The idealist home exhibition

Building a home doesn't just give you creative freedom: it can save money and help the environment. Fiona Rattray visits two houses, on show this month, which prove the point

A builder leans over a picnic table in a quiet suburban street. Picking up a tool he starts to grind a sheet of metal, shattering the peace. A magnificent tail of sparks flies out from between his legs. It's certainly mesmerising, but it's not the most remarkable thing in sight. Behind him is a piece of architecture taking shape, and, in this case, even pyrotechnics can't compete.

A builder leans over a picnic table in a quiet suburban street. Picking up a tool he starts to grind a sheet of metal, shattering the peace. A magnificent tail of sparks flies out from between his legs. It's certainly mesmerising, but it's not the most remarkable thing in sight. Behind him is a piece of architecture taking shape, and, in this case, even pyrotechnics can't compete.

With its strong profile and terracotta tile cladding, the house in Mountfield Road, Ealing, is unashamedly modern: you can't fail to notice it. Designed by London-based architects Burd Haward Marston for their clients John Brooke and Carol Coombes, the sharp-looking structure with its tilted stainless steel roof and double-height glazed courtyard is nearing completion.

The walls are up, the plumbing's in and most of the windows are there, but there's still a way to go before the owners can move in. Since the owners are also the building contractors, however, that shouldn't be too much of a problem.

Anyway, there's another incentive for getting the work finished. For, at the end of this month, this house will be one of over 500 buildings open to the public as part of the eighth annual London Open House weekend. It will offer a rare opportunity for the public to take a look at what can be achieved when you stop mucking around with the insulting budgets of make-over TV and pay professionals to tackle serious issues of design, energy consumption and practical use.

Building a new house in a city as densely populated as London is difficult. For one thing there's limited land to spare and whatever scraps are available invariably get snapped up by property developers who have the necessary cash and experience and know the territory. For another, local planning officers are notoriously intransigent, preferring to back schemes which don't rock the boat in terms of the local surroundings - in other words, paving the way for ugly pastiche or carbon copying.

Brooke and Coombes, though, had a couple of natural advantages which helped make their plan viable. For one thing, until two years ago the site of their new home formed part of their back garden. From the top of the wooden ladder that leads to the upper floor (the staircase hasn't arrived yet), you can see over the back fence to the smart Victorian house where they used to live. They sold the house and half its garden, retaining the other half and demolishing the garages at the end to create a site large enough for a four-bedroom house with front and back gardens. Their other advantage was that the street itself is so full of diverse examples of housing - ranging from dinky period cottages to 1950s bungalows and 1990s estate-style - that the council would have had a hard time justifying any planning rejection on the grounds of insensitivity.

Brooke, 59, and Coombes, 53, are an energetic couple - they have the healthy tans and athletic physiques of people who have been working outdoors. They've no experience of building houses - Brooke is an ex-television producer, Coombes is an artist - but they'd had some involvement with work on other properties and they were looking for a new challenge. Their desire to build a house came partly from necessity - the old house was too big for them and their three teenage children - and partly from the fact that the opportunity was there in the shape of the site.

Carol was keen to choose a modern design. "I've always lived in old houses and I thought, we have to go down the modern route and try it," she says. John needed more persuading, but a visit to the London Eye finally swung it. "You look down on London and you realise that the things that are interesting are the things that are the best of their period," he says. "Carol doesn't want to paint pictures in the style of anyone else, and we didn't want to build a house that was a copy of anything else."

They rejected traditional Walter Segal-style self-build schemes, largely on the grounds of aesthetics, and then, despite the fact that it is every architect's dream to build a house, found it difficult to find someone who "wanted to do anything interesting". They interviewed around a dozen architects before appointing the young team of Catherine Burd, Buddy Haward and Lucy Marston, all of whom are in their early thirties. Their choice was a good one - the practice is small but well thought of and has proved flexible enough to deal with the unusual demand of having your client as contractor.

The architects have come up with some imaginative responses to the brief. First, they've made the most of a long, narrowish site by turning the house side-on to the street. Second, the profile is dramatic. "We cranked up the roof plane so that it appears to float as much as possible," says Haward. High windows under the roof underline this floating quality, while ensuring both light and privacy in the bedrooms.

Entrance to the house is gained from a glazed courtyard/room incorporating an external staircase. The southerly facing aspect means that the house will gain maximum heat from the sun in winter, while a series of interconnecting narrow ponds around the outside will keep the house cool in the summer. The main structure of the building sits on pile foundations, with a series of steel columns supporting the heavily insulated stud walls, faced with clip-on terracotta tiles.

Architects are fond of "dry" building methods like this - ie ones which don't require cement and mortar mixing on site and which allow them to experiment with materials and textures other than brick. But in this case, Haward explains, it was an especially useful method given its accuracy and the inexperience of the contractors. You could also argue that this method is more energy efficient - conserving both materials and labour.

At David Matzdorf's new house in Lower Holloway - another of this year's London Open Houses - energy efficiency was of paramount concern. Matzdorf, 46, calls his house an "urbane eco-house", and he was determined to distinguish it from the ad hoc, hippy-dippy structures favoured by the green lobby. He worked with architects Jon Broome and Tim Crosskey of Architype to come up with a building which would incorporate eco-efficient methods while providing an elegant contemporary living space.

The timber frame Matzdorf house, like the Brooke Coombes house in Ealing, was built on a site that formed from part of a neighbouring garden but had been neglected and squatted on by illegal garages. To obtain the site, located in a leafy residential street, Matzdorf had to endure a long and stressful process which included bidding against a property developer. When he had finally secured it, he had to win over both the local council and most of the neighbours before he could get his scheme built.

The resulting house sits at the back of a small plot with a wide garden to the front. In contrast to the narrow, deep footprints of most London houses, the Matzdorf house is wide, with the walls flush to the boundary line. The curved "green" roof - the soil of which provides excellent insulation and will eventually be planted - houses a 10-metre roof light. Inside there are other "green" touches: a Douglas Fir tree trunk holds up a mezzanine landing; like the wood used for the frame of the house, this is British-sourced as, according to ecological principles, energy is saved in terms of fuel that would have been used by importing wood from abroad.

The walls are painted with ecopaints, which are made from renewable pigment sources and are solvent-free. But this house doesn't wear its ecobadge on its sleeve. It's spacious and comfortable inside, subtle outside. It may not "match" the other houses in the street but it's a big improvement on the neglected space that it has replaced.

Building a new house is not easy. It takes determination, energy and a degree of bloody-mindedness. But, financially at least, it may be worth the effort. The four-bedroom Ealing house cost around £270,000 to build - the price of a two-bedroom period cottage in the same street. David Matzdorf spent £225,000 on his, including the land, and it's now worth more than £300,000. With the built-in energy-efficient solutions, both should be cheaper to run than older properties.

Do the sums. If it's a toss up between slogging it out in the existing London property market and creating an individual, architect-designed, eco-friendly home there can be no contest.

London Open House weekend, 23-24 September, tel: 0891 600 061; website: www.londonopenhouse.org