Design: Wooden it be nice?

On a handmade shelf, in a former dairy cottage in the west of England, sits a slim tome called Briefing your Architect. It's a little bit dusty these days, however, as its owner Niall Hobhouse has got pretty good at briefing architects himself. In fact, the art dealer and property developer, who lives on a 1,000-acre estate in Somerset, has got so slick at it that his recent conversion of an old cottage into an architectural masterpiece – aided by Charlotte Skene Catling, better known in the architectural world for her Agent Provocateur shop fit-outs – won the Wood Award 2007 for a private house, and a RIBA award.

The dairy cottage used to comprise a wet room (now living room), the dairy (now kitchen), a cheese loft (now master bedroom) and other rooms inhabited by the cheesemaker and his family. Now remodelled, it has been extended to include a wide hallway downstairs and a bath house and plunge pool on the first floor. "It would always have been cheaper and simpler to build a modern house," says Hobhouse. "But I wanted to transform this old and not very distinguished building yet make it look, from the outside at least, that nothing very much had been done."

Outside the cottage was a washhouse, since condemned and pulled down. Hobhouse's brief to Skene Catling was to extend and modernise the building, making it comfortable without being post-modern or twee. "It's a sort of protest," he says. "Our nearby village of Yarlington is so very middle-class with white picket fences and absurd little pediments on the front of every house. So this house and the derelict farmyard opposite – they're both my protests against all that."

The house does look simple; although there are distinct "old" and "new" parts, the clean lines of the original cottage merge almost seamlessly with the modern extension, helped along by the use of the same Farrow and Ball paint colours and timber for the flooring throughout. The pièce de résistance of the project, the distinctive bath house, is made with alternate layers of oak timber and thick glass, supplied for this experiment by Pilkington. During the day, the striped walls allow an eerie half-light to filter into the bathrooms and at night the bath house glows from within. "It was really Charlotte's idea, that," says Hobhouse. "I showed her round the shed in the farmyard opposite where we stack some of the timber from the estate in an idiosyncratic pattern, with spaces in-between planks to let the air circulate and she took inspiration from that."

Skene Catling recalls she was "absolutely terrified" about this: "Timber moves an awful lot and I had nightmares about the whole structure twisting and the glass shattering."

The simplicity of both the structural design and the decoration of the interior could fool the casual observer into thinking that the house was a matter-of-fact affair to put together. In fact, it was quite the opposite."The idea was that it would look like it didn't take a lot of planning and work," says Hobhouse, "but it really did." The project took four years and cost approximately £700,000. "I sort of deliberately don't know exactly how much it cost," says Hobhouse.

The lack of original plumbing and the basic electricity supply complicated matters – especially considering the plans for a spa-like bathroom arrangement on the second floor, including a bath that used to be a cattle trough, rain showers and the outdoor plunge pool. "The whole idea with this place," says Hobhouse, "was not to make it look too grand, but this is a fantastically vulgar thing." Two bathrooms, which lead out into the pool, are filled with green light that reflects off the water, their ceilings patterned with ripples.

This is without doubt a house that comes alive in the summer – being a cheesemaker's cottage it was, after all, built to keep the milk and cheese at low temperatures. The downstairs rooms are kept cool by the thick stone walls and the bedrooms upstairs are set in the paths of breezeways. The master bedroom, furnished simply with a William IV four-poster bed and a 12-foot-high antique mirror, has a breathtakingly high ceiling. ("We took the original ceiling right off, which was a bit of a nightmare," explains Hobhouse.) It also has a wooden A-frame.

"This," says Hobhouse, "is probably the best bit of furniture we have. It's an 18th-century French architect's trestle. It's an exercise in over-structuring... I'm very interested in density and how you can cram as much as possible into one space without making it look or feel cluttered."

Indeed, in every bedroom, beds slide out of walls, ladders and tiny flights of stairs reveal more beds or lounging space, and an entire wall can slide across a gap to turn a little study and a room into a large bedroom. And if the structural ideas for the house weren't enough, all of the fixtures and fittings in the house are non-standard. "The fittings were all dismantled and silvered," says Hobhouse. "The doorhandles and the banisters were all cast in steel by a local steelworker. It's nuts really! The whole thing is just nuts. I'm slightly ashamed of it all now, in a way, but it is perfect, it's what I wanted and I do love it." woodawards.com