The £68.5m transformation of Manchester city centre’s iconic Debenhams building will go ahead despite concerns about an ‘ugly’ rooftop extension.

Major plans to redevelop the Rylands building to provide a new shopping arcade at street level, along with several floors of new offices, have been touted by owners AM Alpha.

It would also involve the Grade II listed landmark on Market Street getting a much-needed makeover aimed at restoring its Art Deco glory.

Debenhams, which has occupied the Rylands building since 1973, is closing its flagship store after going into administration last year, putting 12,000 jobs at risk across the UK.

A CGI of the top floor extension to the Debenhams building, as seen from Piccadilly Gardens

There are no plans for another department store to take its place, and instead new shopping, dining and leisure outlets will open in the ground floor and basement.

AM Alpha had also considered converting the building into apartments, a cinema or a gallery but office space was seen as the most sustainable long-term use of the building.

Another CGI image of the redeveloped Rylands building from Market Street

Up to 258,000 sq ft of new offices will occupy most of the vacant upper floors, as well as a 40,000 sq ft four-storey rooftop extension.

An atrium providing natural light between the second and seventh floors is also planned, along with a winter garden on the sixth floor.

But Piccadilly councillor Sam Wheeler told Manchester’s planning committee that the extension would have a detrimental effect on 15 families living in neighbouring buildings.

Coun Wheeler said on Thursday: “I think we can all admit that the box on top of the Grade II listed building is incredibly ugly.

“It has been a policy of the council for some 30 years or so now to promote city centre living, not just city centre existing.

“Each time there is a loss of habitability caused by loss of light in several apartments that does lower the livability of the city centre.”

The meeting heard that a loss of light would have a negative impact on the mental and physical wellbeing of those who would be affected by the rooftop extension.

The original Rylands Building, now home to Debenhams, on Market Street in Manchester

Committee member Councillor Jon-Connor Lyons, also a Piccadilly ward member, said the extension would ‘box in’ hundreds of residents living between Market Street and Church Street.

But Katie Wray, assistant director at Deloitte acting on behalf of AM Alpha, said the proposals would ‘restore and rejuvenate’ the Rylands building and secure its long-term future.

The vote to approve the application was passed by eight councillors, with two voting against and one abstaining.