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Working Detail: Seafield House refurbishment by SLLB Architects

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[WORKING DETAIL AJ SPECIFICATION 10.09] Conversion of decommissioned nuclear bunker into modern villa

Seafield House, SLLB Architects’ refurbishment of a decommissioned civil defence bunker in the North London suburb of Mill Hill, raised three different types of challenge. On a practical level the architect needed planning permission to develop a building in the Green Belt, which was listed after the first submission was refused.

The existing fabric also presented a challenge. The external and internal construction was reinforced concrete, with walls up to 1.5m thick. The bunker, which was constructed in the 1950s, had fallen into disrepair. The proposed house would need insulation, weather protection and windows. Finally, there was the question of interpretation. The bunker, which was actually constructed above ground level, had become a monument to the Cold War era. How should the architectural expression respond?

Planning permission was finally awarded in 2004 after four submissions. This in itself was a triumph for the architect and the planning consultant. SLLB’s submissions were initially rejected on principal and later on grounds of detail. The planners objected to the proposed changes to the existing structure. In total, 12 planning and listed buildings applications have been necessary.

Subject to planning approval, the construction of the appendages to the building was relatively straightforward although work above roof level had to negotiate the large concrete ducts projecting from the building. Work to the existing fabric was more problematic. SLLB applied insulation to the external faces of the existing walls and roof to keep it warm, the large concrete overhang at the existing roof level had to be reconstructed and the existing walls
and roof had to be penetrated to provide windows for habitable rooms at ground level. The demolition work for each window opening lasted two days.

SLLB’s architectural expression was influenced by the fact that this was a commercial venture with the architect in the role of developer. Once the practice had decided to develop the bunker as a single residence, which would therefore be a large building, it needed to find ways to de-bunkerise the building. Practice director Daniel Smith emphasises the theme of contrast. A relatively lightweight construction, with floor-to-ceiling perimeter glazing, on the roof of the bunker accommodates most of the habitable rooms.

The accommodation on the lower floor includes the entrance area, a gym, secondary bedrooms and an entertainment room in the centre of the building, in place of the original map room (the bunker was intended to serve as a war room after a nuclear attack). As one ascends from the lower level through a central atrium, there is a dramatic increase in natural lighting levels. Luxury features are contrasted with the utilitarian austerity of the original building. These include air conditioning, a Vantage home-control system, a huge free-standing Kohler chomatherapy bath of decadent proportions, Grohe fittings and a vast kitchen. As Smith explains, kitchens in the current high-end residential market are on steroids.

There is also a sense of continuity with the original building. Many of its historic features, including massive doors with heavy steel plate ironmongery and a huge generator, have been retained and are displayed as reminders of the bunker’s intended use. SLLB did not express the overhanging upper roof as lightweight aluminium to maintain the gravitas of the original construction.

The architect deliberately chose to align the windows at ground-floor level with the inside faces of the walls to express their thickness and the granite surface effect where the original concrete has been penetrated has been left exposed. It specified external render on lathing, rather than a proprietary insulated
render system, which would not have felt like massive construction when it was tapped. Also, despite the opulent features, there is a sense of restraint, which recalls Wittgenstein’s house, for example, in the controlled colour palette and the retention of some of the original utilitarian light fittings.

The prevailing architectural quality recalls a Palladian villa on an estate in the Veneto. There is a piano nobile. The scale is generous, and there are rustic and utilitarian features, including a fountain, which has been constructed from concrete cylinders.

There is nothing precious about Seafield House. Design decisions were informed by pragmatic considerations. The first-floor terrace has an extensive sedum roof to save on maintenance. There is a green wall that, since a hardy species was required, has been planted with ivy. When I asked Smith why he called the development Seafield House, he replied: ‘you look and you see a field.’

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