Paola Sassi: home is where the hearth isn't.

• Author: Pullen, Tim

You don't expect to find a contemporary, not to say minimalist, eco-house tucked into a quiet cul-de-sac of Victorian terraces in the Roath district of Cardiff. But that's only half the story because Paola Sassi has built her house, comprising two one-bedroom flats, to the German Passivhaus standard, which requires no central heating. In fact, no heating at all. On the mid-January day when I visited, the outside air temperature was just 7C, so it would not have been unreasonable to expect a chilly welcome. But the internal temperature was a comfortable 19C. And there was no heating--no central heating, no fireplace, no wood burning stove, nothing.

The Passivhaus standard was established by the Passivhaus Institute in Darmstadt, Germany in 1996. Since then about 6,000 houses have been built and certified to the standard across Europe and the US. What Passivhaus means, in broad terms, is that the building is insulated to a level that allows the sun and other passive heat gains to produce enough energy to heat the home. Passive gain is the heat from daily activity, given off by people cooking, using the shower, making toast and boiling the kettle. Pretty much everything we do produces heat that can be captured and circulated from warmer rooms (bath-room and kitchen) to cooler rooms (lounge and bedroom) by a heat recovery and ventilation system.

Sassi has gone to some trouble to ensure that the sun warms the house with big triple glazed windows to the south and solar panels on the roof. These produce most of the hot water for washing, showers, laundry, etc., and about half the electricity she needs. There are dual-flush toilets, flow-regulated showers and taps and a rainwater harvesting system which meets about half the water needs of the house. "I needed somewhere to live and could have bought a house cheaper," Sassi says. "But I wanted to prove that it is possible to build a house in a city center that is sustainable, comfortable and cheap to run."

Sassi, a professional architect, was born in Turin and educated in Munich. She worked for 15 years in London at two architectural practices before taking up a post at Cardiff University's School of Architecture. While working on large commercial projects, she became disenchanted with the levels of waste in the construction and use of the buildings. "It was our arrogant attitude that we can do whatever we want that struck me," says Sassi.

She decided that her house in Cardiff would be built entirely...