Building on top of 1908

The mansion block on Weymouth Street was finished in 1908, at a time when the doctors of Harley Street wanted to live a few minutes from their consulting rooms. It was built in red brick with stone dressings, five storeys high, with a flat roof that for more than a century held nothing but water tanks.

In 2016 the freeholders asked an architect, Miriam Cole, whether the roof could hold more. Westminster’s planners had one firm condition: the new storey must not be visible from the pavement opposite. Cole set the penthouse back from the parapet by almost three metres and kept its height below a line drawn from the far kerb to the top of the old cornice. The space between the parapet and the new walls became the terrace.

The building work took two years. Steel was lifted in by crane on Sunday mornings, when the street could be closed, and the residents below stayed in their flats throughout. The new walls were built in a red brick made to match the original, from a works in Leicestershire that still fires bricks the same way.

Inside, Cole wanted the two floors to feel like one house rather than a flat. The stair is the clearest example: a single run of pale stone that rises through a double-height opening, lit from a rooflight above. From the bottom step you can see the sky.

Most people who walk down Weymouth Street have no idea it is there. The only way to see the penthouse from outside is from the top of a building on Marylebone High Street, two streets away, or from the far side of Regent’s Park on a clear day.