Cubic feat.

The conversion of a nineteenth-century warehouse into a modern apartment for a family of five preserves the integrity of the old structure and invigorates the spirit.

Shipping may have undergone a decline but there is still commerce in Antwerp's docklands though the city itself feels something of a backwater. Harbour docks are full of waiting barges and while some warehouses have been converted into dwellings others continue to be used for storing goods. Development of empty sites and buildings is taking place slowly. A plan for offices on an empty harbour site, drawn up for the port authorities by Richard Meier at the end of the '80s, was eventually realized in an atmosphere of controversy by a local practice.

About 100m away from the Meier site is the Marnix warehouse, a handsome nineteenth-century brick building overlooking a large harbour. Two years ago it was restored and divided into three large shells. More recently the uppermost one on two floors has been converted into a family apartment by Diederik Fokkema, who coincidentally had worked for Meier in New York not long after leaving university and before setting up his own practice in The Hague.

His client, Hans Lensvelt, is a Dutch furniture manufacturer, who had originally thought of creating a convivial guesthouse for visitors to the Lensvelt factory just over the Dutch border at Breda (p68). But the exceptional qualities of the warehouse structure, with its massive oak timbers and lofty volumes, impressed upon architect and client the conviction that they should impinge upon the building as lightly as possible. The scheme for a six-bedroomed guesthouse became one for an apartment for Lensvelt and his family.

Adaptations of industrial buildings, which tend to yield large amorphous spaces, into habitable dwellings have spawned an inventive vocabulary of light conductors, mezzanines, bridges, stairs and self-contained capsules. Fokkema's almost playful volumetric juggling develops this vocabulary further.

In plan the building is an irregular rectangle measuring about 8 x 21 m and, in its original state, weakly illuminated by warehouse windows at each end. Down the middle of each level marches a row of oak columns supporting floors of oak beams and pine planks. Lensvelt's shell included an attic floor under the the rafters and beams of the sloping roof, and a roof terrace.

From the first, Fokkema's idea was to create an environment in which this particularly lively family could flourish. Essential functions take place in self-contained capsules - three small cubes with white-plastered and sandblasted glass walls - to leave as much open space as possible, vertically as well as horizontally. Generally speaking, the lower floor is reserved for sleeping, washing and space for children's play; the upper one contains the kitchen and dining room and access to the roof terrace.

Luminance is brought into the centre of the plan by making skylights on each side from glass panels inserted between rafters, and by creating a central double-height void underneath that acts as a luminous conduit. It is spanned at attic level by a narrow bridge linking the kitchen at the rear with the living room looking over the old harbours. From the lower floor you can see clear up to the roof timbers and sky.

As if to assert their independence all the cubes are at different levels. Two of them rise from the lower floor through the void, the third is suspended from the roof. The first, encountered on entering, is enclosed front and back by a wall of sandblasted glass and contains a bedroom. An inner section (furthest away from the entrance) has been jacked up to form part of the kitchen wall above and an elevated sleeping platform at the bottom. Capped with a translucent glass panel, this chimney helps diffuse light into the room. Across the void the interior of the second cube, which floats above the level of the floor, provides two bathrooms, while its roof becomes a landing for the most minimal of stairs to the third, a crow's-nest bedroom, and to the roof terrace.

Fokkema's fastidious expression of old and new preserves the integrity of each. Though the cubes are abstract insertions they are made to emphasize the old structure. At times they wrap round it so that from outside you see a ghostly column through the glass; at other times they become a backdrop for details. Other new elements have been rendered equally abstract. Stairs to the crow's-nest, of wooden risers and treads only 60mm thick, are carefully connected without a supporting beam. Made in the Lensvelt factory their simplicity is a technical achievement. In the living room, under the narrow strip of windows on to the harbour, a low cill runs the width of the building. In the middle of it is simply a place for a fire, rather than a fireplace.

Only gradually do you become aware of such details because the combination of light and structure overwhelms. Fokkema's athletic grasp of space works horizontally as well as vertically. From the front door you can see down the length of the space to the translucent glass wall that screens the two luminous bedrooms at the end; it glows with light, making you aware there is something beyond. From the elegantly appointed kitchen under the skylights you can see across to the other end of the building and through the windows to the harbour buildings outside.

Architect Fokkema Architecten

Project architects Diederik Fokkema, Hanneke Veldhuis

Colour scheme and paintings Jacqueline van den Hour

Photographs Christian Richters