The Gap House, a narrow new-build terraced London townhouse, designed by Pitman Tozer won the RIBA Manser Medal in 2009, the annual prize for the best one-off house or housing designed by an architect in the United Kingdom.

The house, which is sited on a plot only 2.3m wide within a conservation area in West London, proves that sustainable architecture is achievable without compromise on the tightest of urban sites. The house incorporates a number of green strategies including passive solar gain, high levels of insulation, a ground coupled heat pump and rainwater harvesting to minimize its carbon footprint.

It achieves all of this without compromising design.

Michael Manser, founder of the Manser Medal said:

‘The design is one of impeccable detailing and simplicity in every respect. The narrow front elevation is an acme of understatement and although frankly modern, at a first glance makes almost no impact. Just a narrow column of identical half shuttered casement windows, above a basement-level entrance door, all in a background of white stucco to match the adjoining houses.’

With a street frontage of only 8 ft/2.3 m wide the house sits within a narrow slot, originally the side alley and rear garden of an adjoining property.  The challenge was how to create a Low Carbon Building and make a comfortable 4-bed family home, maximising light and space within the constraints of a tight and awkward site.

The key to achieving a solution where each habitable room has good daylight and feels spacious, even within the narrowest part, was to stack the smaller bedrooms at the front of the house facing the street and to organise the rear in a cascading configuration with the wet rooms and storage occupying the parts of the plan with no natural light.  A courtyard at the rear of the site brings light into the ground floor reception space. A central twisting timber stair held as a piece of sculpture off the walls brings daylight deep into the centre of the plan on each floor.

The house was designed and built for partner of the practice Luke Tozer and his family and developed by the practice as a case study project allowing the partners to put in to practice new strategies for Carbon reduction and energy generation.

The house is designed to use approximately 30% of the energy of a typical house built to current Building Regulations, with a predicted reduction in heating bills of approx. £500-£800/annum. A recent in house post completion assessment rated the house under the Code for Sustainable Homes as grade 4 (Exemplary). 

This has been achieved through the following strategies:

1. High levels of insulation in the walls and roof (U value 0.15 W/m2K) and passive solar gain minimise heating requirements.
2. 3 bore holes measuring 50 m deep were installed below the rear courtyard serving a 12KW ground coupled heat pump installed in the plant room, which provides all the heating (including under floor heating) and hot water for the house. 
3. Water consumption is minimised through a rainwater harvesting system designed specifically to suit the constrained nature of the site, which is reused to flush the toilets.
4. Natural materials are utilised where possible including lambs wool insulation used for all the internal walls and floor and a sustainably sourced composite Larch board for the stair structure.
5. High performance low energy windows were specified with timber frames made from sustainable Spruce and the glazed units masking the external timber frames.  
6. As well as bringing light into the property the geometrically complex self-supporting stair acts as a four-storey stack for passive ventilation in the summer.

Sited in a conservation area between two listed buildings adjoining neighbours were prominent members of the local amenity society who raised vociferous objections to the proposals to construct a contemporary building in such an historic context. Lobbying of local Councillors and careful negotiation on the part of Pitman Tozer was necessary to convince the planning committee that a sympathetic, high quality modern building was appropriate. 

The completion of the house is a testament to the architects’ unwavering commitment to the integrity of the scheme and a belief in pioneering environmental design.

‘Overall the most impressive aspect of the design is its level of skill, imagination and practicality in creating a series of apparently generous spaces, despite all the constraints of overlooking, conservation policies and initially hostile residents association…The result is a comfortable home in a great piece of architecture.’
Manser Medal Jury