The powerful rise of passive homes

Passive housing is flavour of the month or perhaps decade in New Zealand eco sensitive building. Sarah Catherall talks to builders, architects and most importantly, those enjoying the benefits of living in a passive home.

By Sarah Catherall
Photography by David Straight

Featured in Capital #65
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In their Kāpiti home, Diane and Ian Christison can sense the fresh, filtered air circulating through the rooms, even when the doors and windows are closed. Their new Waikanae beach house is a passive home – the most healthy, comfortable type of building being built in New Zealand. In the debate about healthy homes, passive homes tick all the boxes, and the idea is gaining momentum among New Zealand architects and some builders: they’re ventilated with fresh air, are completely airtight, have maximum insulation, windows of a high standard, doors and glazing with no leaks, and a thermal fabric. A passive home ideally enjoys a temperature of about 20 to 25 degrees in summer and winter.

According to Elrond Burrell, a Wellington architect and passive home specialist, about 20 buildings in New Zealand are currently certified as passive buildings or passive homes. A passive house is different from one which is solar-powered or eco-friendly. “There is no such thing as passive house principles. You either meet the standard or not.”

For a number of years, the Christisons lived in a beachfront house on Waikanae beach. Says Ian: “We got sick of the sand, the salt and the wind.”

Their house was also expensive to heat, costing about $800 a month in power bills. When a block of land by the river came up for sale, they bought it and hired architect Guy Shaw, and their builder, Mike Craig, to design and build them a passive home.

Moving in a year ago, they hoped to get by without any heating, but installed wall heaters last winter to top up the temperature. Diane is battling cancer, so needs the house to be particularly warm. Today, it is about 21 degrees throughout. “I’ve spent winter in my shorts inside,” says Ian.

In their pantry, a small ventilation machine the size of a wall oven and using the energy of a 80 watt lightbulb pumps fresh air through vents opening into each room. Every three hours, the system takes moist, stale air from the kitchens, bathrooms and utility rooms and quietly circulates filtered, fresh air through bedrooms and living spaces so the air never gets stale.

Metal curtains attached to the external facade drop down over the triple glazed windows in summer to ensure the rooms don’t overheat.

They have halved their power bill. Says Ian: “It’s slightly more expensive to build a passive home, but we’ve worked hard all our lives and we wanted a home that was really comfortable.”

Their architect, Guy Shaw, says “in an ideal world, a passive home would have minimal windows and a compact design with a limited roof and surface area to retain heat.” He says designing the house challenged the rules. It faces north towards the sun, and is a complex, sprawling design with a lot of windows.

Guy, who is working on a number of other passive homes around New Zealand, says: “The health benefits are huge because you have this constant exchange of fresh air, and also low humidity. For people with health problems like asthma, this is huge. The whole idea of designing a new home is to create places of health and wellbeing.”

According to Elrond, New Zealand has 15 different climate zones, which designers have to consider when they’re designing a passive home. The building code has just three climate zones. Wellington is defined as warm temperate – the same as Taupo – which means it doesn’t get extreme cold or heat like Central Otago, for example. An Auckland passive home – Auckland is classified as “warm” – can get by with double-glazed windows, while triple-glazed windows can be needed in Wellington, depending on the home’s orientation.

However, a typical 200-square-metre passive house would use two kilowatts of energy per day to heat – about the same as a hairdryer, about a quarter of that used by a standard home. Some owners don’t even install heating.

“Designing a passive home for Wellington and the region is relatively straightforward. But the thing that can catch you out is that if your view is out to the west, if you are angling the house to that view, you can end up cooked in those rooms.”

One of the key things about a passive house is the insulation, and here it comes down to the climate zone the home is in. While 90mm of typical wall insulation may suffice for a compact, multi-storey apartment building in Auckland, the Christison’s house has 200mm of insulation in the walls, and 320mm in the ceiling.

According to their builder, Mike Craig, homes like this don’t lose heat. “The great thing is that once the house gets to a level of heat, that heat doesn’t escape,” he says.

Mike says New Zealand joinery isn’t airtight, although airtight windows and doors are now being made. “In a normal house, you have hot and cold temperature swings all the time. An old villa will have about 25 air changes every hour, while the Christison’s house has just 0.27,” he says.

Mike has four passive houses to build in Kāpiti next year. The owners of one house he has recently finished haven’t turned the wall heaters on yet, and are comfortable with the 19-degree constant temperature inside. It takes patience to build homes like these. “But I’m really passionate about it,” says Mike.

On Salmont Place in Kelburn, two contemporary townhouses by Parsonson Architects were designed using passive methods.

According to architect Craig Burt, the owners “had lived in an old draughty villa at the top of the cable car, so they came to us wanting something very different”.

Architect Nicolas Zilliox, also at Parsonson’s, is a trained passive house architect. He says the aim is to keep the house at 20 degrees celsius, in both winter and summer. At times, the house can get too hot, as the west-facing windows let in a lot of sun in the summer. Also the north-facing front of the house is about 50 per cent windows, which leak heat, like most homes.

The back of the kitchen, living and dining area has a long, heavily insulated wall to keep the heat in. A sunroom is like a suntrap out the front of the house, where the couple love spending time in winter. “It’s like the old conservatory model but it’s treated in a much smarter way,” says Craig.

A ventilation system the size of a small washing machine sits in the pantry, circulating fresh air through the house. “It’s warm, and the air is fresh, plus it’s also very quiet because you’ve got heavily insulated, thick walls and double glazing,” says Nico.

He is trying to encourage clients to consider a passive home, although it does add cost and so can be the first thing to go under cost pressure. “In our view, though, these homes are around for 75-plus years, so you want them to perform as well as they can.”

The townhouses – which won a local New Zealand Institute of Architecture award – may not get the tick as passive homes. However, the owners, who did not wish to be named, are so happy and comfortable that they no longer escape to their Mount Maunganui apartment over winter. They have sold it.


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