LONDON: Beware the snake-oil sellers. This is the advice traditionally handed down to any novice seeking to build their own eco-home. But compared with even the boldest of boasts offered by some within the green-build world, Tomas O’Leary makes an extraordinary claim on behalf of his family home.

“We hardly spend anything on heating and hot water each year,” says the Irish architect, opening the door to his five-bedroom home, which sits on a one-acre plot of land on the rural fringes of Wicklow, a town one hour south of Dublin that is fast being subsumed into the capital’s commuter belt.

“Last year, we spent just EUR240 heating our space and water and that includes our swimming pool. In comparison, a ‘normal’ house this size in this area would cost ten times that to heat.”

O’Leary has built Ireland’s first certified “passive house”, and he is justifiably proud. The passive idea was conceived 20 years ago in Germany by Dr Wolfgang Feist and it positively drips with common sense. The foundation of passive housing the standards of which are now overseen by the Passive House Institute in Darmstadt (passiv.de) is that the building needs to be airtight (sorry, no cat flaps). It’s equally important that the building has an expansive south-facing elevation that contains most of the windows (of course, that’s south facing in the northern hemisphere; in the southern hemisphere a passive house would have an expansive north-facing elevation). These two features together being airtight and loads of correctly facing windows give the best chance of using the sun’s free and abundant energy.

To prevent the home becoming as hot and humid as a rainforest inside, a network of ventilation ducts brings fresh, filtered air inside and expels stale, humid air outside. A heat-exchanging unit ensures this process uses only as much energy as a 60-watt lightbulb. First-floor balconies also provide “baseball cap-style shade” on hot days.

“Most of the houses built today are what I call ‘tea bag’ houses,” says O’Leary, as we stride into his home’s open-plan ground floor. “They leak heat everywhere windows, doors, walls and roof. A passive house aims to keep any leaks to a minimum. It’s not rocket science; there are no gizmos as such. The sun is providing all that free energy, so why not use as much of it as possible?”

The secret of a successful passive house, O’Leary says, is its windows. All of his are triple-glazed, with the cavities filled with argon gas to reduce heat transfer further. The timber frames metal frames are a no-no as they leach heat also contain thermal breaks made from an inch of cork. When I press my hand against the huge floor-to-ceiling window in the sitting room, I feel no coolness on the surface, even though the temperature outside is appropriate for a blustery, early spring afternoon.

“These windows are four times more efficient than normal double-glazed windows,” O’Leary says. “This is the future Germany has shown the way by recently banning the use of double-glazed windows because they’re not efficient enough. It shows you just how far behind the curve most houses built today still are. Builders have been getting away with murder with regard to the thermal efficiency of their buildings. The only way to address this is by really tightening up building regulations.”

O’Leary admits that passive houses require highly skilled joiners. His own monster windows must have cost a fortune. “They are expensive,” he says. “The cost of all the windows when we built the house three years ago was EUR50,000. The total building cost of this house was EUR420,000 euros so the windows were well over 10 per cent of the cost. But overall, especially when you consider how cheap they are to run once built, passive houses aren’t that much more expensive to build than equivalent-sized normal houses. The current thinking is that you can make this extra initial outlay back within seven years because of the reduced energy bills.”

But isn’t it unhealthy to live in an airtight house? “Quite the reverse, because all the air that enters the house through the ventilation equipment is filtered first. The machine is also expelling all the ‘bad’ air, too.” To prove his point, O’Leary opens the machine a fridge-sized cabinet and pulls out the filter that cleans the external air. It is thick with black soot which, he says, is produced by exhaust fumes from the nearby road. “When we stay in other people’s homes, the first thing we notice is how much cleaner our air is in comparison.”

The sitting room boasts a wood-pellet boiler, which O’Leary says is rarely needed for additional heating. For water heating, 71/2sq metres of solar panels on the south-facing roof provide 70 per cent of the home’s needs. The shortfall is met by a back boiler on the wood-pellet boiler.

It’s all so simple it makes you want to round up all the ministers currently talking so enthusiastically of building carbon neutral “eco-towns” and guide them round O’Leary’s home. Given that in the UK our homes collectively account for about a third of the country’s carbon emissions, passive housing’s achingly logical solutions need to be taken very seriously and soon. And who would have thought a five-bedroom monster with a heated swimming pool would have been the one to show the way? —Dawn/ The Guardian News Service