submit planning applications to the local authority - meaning they are not subject to council's affordable housing quotas.
Karen Davis, Labour councillor, said she would like to see Norwich city council introduce an Article 4 directive - which would clamp down on permitted development.
But she said many of the office conversions in Norwich were being used as accommodation for university students, and said: "These places are expensive. They are not affordable for students."
She added: "What I don't want to see is really poor quality flats in old offices.
"They have done it in Harlow where the conversions are so appalling that they have created dangerous ghettos - I don't want that to happen here."
Nationally, the LGA calculated that of 54,000 new homes built since 2015, more than 13,5000 affordable homes could have been lost under permitted development
Office conversions amounting to 6pc of all new homes nationally and 48pc in Norwich.
David Renard, housing spokesman for the LGA, said there were "serious concerns" over the issue of permitted development.
He added: "The rules result in the alarming potential loss of thousands of desperately-needed affordable homes.
"Planning is not a barrier to house-building, with councils approving nine in 10 applications.
"It is vital that councils and local communities have a voice in the planning process and are able to oversee all local developments."
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