13 APRIL 05

In a famous episode of the Simpsons, Homer falls through the back of a hall cupboard, Narnia-like, into an undiscovered world beyond. As family and friends gather outside, Frink reveals the shocking truth of the land beyond the coat-racks. He draws two overlapping squares on the wall and then, to gasps from his audience, joins their respective corners. Homer has fallen out of cartoon flatland and into the third dimension!

I shan't claim that Homer is a hero of mine but I've had his cupboard in mind for some time. Because the ground works of Tree House took so long, I became overly focussed on the low horizons of our concrete slab and lost sight of the pregnant nothingness above it. Now that the walls are finally going up, the feeling of smallness and constraint engendered by the building's footprint has been transformed into wonder at the size and possibilities of three dimensional space.

All great buildings achieve their impact primarily through their manipulation of space and anticipation of the human experience within it, a subtle craft that can easily go wrong: compare the sculpted brilliance of the Pantheon to the compressed, deadening enormity of the Millennium Dome. The articulation of space is just as important in the domestic environment but as the price of a house is so strongly determined by the number of bedrooms it boasts, indoor spaces are routinely chopped up into as many little boxes as possible.

When we were designing Tree House it took time to think beyond the ways of living that our three-bedroom Victorian terrace had forced us into, but our reward will be interior spaces that are both exciting and ambiguous. The single large room at the top of Tree House, originally slated to be two bedrooms, will be a study, spare room, dance floor, yoga room and potting shed. If two bedrooms are required in the future, it will be easy to partition the space to create them.

The ecological importance of adaptable structures should not be underestimated. The more narrowly you define the interests of a building's users, the more likely it is that large quantities of resources, energy and patience will be expended over the life of the building in the endless struggle to reconfigure the space. In contrast, most traditional forms of shelter are strikingly adaptable. For example in Borneo, where I was born, the Iban of Sarawak are famous for their long-houses in which whole communities live together under one roof by sharing large communal spaces and using flexible partitions to create private rooms.

Although we are rushing to build millions of new homes for an increasing population and more one-person households, the population is expected to start falling after 2021. Add in the complexities of changing work patterns and who knows what we will want from all these new spaces in the future?

If you are thinking of extending, converting or otherwise remodelling your home, make your new spaces as adaptable as possible. 'Future-proofing' can simply mean putting in services even if you’re not sure you will need them. For example, we're running a water supply to the top of Tree House but we won’t be bringing it out of the wall until some damp hobby of the future requires it. Similarly, if you're rewiring, run some cables up to your roof for the day when solar photovoltaic panels come within your means.

Inauspiciously, the episode of the Simpsons described above was one of the 'Treehouse of Horror' Halloween specials. Having found himself in bulgy three dimensions, Homer faces disaster when he is sucked into a black hole. Thankfully, although our budget for Tree House is a little precarious, saying that we are being 'sucked into a black hole' can still be deemed a slight exaggeration.