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29 September 2021

A total of more than 1,000m2 of Welsh Slate’s Penrhyn Heather Blues feature on the mansard roofs of four new storeys of luxury penthouse apartments priced between £17 million and £38 million at a former diplomatic building.

They were specified for the new-build element of the building’s ground-breaking redevelopment by Squire and Partners architects as they were a traditional material that was in keeping with the Conservation Area in Mayfair and their sustainability played a part in the BREEAM assessment.

Squire & Partners’ design establishes a new contemporary residential address befitting its Mayfair location. The building comprises 37 apartments and penthouses with resident amenities including a 25m swimming pool, spa, cinema, garden library, wine cellar and business suite.

The existing elevation has been refurbished and layouts amended to establish garden views from reception rooms and master bedrooms while the new, Welsh Slate-clad stepped mansards enhance the penthouse levels and improve the aspect across the surrounding Mayfair roofscape.

The Capital-grade Welsh slates were installed around 57 bespoke prefabricated dormer windows, recessed windows and sliding patio doors onto roof terraces by specialist sub-contractor Richardson Roofing who won a Pitched Roofing Award 2018, for a commercial property application using slate, for their work on it.

The fifth and sixth storeys featured 445m2 of 250mm x 300mm slates on a 75° pitch and the seventh and eighth storeys 639m2 of 500mm x 300mm slates at 60°, all fixed with counter battens and copper nails, with headlaps ranging from 60mm to 102mm.

Richardson Roofing’s commercial manager Conor Richardson said:

“Richardson’s were requested by the architect to make sure there was course alignment so we had to compensate for the varying pitches with varying slate sizes, all requiring non-standard gauges to conform to British codes of practice standards whilst giving the aesthetic appearance that the architect and client required.”

In addition to the existing elevation, the removal of an existing central bay, within two existing bookends, clarified the orientation of the building and established an identity with a contemporary setback elevation featuring a porte-cochère entrance.

Crafting traditional materials of brick, glass, stone and metal with modern technologies such as CNC machining, waterjet cutting and laser cutting has created an intricately detailed elevation drawn from the rich history of the area. Bespoke façade details include contemporary pilasters, fluted stone, projecting bay windows, linear balconies and ornate patterned metalwork.

From the sweeping entrance, a sequence of internal spaces connects to a garden library and courtyard to create a seamless transition from the local square. A double-height volume creates a dramatic entrance space and connects to the amenity levels below via a grand staircase with a feature lighting installation.

Richardson Roofing also carried out flat roofing, extensive stone paving and green walls to each terrace level, and the installation of a fall safe system.


Marcus White of Squire and Partners said:

“The Welsh Slate colouring was a good match for the surrounding traditional slate roofs. The planners received our design positively as it revived a historically significant building and the client was pleased with how the natural slate enhanced the interior interiors.”

The Pitched Roofing Awards judges said:

“These are luxurious penthouses with roofs that have been done in a luxurious way. The work is part-vertical and part-mansard which is difficult to do. This project identifies a high level of quality, despite being carried out in a difficult area, and was beautifully delivered.”

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