 Sometimes, you encounter a house that is not just special architecturally, but miraculous. Oak House, brought into existence by David and Jane Smith and a young practice called Baca architects is just that. Standing with the Smiths in their garden and gazing up at the curved segments of their new home, it seems inconceivable that such a radical design could have come to fruition on the edge of an area of Outstanding Natural Beauty in the Chilterns.  Oak House is described by Baca as a "bespoke five-bedroom luxury eco-home". But the market-speak obscures what has been achieved on the edge of a Buckinghamshire hamlet. Indeed, that phrase could have been cut-and-pasted from the estate agent's blurb that would have accompanied countless other designs by architects seeking to create a grand building in a secluded site.  Ultimately, the Smiths - David is an oboe and drum-playing London law firm director and Jane's a local music teacher who runs several choirs - rejected "tasteful" To The Manor Born-style historic architectural pastiche; and, in doing so, the couple are firmly on the side of the great 19th-century artist and historian John Ruskin, who reviled the spread of "Villa Frankensteins" in the shires and home counties. The Smiths wanted a home whose architecture revolved around the pursuit of music, yet would be thoughtfully innovative in form and environmental performance.  Seen in artistic terms, Baca's co-founder Robert Barker has given them an oak-clad, green-roofed sculpture, gracefully embedded in the hillside. Oak House has been designed with a striking combination of brave form-making and environmental innovation. It goes to show that award-winning eco-homes needn't be worthily clunky in form and hair-shirty in detail. Oak House, rather strangely perhaps, would not look out of place in the trendiest parts of, say, London, Sydney or Los angeles; nor would its design and construction cost, which came in just short of ?1m.  But think of the hundreds of ?1m-plus new-build homes out there that have made you think: "Good God, for that money they could have bought a really beautiful Georgian, Victorian or Edwardian home." Wealth does not, of course, guarantee the desire, or ability, to understand architectural qualities - or possibilities.  Eight years ago, the Smiths had the idea of selling their sizeable but architecturally unremarkable home, but keeping part of its large garden and building a new house that would suit their musical requirements, and those of their university-age (and equally musical) daughters, Tasha and Jessie. "I went on to Royal Institute of British architects search engine and put in something like 'eco-friendly architect' and Baca was at the top," recalls Jane. End of research. "They spent a lot of time finding out how our existing house worked. They even measured all the furniture. The big thing was that the music room was the centre of our old house, and our lives, and Robert picked up on that." Barker adds: "I've honestly lost track of whose ideas were whose." and he confirms that the Smiths were immersed in the design process from beginning to end.  "It was an absolute revelation when Baca came back with three outline proposals," says David. "One was open-plan, one conventional, and one pretty much as built. They had done sun-path modelling and had turned the house sideways on the site." Crucially, the final design reduced the width and height of the building: the Smith's pre-Baca attempt to get a house design through planning had failed because it was deemed too bulky. "Robert had also demanded that the planners be involved in the designs at an early stage." The result: they rapidly became intrigued by the design concept.  "We were very, very excited by what Baca proposed," says Jane of the year-long design and planning approval process. "We had loads of time to look at the drawings, and did a lot of tweaking. We would put in ideas, and were spending all our time just imagining what would work. as a family, we made a list of things we wanted - such as more space, en suite bathrooms for the girls. and with the music room at the centre of things." David describes the process as having been "a completely time-consuming hobby. and it became obvious to us that the position the planners were taking was much more supportive".  The architecture of Oak House is an outstanding demonstration of internal spatial organisation and environmental consideration. The house is entered from the top edge of the slope, with the living spaces on the upper level, and bedrooms and a big utility-boiler-washroom on the lower level. The south-facing fa?ade is segmented into three arcs whose angled and glazed facets look out into the Chilterns, rather than towards the house and garden that lie beyond a screen of trees along the lower, southern edge of the site. The upper level is immediately beguiling. The entrance leads straight into a bright, full-height clerestory spine that runs the length of the home's east-west axis. The first rooms you see are the dining room, beyond a glazed screen, and the capacious music room - piano, Clavinova and drum kit in evidence - under a gently barrel-vaulted ceiling. The music room has a sound-damped floor and ceiling, and can be fully isolated by 3.1m-high acoustic sliding-and-folding glass doors.  The east-west spine is a simple design move, but highly effective in the way it establishes, with great clarity, an armature for the living, sleeping and utility spa 