BEETLEBANK, Earwig Green, does not sound the most attractive of addresses. But down a narrow, hedge-lined lane in the Weald of Kent, where half-timbered, tile-hung cottages and converted oast houses are the norm, is a stunning modern home of yellow brick, green oak, plate glass and slabs of crystalline schist rock... with a view down the upper Medway valley, with woods, fields grazed by cows, and the stately pile of Penshurst Place beyond.

“We are so lucky to live in this wonderful valley,” says the owner, John Morrison. John and his wife Helen, both 58, have just moved in after 18 months of building work overseen by their son, Robert, who acted as project manager.

It is not the first home on this site. The previous house was a wooden Red Cross first-aid hut, erected in the First World War, that had been added to over the years. “When the wind blew, there were so many holes in it that the building whistled,” says Robert, aged 31. “It was a pull-down job and start from scratch.” And what a scratch it was – 7m (23ft) deep, served by three trenches for geothermal heating that were 50m long and 1.8m deep.

“The earth below the frost line remains at a relatively constant temperature, which equates roughly to the average annual air temperature,” says Robert, who trained as an oceanographer. “Here that is 12C (53F). The trenches contain pipes in the form of loops that bring the water and antifreeze solution out and back to the house. A heat exchanger in the house heats the water for two storage tanks, one to service the underfloor heating pipes and one to provide hot water for the kitchen and bathrooms. Each night, Economy 7 electricity is used to heat the water to 60C or 65C, to prevent legionnaires’ disease, but by the time the showers are used in the day the hot water temperature will be around 40C, about right for a shower.”

Beetlebank is in an Area of Outstanding Natural Beauty, so planning procedures meant that it was two years before the diggers were on site, in March 2006. “To get the living area my parents wanted,” Robert says, “we had to go into the ground; there are an awful lot of unknowns when you do that.”

Beetlebank is a lightweight steel structure with living space half above ground, half below. A central atrium brings light into the section below ground, which has a utility room, bedroom, media room, and an indoor pool and sauna full of natural light, supplemented by 100 low-energy LED lights. The pool has an underwater speaker. A cine-system can project TV or films on the wall. At ground level the living room has floor-to-ceiling glass doors that open onto a west-facing patio. The east side is all glass with a view towards Penshurst. There is an open fireplace on the north wall. The kitchen is open plan. On the south side of the atrium is the master bedroom with more great views. Another bedroom overlooks a water feature in the patio, across which is a two-man office.

Throughout, the flooring is of natural stone – crystalline oyster schist containing natural colours of blue and muted reds, with sparkling patches of fool’s gold. The same stone is used for the adjoining patio areas. If you walk over this flooring in bare or stockinged feet, you can feel the warmth rising up.

Find out how to build your own green home at timesonline.co.uk/greenhouse

FACTFILE

Most homes require a heating load of 8kW to 12kW. Installation costs about £1,000 per kW. Recouping the investment takes about ten years.

Ground-source heating systems can cut costs by 35 to 75 per cent, carbon dioxide emissions by 40 to 60 per cent, compared with a traditional fossil system.

The geothermal heating system for Beetlebank was designed by EarthEnergy, 01326 310650, www.earthenergy.co.uk . Robert Morrison: 020-7738 1557.

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