Light house.

A nineteenth-century fire station has been converted with imagination and architectural restraint into a civilised and practical dwelling, lyrically defined by surface and light.

Simon Conder's austere imagination has transformed two dingy upper floors of a west London fire station into an airy flat for a cook, Stephanie Simon, and songwriter Andrew Hale. As a type, the fire station must be a pretty rare addition to London's stock of redundant buildings being converted into recherche dwellings. This one used to house horse-drawn tenders on the ground floor and has a legally protected facade. The two upper floors (never intended as living quarters) were deep on plan with small windows, so consisted of oppressive low-ceilinged rooms. The centre was dark and the building was overshadowed by a neighbouring mews house.

Almost perversely it seems, the clients wanted a flat with space and scale and light. They wanted a kitchen at the heart of an open living room, a main bedroom with bathroom, two ancillary rooms, and proper storage for clothes and for a large collection of records and compact discs.

Conder stripped away divisions inside the building leaving two clear spaces and built a soaring flight of tapering stone steps from the front door on the street to the second floor. Lined on one side by an external wall, it is separated from accommodation at each stage - bedrooms and hall on the first floor; living room, and kitchen on the second - by the curve of a storage wall, bow-shaped on plan and made of birch plywood. On the second floor, the ceiling was removed leaving the timber joists exposed and adding an extra dimension to the space. Throughout, the walls are generally of self-coloured plaster, and floors of waxed oak boards. The stainless steel kitchen units were designed by the practice.

Views from the top of the building are dramatic and, to take advantage of them and to admit daylight, a glass and steel structure was let into the central section of the roof. Sparely designed, floored with wooden decking this elegant glass enclosure floods the second floor with light and is reached by the sandblasted glass steps of a steel staircase. The roof can be retracted in good weather to create a hidden terrace.

Downstairs, bedrooms and a bathroom lead off a small hall under a translucent glass panel set into the living room floor to diffuse daylight downwards. The large main bedroom is purely defined by the qualities of unadorned surface and materials. The bed-head is mounted on the extended stone plinth of the bathroom and divided from it by a translucent screen lit to bring out the soft jade milkiness of the glass (the lamination is unique to the practice).

If the austerity of the bed's base verges on the spartan, the bathroom's refinement suggests another sensibility. A cedar bath is set within translucent jade walls on pale stone flagged floor. Soap makes the wood slimy so you have to wash in the shower before getting into the bath; the wood becomes wonderfully scented when filled with warm water. The experience is sybaritic.