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Weymouth Street Penthouses

Four new luxury apartments within an extended mansard roof over three buildings. As complex as urban surgery gets

the Conservation Area Audit stated that an extension on it would be viewed as potentially unfavourable

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Project Details




Westminster, London


The Howard de Walden Estate






Building Services



Mark Winnington
Vivien Loseby
Jonathan Holt


David Butler

When our client approached us regarding this monumental mansion block, they hoped to convert the roof into luxury penthouse apartments. Whilst we were confident we could deliver what they wanted, the parameters in which we were to work were less straightforward.

The building, while not listed, was considered a Building of Merit and the Conservation Area Audit stated that an extension on it would be viewed as potentially unfavourable. In addition, the building had an office and 27 active flats which we had to ensure remained as undisturbed as possible during the construction process, all while replacing all the services and lifts, and ensuring all existing properties, including the adjoining buildings, retained their original access to light. Further complexity lay in the roof, which would not support the additional flats and would require a new floor.

We took an organised and functional approach to this complicated brief. We harnessed technology to carry out detailed research regarding potential clashes between the new services to be installed and the structure. We mitigated the disruption by seuqencing construction to instal the services prior to switching over, ensuring the tenants minimal downtime.

The use of BIM technology allowed us to fully embrace the opportunities within the building by allowing us to work out ceiling and floor heights to maximise headroom prior to planning, and create verified views for the planning process. This technological approach allowed us to explore options for our client in a cost-efficient way, whilst reducing risk of planning refusal. It enabled us to take a holistic view of the building, ensuring fewer costly mistakes down the line. Our application was approved and the project moved forward.