If one couple (and their architect) get their way, a conventional street in Hampstead will get something truly stunning - art perhaps, but certainly not arts and crafts.
Demolish a mellowed-brick, Quality Street chocolate box of a house and put up in its place a prefab made of two carbon fibre shells. Sounds adventurous? Well that is what the planning authorities in Hampstead, north London's corner of wisteria-clad whimsy, are being asked to approve

When the young London couple who are trying to get this project off the ground found the site near the edge of Hampstead Heath, they bought it for the wild garden - for the toads that live in its mossy banks and the mushrooms harvested in the back yard, as much as for the three hundred- year-old oaks that were acorns when the Bishop of London hunted the woodlands. It lies in a conservation area - not difficult in Hampstead - and they wouldn't lop off a single branch.

At least the house itself isn't listed. Seventy years old, gabled with a pitched roof, it was showing its age. So they had no qualms about commissioning a new one. Not from just anyone, but from Ron Arad, best known for his extraordinary furniture. Asking the man who once wired the steel staircase of his Covent Garden shop to a Moog synthesiser so that every footfall created its own music is as bold as getting Alexander MacQueen to design for Givenchy. The couple had admired his wavy steel stairs and scalloped walls in the Tel Aviv opera house. For Hampstead, Arad came up with a fine-edged, fragile shell of a house moulded in honeycomb aluminium, the same as the floor in jumbo jets. Coated in carbon fibre, it will shimmer opalescent white on site. If it ever gets built.

If it doesn't, it will be for all the wrong reasons. Too much respect for an insignificant building, for one thing. It was designed in 1929 by Charles Quennell, whose obituaries praise him as a "master with pen and ink" but not bricks and mortar. The original house was already out of style when it was built in 1929. Arts and crafts had fallen from favour as modernists made an impact in concrete and steel on both sides of the Atlantic. Under pressure to cut costs, Quennell used concrete lintels instead of stone above the Critall steel windows which were his trademark. You could call the interiors cosy, but cramped is better.

Castle-sized doors with mawkish wooden pulls instead of handles aren't quite so Merrie Olde England within low floor to ceiling heights demanded by the council at the time. Brutal surgery in the 1970s took away the wall between the drawing room and what used to be called the morning room, which now sits at a lower level like an empty paddling pool in one corner. The original staircase was replaced with an MFI number. No sign of the fenders or balustrades, furniture or gates that Quennell successfully designed.

The house that Ron Arad and his clients want to put in its place would land in the woodlands as lightly as a space ship. When the architect talks about "the shell", he loosely cups his hands, slightly apart, with the right hand hovering just above the left to describe its two self-supporting roof shells. This house is very light and very strong. The honeycomb aluminium is also very thin, which makes it look fragile, like a porcelain piece by Lucy Rie. This is an illusion the architects have emphasised with an opalescent white finish outside and a terracotta skim inside. This is all the more remarkable because it encloses a five-bedroom house with a media room and garages. Arad blurs the boundaries between inside and out with a swimming pool that is half under the roof shelter and half outdoors on the adjacent terrace. Assembled on site in four sections, this radical design has broken the mould of traditional house building with external walls that support the roof, the way that children still draw houses. "The shell" owes more to a mollusc than a man.

With his welding gun and spray can, Ron Arad likes to experiment with materials, pushing them to their limits. Because the makers of cars and planes are always looking at new ways of making things, he is drawn to their processing plants: a fibreglass factory in Italy that builds Ferrari bodies moulds his tables, and an aeroplane and helicopter body factory in Worcester vacuum-moulded the prototype of his latest aluminium stacking chair. At this year's Milan furniture fair he stacked 70 of them in a tower in the city's equivalent of New Bond Street, the Via Monte Napoleone. The top chair, nine metres up in the air, was made by Arad from curved electronic circuitry board wired to the Internet to beam out messages. At the international furniture fairs he is a star, getting the crowds and the queues for his show, the bouncers and the push for his signature. But in Britain he welcomes the indifference which allows him to experiment freely and adventurously. His appointment as the new Professor of Furniture at the Royal College of Art is the first real acknowledgement of his genius in this country.

Let us hope that the reaction to this house will be the next one. His house for the 21st century is so original and, at the same time, so sensible in the way in which it puts the fun back into functional that it would be hard to make a song and a dance - let alone a campaign - about its predecessor. Naturally, there will be preservationists and conservationists brandishing petitions and protection orders. But they will have a hard time persuading the authorities because the building isn't listed. Conservation regulations governing unlisted buildings, while they differ with each council - in this case Haringey - are primarily designed to prove that the building makes a positive contribution to the architectural or historic interest of the area. As demolition is required, English Heritage will be asked by the council for their comments on the existing old building compared to the anticipated quality of the new buildings. While the changes to the interiors won't count, they will be asking how well it reflects, in age, style and materials, the other buildings in the conservation area. On this count, at least, Ron Arad will not failn