Passive homes could be key to healthier future

With headlines hitting the news about damp, mouldy homes across the country, now is the perfect time to consider building a Passive House.

The concept of a Passive House (Passivhaus) originated in Germany in the 1990s, but they’ve only been built here in New Zealand since 2012.

Passive House Institute New Zealand board chair and architect, Elrond Burrell, is a certified Passive House designer and passionate advocate for comfortable, energy-efficient, environmentally-friendly homes.

He says building a Passive House requires careful planning from concept design, through detailed specification, to completion of the build. A certified Passive House has met strict performance standards relating to its building process, energy criteria, and airtightness.

Elrond first started researching the Passive House standard while abroad. “When I was working in England, undertaking very sustainable, green projects, we interviewed occupants and checked energy use. We found the buildings were not as comfortable or energy-efficient as they were meant to be. I found the Passive House concept to be a reliable solution for designing buildings that delivered what they were supposed to.”

Kiwi owners seeking the ultimate in comfort and energy efficiency are increasingly turning to the Passive House standard when building new homes. Elrond says it’s important that the design of a Passive House is adapted to fit an area’s climate profile. “A Passive House in Auckland is quite different from a Passive House in Queenstown, or even Wellington.” For example, triple-glazed windows are required in the South Island, but an Auckland home might only need good double-glazing.

NZCB builder Mike Craig, of Mike Craig Builders in Waikanae, has recently completed a Passive House for clients in Waikanae, just north of Wellington.

Because the house sits on a hill and gets hot sun in the afternoon, Mike knew meeting Passive House standards would require meticulous planning. “A Passive House must have fewer than 0.6 air changes per hour at 50 pascals of pressure. They do a blower test to check. It’s a measurement of air flow and a simple target that the Passive House Institute requires for new building Passive House certification,” explains Mike. “This house is 0.35, whereas an old villa might do 20 to 30 air changes per hour.”

These requirements ensure what’s known as the world’s most rigorous quality standards for energy-efficient buildings.  Elrond says a Passive House looks at how the whole building is performing, not just one part. “You have to do energy modelling, select the right insulation, windows and doors for the climate, and specify a highly efficient heat-recovery ventilation system.”

A building is only certified as a Passive House if it passes an airtightness test. Other critical elements to achieve the standard include a mechanical ventilation system and extra insulation. Thermal-bridge-free construction is also required, meaning areas where heat can escape or inundate a building are minimised or eliminated.

For the Waikanae Passive House, Mike’s team installed a mechanical ventilation system, extra-thick insulation, and triple-glazed windows. Mike says only five per cent of heat in the house is lost. “They have not turned on the heater once during the winter other than underfloor heating in the bathrooms,” he says.

A Passive House is free of condensation, mould, draughts, and maintains a comfortable year-round temperature.

NZCB builder Brent Chatterton, of Chatterton Builders in Canterbury, has also recently completed a Passive House build – in Rangiora. Structural insulated panels line the roof and walls, while inside, 265m2 of space beautifully accommodates all the other elements required for a certified Passive house, including thermal comfort and triple-glazed windows.

“The indoor temperature sits between 20 and 25 degrees and the indoor air quality is extremely high. Nobody fell sick in winter,” says Brent.

He says Passive construction costs 15-20 per cent more than a house built to minimum code standards, however, you can expect to recoup savings through much lower utility bills.

“When you look at the life cycle, running cost, and health benefits, these homes are definitely cheaper in the long run.”

Mike agrees – “The [Waikanae] house has all the health benefits – the air is filtered, which helps if you’re asthmatic or have allergies. It’s free of pollen and you can’t grow mould in a Passive House.”

Elrond says Passive House construction is on the rise in New Zealand. While just 33 projects were certified Passive near the end of 2020, another 80 Passive Houses are under way.

“When I returned from England in 2016, there were a few architects around the country doing Passive House design. In our firm, there are now five of us flat out with projects. We have gone from designing houses to designing community buildings, townhouses, and apartments. I think people are starting to realise we should expect more from our houses than we traditionally have.”

If any of these ideas have got you thinking about whether a Passive Home build might be right for you, we recommend you chat with a local NZCB builder. You can find your nearest NZCB builder here.

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