When Forstater Productions bought 42A Devonshire Close in central London, it took on a ramshackle dwelling with no obvious circulation route….

Kay’s brief was to transform the multi-level building into comfortable offices for the film production company and a flat for its main producer when he is not away on location.

The two-storey mews house sits behind the Georgian buildings of Portland Place and was probably built in the early 19th century. Its ground floor is about 3m above the Portland Place gardens and it was built with conventional 2.5m floor heights.

A back extension some 50 years later provided two 4m high rooms which lined up with the roofline of the original property. This gave rise to an unwieldy 30s conversion where bedrooms, bathroom, kitchen and living room were all taller than their plans’ dimensions. The ground floor was taken up with a large garage and reception room with a tortuous stair linking the extension. The first floor was let as a separate flat.

Kay planned to rationalise the interior spaces, taking out the awkward changes of level caused by extension and conversion. Initial plans included breaking through beneath the building to found stairs which would extend the full height of the property. But site excavations revealed that the film company had bought more than it knew, as two vaults were discovered under a 220mm wall which supported the original mews cottage. This presented Kay with the simpler option of building down through the crown of the larger vault. Using the rest as a film store.

“The difficulty of the job,” says Kay, “is that it was not obvious what one could do from the existing drawings. It was only when the old staircase was ripped out and we started building from the other corner that we could see a way round the incredibly awkward spaces.”

The main entrance is through the mews into a light, airy reception which has been altered little. Unlike the rest of the house, which features a neutral gray carpet, the floor is made up of polished wooden blocks. This leads into the rear extension, with a new window overlooking the back courtyard, which is used as a secretarial office. Kay put in a new office floor to align it with the reception.

Kay has cut short the large garage to make room for cloakroom, toilet and the new stairwell. The stair doglegs back and forth across the original rear wall of the mews house, starting at its base, winding up through the crown of the larger vault into the back of the garage and turning back and up to the living room.

This complex system was needed to get under the mews first floor flat which was outside the site boundary. A spaghetti of pipe-work is hidden in a duct behind the back wall of the stair, with the left-over space formed into a keyhole recess at the upper landing.

The basement is taken up with three bedrooms, two of which double as offices for company staff. Kay has put in galleries to bring down the ceiling height of the extension rooms. The main bedroom leads into a single-storey bathroom in what, at one time, was the scullery. This room features Italian wall tiles with pink and purple diagonal stripes and ceramic floor tiles.

Two narrow windows onto the courtyard and two bow fronted beech pillars flank the basin. Kay has designed a second bathroom in the smaller vault, which is within easy reach of the other bedrooms.

The architect thought it prudent to avoid hanging fittings or pipework from the newly from the newly waterproofed vault surfaces. This constraint and the need for head-room above the shower and basin prompted a freestanding partition in hand-painted tiles by James Symcock. The result is a striking stepped ochre and red screen which avoids interrupting the flow of the vault surface above, and is complemented by more ceramic floor tiles and elegant bathroom fittings.

Returning via the new staircase to the first floor, the architect has removed a third of the intermediate floor, inserting two new floors to provide rooms or a size more in keeping with their purpose. The first formed the mews level office behind the reception and the second determines the long, light kitchen and dining area next to the living room. The living, dining and kitchen area double as the producer’s main offices. The living room is 4m high and leads up to the 2.5m kitchen.

This change of level meant the architect had to contrive an increase in the dining area by cantilevering the table seating above the living room. This extension and the kitchen joinery clambering down the stairs integrate the differing roles of the two areas.

The whole project was completed after 15 months for £85,000.