RIBA Building of the Year: Barnstorming

Conservative attitudes almost put paid to a couple's dream home in north London. But Barnhouse is now a Riba building of the year

For some in Highgate Village, north London's very own post-Raj hill station, modern architecture is anathema, a tumour to be irradiated with disdain and rumour, something that must not be allowed to take root, in case it spreads. Fortunately, Philip and Carol Thomas were not about to accept such a diagnosis. They knew they had an extraordinary opportunity on their hands, and they were going to see it through.

The Thomases bought a small site, without planning permission, behind Highgate High Street – invisible from the road and partially screened by trees and shrubs from a handful of back gardens running away to the north-west on a shelf of land above the Highgate Bowl conservation area. The only thing on the site was a defunct grade-II barn, which housed stock for the local butcher's shop many years ago. A brownfield site, then; a scrap of useless land, all but forgotten.

But not by the Highgate Society. The unseemly brawl that ensued – that's how it felt to Barnhouse's progenitors, anyway – lasted for months and went to the wire. Haringey council's planning committee passed the design, by Charlie Sutherland of the Edinburgh-based Sutherland Hussey Architects, by a single vote.

Sutherland – who was responsible for the design of the British embassy in Berlin when he was with Stirling Wilford – remembers the Deputy Mayor of London, Nicky Gavron, voting against the development after telling the committee: "We're being seduced by good architecture."

It was, Sutherland admits, nerve-racking. "It seemed slightly political. There was a huge amount of opposition to the project. Maybe she [Gavron] didn't want to be seen to be going against the neighbours."

Gavron was, in any case, mistaken. Barnhouse is much more than good architecture: it's a brilliant essay in spatial manipulation and circulation on a highly constrained site that also feels good to move around in. Architects often say that fine buildings depend on good clients. Philip and Carol Thomas are familiar with the worlds of art and design, and they knew Sutherland had concocted something radical yet user-friendly as soon as he roughed out a sketch in the local Café Rouge.

"We had to find somebody who was going to be passionate and who understood that we didn't know what an RSJ was," says Carol Thomas. "It had to be somebody who wasn't going to lose their cool. We wanted somebody Gothic rather than classic, who could deal with all types of materials." The idea, according to Philip Thomas, was to "condense big ideas into a small space. The house had to represent the fact that it was in London, but part of the 21st century."

Sutherland's plans, using simple materials including rough-sawn oak beams and corrugated metal, envisaged a 400-square-metre house on the edge of a scarp; its longest wall would follow the line of the original barn wall. A large entrance and kitchen space turns right to form a central living- and dining-zone, then become a pavilion – a two-level wagon lit through which preserved trees grow. The whole form is bound together by a double-height conservatory that, in effect, bridges the two wings of Barnhouse.

But what is missing from this practical description is trajectory. Sutherland has, by using ramps, bridges and angles, created a dynamic building, a Tardis of sorts. There is no hint, when you stand outside the front door, that you are about to leave Highgate and its 4WDs far behind. Step inside, and it's game on.

The manipulation of space, and the scale and connection of the various rooms, carries with it a lucid sense of circulation. It's rather like Zaha Hadid's small but potent museum at Weil am Rhein, in Germany, in that the observer's smallest movement rewrites the spatial script entirely. Barnhouse is therefore a creative environment. The house reveals itself surprisingly, perhaps even a little mysteriously; it's lively.

Surprise and mystery do not interest everyone. When the Thomases' plans became officially available, they found that a posse of neighbours and the Highgate Society had taken against the scheme. The Thomases' response was to hold three open days on the site to explain what they wanted to build. Nobody came. But an English Heritage consultant pitched up and supported the prospective design.

Neighbours called in the ombudsman and insisted on an inquiry – "on the grounds that we had tricked the council", says Carol Thomas. "People used to tell us: 'Everyone hates you.'" But not Haringey's chief planning officer at the time, Paul Smith; nor the conservation officer, Eleni Makri. "He felt our scheme was a very good thing," says Philip Thomas. It was a blow against what Philip Thomas refers to – wearily rather than wrathfully – as the "repulsive snobbery that operates. It's the snobbery of fear. But there's a different clock ticking here. We are running at a different speed – and our clock doesn't go backward."

The Highgate Society, through its environmental section head, Michael Hammerson, denies that it was against Barnhouse on architectural grounds. "It's just that most of the modern things we've been saddled with have been awful. We do like to encourage good design. We, and the local authority, have kept off building on this backland. Our concern is that once one goes up, more will get built – more building, more massing."

The society also says that English Heritage "had no business commenting on it. It [the original barn] was a grade-II building. English Heritage's remit in London is to comment on grade-II* and grade-I buildings. We were very concerned about what was done with the site. It had been a slaughterhouse for a long, long time. In agricultural and historical terms, it had to be dealt with very sensitively."

In those terms, the Thomases – under a different chief planner or conservation officer – might have suffered. That a new Barnhouse does exist highlights the great difficulties faced by planners, clients and their architects mired in the thorny ground of backland or brownfield development. Anything truly different, even if it meets specific site constraints, will lead to a dogfight.

Highgate has a small architectural gem as a result, one good enough to win a Riba building of the year award a month ago. An architectural victory in a war that, on the greater scale, is being lost. For every Barnhouse, how many similar projects, driven by adventurous clients and more adventurous architects, die messy, acrimonious deaths?