What is Passivhaus?
Passivhaus is a concept created in Germany. The very first building of its type was built in Darmstadt in 1991, and since then more than 30,000 buildings around the world have been designed and constructed to this standard. Passivhaus is recognised as the international standard for passive design techniques. Duncan delved into the specifics.
"It's relying on a very well-insulated thermal envelope and also achieving a high degree of air tightness within the building. In Passivhaus, you don't lose air from inside the building. The idea is if you can keep the air within the house, the sunlight and even the occupants can create warmth without relying on mechanical heating," he told us.
"There's a very stringent set of criteria that they use. Passivhaus homes don't necessarily need to face directly north for passive solar gain. It's a very good strategy if the house is on a site that faces south and cannot get much sunlight throughout the day. It's very good when you don't get that exposure."
Whereas passive solar can rely on natural ventilation, Passivhaus designs rely on a small mechanical fan to circulate the air – one distinct point of difference for those looking at building a green home.
So, which is better?
"In essence, both Passivhaus and passive solar design have similar aims: to reduce energy usage and achieve good health and comfort for the occupants. I wouldn't say that one is better than the other, both approaches work together very easily – in certain situations one is clearly more beneficial and but it depends on a number of factors," Duncan concludes.
"What has changed in the past 20 years is technology. Technology gives very clear meteorological information about specific environments; it has given us insulated concrete slabs, insulated glass window, increased levels of insulation for walls and ceilings, and the ability to achieve airtightness inside a home. All these factors have further advanced passive design strategies around the world."
Passivhaus is very new and is really still proving itself in New Zealand. We're still yet to understand whether Passivhaus is suited for the country's climate characteristics, as well as the budget requirements for Kiwi construction.
Ultimately, the choice between the two sustainable building methods is one that depends on many factors – not least of all location and budget. When it comes to making a truly energy-efficient home, however, there is no question: one should always rely on the experts.