Ground force: The eco-house

When Luke Tozer was looking for a challenging site on which to build his family's new home, the architect certainly got what he was after. Not only has he bought and pulled down an 8ft-wide house squeezed into a passage between two villas dating from 1860, but he's replacing it with an eco-house. If that hasn't been testing enough, the west London project is in a conservation area with a highly organised and vocal residents' association.

"Most architects would like the opportunity to build their own house, and this happened to be site that came up when I was looking," says Luke, standing in a genteel street in Bayswater in front of what will be his four-storey home.

The original house had been built in the 1960s and came up for sale following the death of its elderly owner. It was in such a dilapidated state that it had to be pulled down and rebuilt. While its unusual shape put off developers, it attracted Luke. "Only an architect would buy that house and think '8ft wide - how exciting'," says the 36-year-old.

He put in a planning application a week after its purchase in 2005. "That was a battle because we discovered that the immediate neighbour on one side is the treasurer of the local residents' association. The lawyer of the owner of the house on the other side is the secretary of the local residents' association, and they all objected to our proposal. After some amendments, principally to the front elevation, and a lot of lobbying, we managed to get consent."

Very early on, he commissioned the environmental team of Arup, the engineering firm, to do a feasibility study on how the family could reduce the carbon footprint of the house and reduce carbon emissions on an ongoing basis. Of a number of suggestions, the most extreme they agreed upon was a ground-source heat pump, a system that exploits the constant temperature of the soil beneath the ground to provide underfloor heating and hot water.

Below the first metre of soil, the ground (in the UK at least) is pretty much - summer and winter - a constant 12C. In winter, a water and meths mix will be pumped through three 50m-long pipes that run into the ground. This mix comes out of the ground at 12C, runs through the heat pump which extracts and condenses the heat into the underfloor heating circuit, thereby cooling the mix to zero or minus 2C. It then goes back into the ground and comes out again at 12C and repeats in a cycle.

"It's a very similar process to what a fridge has, where you've got a cool inside circuit and a hot outside circuit," says Luke, co- director of Pitman Tozer Architects. "The amount of electricity that you use to drive the process is between a third and a quarter of the energy of a condensing gas boiler, so it's a very efficient. In terms of energy consumption, it should be much less than having a conventional boiler."

In summer, the process can be reversed. The heat in the underfloor heating within the building is extracted by the heat pump and pumped into the ground loop, where it cools. Hot water (for baths and showers) is provided by the heat pump in the same way as winter but only for an hour or two per day (at night using cheap electricity).

The whole installation, including drilling the holes, a heat pump and all of the plumbing, came to £18,000. Luke received a grant of £1,200 from the Energy Saving Trust, a non-profit organisation funded by the Government and the private sector to achieve the sustainable use of energy and to cut carbon dioxide emissions.

"The initial projection, and it'll be interesting to see when we live in it, is that we'll save around £500 a year in heating bills," says Luke who is married with a young son. "That said, the main reason we'll save is that we're spending a lot insulating the house, so the energy requirements are unusually low. That's the most cost-effective thing we've done, and anyone can do. Within the internal floors and walls we've used lambs' wool, and in the external walls and roofs we had to use more compact, high-density insulation."

It'll take around 24 years for the system to break even. But Luke's installation is far from typical. Ground-source heat pumps are more commonly used in houses with large grounds where the pipes can be buried horizontally. About £9,000 of Luke's budget went on drilling vertically, and that was partly because he could find only one company that had a narrow enough drilling rig to gain access to the back of the house.

The cost of installation for the average three-bedroom house, where the pipes can be buried horizontally, is around £10,000, about three times more than a conventional heating system. They are, however, expected to last about twice as long. Then, of course, there are the reduced bills.

Luke admits it's been an expensive option. "It's done principally for environmental, not economic, reasons," he says. "It's also good research and development for Pitman Tozer [his practice]. It's not something we've done before and most clients are wary about you experimenting on them, so I'm using myself as a guinea pig. Relative to the cost of buying a building in west London, knocking it down and building a whole new house, it's a drop in the ocean."

Ground-source heat pumps have been used in Sweden, the US and Canada for nearly 20 years. They're now a mass-market product and costs have plummeted. There are still only about 3,000 in Britain, which has historically relied on oil and gas, prices for which have been kept artificially low. Many of our buildings are also old and draughty, and therefore unsuitable for a heat pump - good insulation is vital. But developers are starting to use them in blocks of flats. Geothermal International, which supplied and fitted Luke's pump, has installed them in schools, hospitals, a church, office developments and large new residential homes with sufficient land.

Patrick Sherriff, the firm's marketing and sales director, says: "It's expensive but you're talking about reducing fuel bills by 70 per cent, and you're looking at a capital outlay that you will pay back within six to 10 years for a residential property. For a commercial property, it's two to four years. For commercial buildings, it's a no-brainer. For residential, it's a longer game, so you have to decide how long you're going to be in the property. It's not technology for everyone. If you had a draughty Victorian terrace with little room to put the groundworks in, it's not the right solution."

Back in Bayswater, once the 1960s house was demolished by hand, the three 50m bore holes were drilled, after first checking that the Tube line wasn't running underneath the house. The rig was at the house for two weeks and mud covered the street. "It had to be power-hosed off every evening to keep everyone happy," says Luke.

Then building started on the four-bedroom house, which is due to be completed in the summer. Rather than using the heat pump to cool the house in the summer, Luke will rely on an even more efficient method: natural ventilation. The stairs are being built in a stack effect within a central void. "We have four floors and it will draw air up and out of the roof light," he says. "The wood is sustainably sourced larch from a monastic community in Austria that plants and harvests the trees."

The family has also installed a rainwater harvesting tank and a system to recycle the rainwater from the roofs and use it to flush the toilets. The initial feasibility study also suggested putting in photovoltaics on the roof to convert sunlight into electricity. But Luke's plans to install them have been thwarted by the neighbours.

"We had to reduce the amount that we were allowed because of planning constraints after objections from the neighbours," he says. "At the moment, we don't have enough area to get to the critical one kilowatt needed. We need about 8 sq m and we don't have enough uninterrupted roof area that would make it feasible to put the photovoltaics on.

"While encouraging low-energy buildings is in-built in planning legislation, in practice the planners shy away from it in the face of objections on conservation and design matters from locals. With opposition, particularly if it's from a local residents' group that's well connected and well organised, the fact that it's an eco-house didn't help one iota in getting consent. What they cared about was how the front elevation would sit in relation to its neighbours."

Nevertheless, the architect has got most of what he wanted. And, after high levels of diplomacy all-round, everyone is still on speaking terms.

Ground-source heat: the basics

* A ground-source heat system is said to be the most energy-efficient and cost-effective renewable energy available on the market today.

* The heat pump is connected to a ground loop via pipes that draw on solar heat stored in the ground. The heat pump transfers low-grade heat from the ground and upgrades the thermal content by means of a compression process to a temperature suitable for domestic heating and hot water.

* Sizes available are 6kW, 8kW, 12kW and 17kW.

* A ground-source heat system is 400 per cent more efficient than a gas condensing boiler. For every 1kW of electricity used, you get 4kW of free thermal energy from the ground.

* Carbon emissions from buildings can be cut by up to 50 per cent.

* No planning consent is required.

(www.pitmantozer.com; www.geoheat.co.uk)

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