This, in its simplest form, is a house which requires no external energy source to heat the home to a comfortable level - so any heat would be provided by the sun, as well as the general domestic heat provided by background electricity (appliances, lights, cooker, etc) and by the people using the house.

The house would be so efficient that it would only require an external topup in very extreme cases. These are the criteria by which the Passive House Institute (an Austro-German institute) certifies its housing and in Ireland there is only one such passive house, designed by an architect in Wicklow.

But there is another, more exact definition of the passive house - it is a house that requires less than 35kW hours per sq m per year. This is the criterion by which many of the timberframe housing companies in Ireland have built their passive houses. The largest of these companies (indeed, the largest timber-frame company in Europe) is Kingspan Century Ltd - formerly Century Homes.

"The difficulty with following the institute's guidelines is that they have been designed around climates that have sustained periods of low temperatures, " said Gerry McCaughey, chief executive of Kingspan Century.

"But look at the temperatures that we have had here recently - it could be minus 10 in the morning but it could rise to 15 degrees by the afternoon. If we were to follow the European criteria, then our houses would not be able to respond to rising temperatures as quickly. Our timber-frame homes have been designed to suit the Irish climate."

In terms of passive housing, timberframe housing is for a number of reasons. Firstly, passive housing requires a high level of air tightness and timberframe homes are inherently tight (especially so with the next generation of Kingspan Century timber frame homes, called the Tek House).

But timber frame also allows for larger amounts of insulation to be included in the build without having recourse to a very bulky structure - for example, according to McCaughey, to achieve the equivalent levels of insulation with a masonry home, you would needs 300mm-400mm of insulation on the external walls, while timber frames allow for walls as thin as 200mm.

But there is another disadvantage to trying to create a passive home from traditional build. "In Ireland, at the moment, if you want to build a masonry passive house you will need to do everything yourself, from gathering information to hiring professional subcontractors, " said McCaughey. "But we offer a one-stopshop solution, with all the technical back-up and supervision needed to create a passive house."