▲ Alder Hill Drive, Truckee, California, $2.75m
Where Just north of Lake Tahoe, about 300km and 3.5 hours’ drive from San Francisco. There are connecting flights from San Francisco to Reno (taking about an hour), which is 48km from the property.
What A 7,000 sq ft home with five bedrooms and five bathrooms. Built in 2000 to US “green standards”, the internal rooms include a dining room that seats 24, a home theatre and gym/studio.
Why The walls are made of rammed earth, 24 inches thick, using raw materials: earth, chalk, lime and gravel. A geothermal heat pump provides heating, passive solar and underground power. A high-tech mechanics room houses a well with a 3,000 gallon storage tank.
Who Chase International, www.chaseinternational.com, tel: +1 530 582 0722
► Hill House, Alresford, Hampshire, UK, £3.25m
Where In a small town in the south of England, around 23 miles from Southampton International Airport.
What A five-bedroom, five-bathroom house, built on the South Downs in 2008. With 6,394 sq ft of internal living space, the interior includes a cinema room and three reception rooms.
Why The current owner installed high-insulation windows, underfloor heating, and a Swedish ground source heat pump. In addition, there is a mechanical ventilation system with heat recovery, a wood burner in the centre of the house and photovoltaic panels.
Who Chesterton Humberts, www.chestertonhumberts.com, tel: +44 (0)20 7594 4746
► Cusignano, San Gimignano, Tuscany, Italy, €5.5m
Where 250km from Rome, 50km from Pisa International Airport and 60km from Florence Airport.
What A 13th-century tower with farmhouse attached. Set in 321 acres of pasture and woodland, the house has been newly restored with seven en suite bedrooms, a large kitchen, dining room and two sitting rooms.
Why High-quality insulation has been installed in the roof, windows and under the floors. Heating is provided by a battery of heat pumps that are powered by electricity, ensuring that the house emits zero carbon for all normal heating and cooling needs.
Who Cluttons Italy, www.cluttonsitaly.com, tel: +39 075 845 0100
► Country estate, Cham, Canton of Zug, Switzerland, SFr22m (£14.7m)
Where 38km from Zurich (40 minutes’ drive to the international airport), 1km from Cham village, on the lower reaches of the Lorze river.
What A restored estate with 4.52 acres of parkland. The estate consists of a 10-bedroom manor house with four kitchens, a mill house with a two-bedroom and three-bedroom apartment, a one-bedroom guest house and equestrian facilities with two staff apartments. Outbuildings include a bowling alley with games room.
Why A water turbine has been installed in a separate turbine house which, along with the geothermal heating plant, meets all the estate’s needs. The river water is also used in the fountains and gardens, and the geothermal heating plant with probes running 120 metres deep means that no fossil fuels are burned. The house produces no CO2 emissions.
Who Knight Frank International, www.knightfrank.com, tel: +44 (0)20 7629 8171
► Huf Haus, Idstein, Germany, €2.2m
Where Situated between Cologne and Frankfurt, in the Rheingau-Taunus-Kreis. Frankfurt International Airport is 30km away.
What A four-bedroom house, with a 116 sq metre apartment in the basement.
Why Huf Haus uses technology that separates the external and internal wall to minimise thermal bridging and maximise heat retention. All glass is triple glazed and designed to absorb passive solar heating, while the exterior wall is thickened with extra insulation, ensuring the whole property qualifies for the highest European energy standard of Code 6 for sustainable homes.
Who HUF Immobilien, www.huf-immobilien.com, tel: +49 2602 9979125