If you think an ordinary workman's Victorian cottage is narrow, Venus is narrower still: little more than the width of its neighbours' front rooms. It makes up for this, however, by filling its tiny site in all other directions - shooting upwards, backwards, even slightly downwards. Like a modern version of a jettied Elizabethan house, the first floor overhangs the street slightly, its strip of windows leaning forwards.

Technically, it's a "live-work" space. Because it was a semi-industrial site before, that usage continues. On the ground floor there is just room for a bathroom at the front next to the entrance lobby - which boasts the original big wooden door from the old sweatshop, salvaged and stripped - and the bottom of a tight grey-painted steel staircase, and then you step down into a slate-floored workroom. You could make clothes here if you wanted to, but today's version has more of a studio feel, good for designers or artists. A glass wall at the back opens out onto a tiny triangle of "garden" - in fact a minute yard, filled with flowerpots.

The first floor is the main event, as this is where the kitchen overlooks the street - sideways as well as forwards. With its big top-hung windows and curving white-painted timber ceiling, the kitchen feels very roomy, which it most certainly isn't. From here the oak floor runs back past a side window occupied by an artwork of coloured fluid-filled glass tubes (artist: Matt Hale). The living area at the back looks out over the neighbours' back gardens.

The final level - going right up into what in a normal house would be the attic - is a sleeping gallery overlooking the main space. It too has big window slots front and back, but the front one is set down low over the stairs. Every possible cubic centimetre of space is used.

And that's it. The materials used are very simple and hard-wearing. There's a fair bit of white paint, some bare brickwork, some use of industrial galvanised steel decking as upright partitions, a scattering of good furniture. And now its designers and owners have to decide what to do with it. "We were wondering," says de Silva, "if we couldn't let it out to Japanese Arsenal fans. They'd maybe come over for a couple of weeks at a time. Or perhaps we could rent it as a modern version of a Landmark Trust property."

That's about the size of it. Venus is a habitable modern folly in the 18th-century tradition, built as much for fun as for any practical purpose. It has wit and spirit - as you come in, you walk over a glass inspection hatch, again provided by artist Matt Hale, which reveals the house's drains in action. On the whole, the house works pretty well as a private art gallery - some light-box works by another artist, Frank Watson, look very good here. But all the practicalities are there too. So Chance and de Silva are considering moving in themselves for a while - they're conscious that people think architects should try out their houses - while renting out their real home down the street.

As for me, the Venus house almost makes we want to live in the country. That way, I could use it as the ultimate urban eyrie at weekends. Though maybe not on match days.