Gianni Botsford’s Hampstead house complements Foster-designed extension

Could you describe Reciprocal House and explain your design objectives?

Reciprocal House sits hidden behind a pub in Hampstead. An existing Victorian coach house was extended in 1968 by Norman Foster for a well-known journalist, who entertained a lot. Our project replaces that original coach house with a new structure consisting of basement, ground, first and second floors, within the original volume and footprint, and connects this new structure to the Foster extension. Our aim was to create a reciprocal relationship with the power and simplicity of the extension but allow our project to have its own identity and architectural language.

What was the brief for the project?  

The brief required the Foster extension to be retained and refurbished but the client was open-minded about the rest of the project. He needed a house that was private and peaceful for his family, acting as an antidote to his busy life. The brief evolved during the design process to ensure that the result was carefully tailored to his needs, so Reciprocal House is highly bespoke with every activity and function informing the final design.

Were there any significant factors that influenced the design?

The planning context was highly sensitive, requiring a structure that nestled among the existing trees, was not visually larger than its predecessor, and related to the angled forms of both the coach house and the Foster extension. The latter has a powerful presence, exerting a strong influence on the solutions that were generated, and anchoring the project in time, history, materiality and ambition.

Could you explain the external treatment?  

Access to this backland site was difficult, so the basement was constructed in contiguous piled walls while the structure above uses exposed in-situ concrete, optimised for the thinnest build-ups possible to create lightness and delicacy. Much of the facade is clad in a series of sails positioned at different angles. These are made up of profiled perforated aluminium sheets, coloured bronze to sit within the context and framed by galvanised steel. The rest consists of anodised aluminium windows, doors and fascias.

How did you go about designing the interiors?

The Foster extension is formed from exposed concrete blocks, a profiled and painted steel ceiling, steel lattice beams, and large-scale aluminium glazing. This limited palette influenced the palette of exposed in-situ concrete used in Reciprocal House, as well as the profiled perforated aluminium walls, and the use of aluminium for the bespoke furniture, spiral stairs and bathrooms. The house is surprisingly open and flexible but each floor has a distinct character and a diversity of views, looking into courtyards and small gardens or over expansive borrowed views of the landscape. Rooms can be opened and closed with blinds, curtains and sliding walls depending on the time of day, the seasons or who is home.

What was your approach to sustainability? 

Our main focus has been on passive design, optimising the house for privacy, views and relationship to sunlight. The exposed thermal mass of the house is used throughout to temper the light and the temperature. In addition, the house is opened up using the staircase void, which rises from the basement to the second floor. Here a large skylight draws air upwards using the natural stack effect, helping to cool the interior in summer. Also, it is an all-electric house with an air-source heat pump, underfloor heating, high levels of insulation and water recycling.

What was the main challenge?  

The project took seven years from first discussions to handover, and it required patience and determination to follow the concept over such a long period. Throughout the pandemic, we worked collaboratively with the contractor and specialists to realise the shared aim of quality, detail and precision. This necessitated using extensive off-site manufacturing and mock-ups for the internal fit-out elements.

Could you tell us about your favourite part of the project?  

Reaching the top floor and looking out through the trees to the views beyond. It feels like a tree house, and you are in your own world.

Do you feel that there are lessons from this project that might be applied elsewhere?

Reciprocal House is an adaptive reuse project that balances retention and replacement, and provides a model for the densification of cities. It is ‘locally adapted’ to its context, much like a species of plant adapts and evolves to perform better in different environments. This approach, starting with the forensic analysis of the site, allows nature to lead the design process, creating living spaces that embrace light, views, fresh air and privacy.

Gianni Botsford is director and head of design at Gianni Botsford Architects

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Key data: 
Area 225m²