Developer Freshwater appealed after Camden Council refused planning permission for seven flats under a new mansard roof on the block in Howitt Close, Belsize Park, in August 2022.
The 1930s block, off Howitt Road, was designed by architects Henry F Webb and Ash and is a non-designated heritage asset (NDHA).
Councillors said the design, height, materials and undue prominence of the new plans would compromise the building and harm the character and appearance of the street and Belsize Conservation Area.
Freshwater submitted revised plans in October 2022 that have yet to be decided. Camden has put a decision on the new plans on hold until a public inquiry to determine the appeal had taken place.
Following a hearing and site visit on July 4, a government planning inspector dismissed the developer’s appeal.
In a report published on September 21, inspector Jonathon Parsons identified the effects on Howitt Close as a heritage asset and the character and appearance of Belsize Conservation Area, and daylight and sunlight in surrounding streets as the main issues.
He said that based on site visit observations there would be no significant loss of
daylight or sunlight.
Turning to Howitt Close, he described the building as having “its own identity and attraction” among surrounding Edwardian terraces.
Although Historic England declined to list the building, said its flat roof and architectural features make it “distinctive.. albeit in a subtle way”.
Mr Parsons said that while mansard roofs are a feature of the area, the “bulky” proposal’s height, extent and “overly large” dormer windows would make it “dominant and ‘top heavy’” despite being stepped back.
He criticised a “striking” new facing material and clay tiles that would “visually overwhelm” features that are “integral part” of Howitt Close.
He said Howitt Close’s flat roof and eaves help to distinguish it from other buildings and contribute to its “variety, significance and special interest”, adding that the roof extension copied a predominant feature in the area and would reduce its individuality.
Citing the policies of the 2021 London Plan, which he said requires “high quality design, respecting local context and character, (and) the preservation, and where appropriate, enhancement of heritage assets, including conservation areas.”
The inspector concluded that the plans should be dismissed, writing that while they would result in “significant” housing, economic and environmental benefits, they were outweighed by the harm to the significance of Howitt Close as a heritage asset and fail to preserve the character and appearance of the conservation area.