WHY PASSIVE HOUSES ARE VERY SMART

A passive house has key design principles that keep it comfortable and energy-efficient: •

uninterrupted insulation, including in floors, roofs, windows and doors; • a continuous flow of fresh air; • recovery of heat from stale air; • free heat from the sun, people and appliances.*

A passive house has an airtight thermal envelope, a thick ‘skin’ that wraps around it, keeping it warm. It consists of an airtightness layer on the inside of the insulation; the insulation layer; and a wind and weathertightness layer.

It keeps the indoor temperature around 20-25°C all year-round, a comfortable temperature for most people.

The bonus is passive homes tend to be very quiet.

A passive house course changed Warren Clarke’s life. The architectural designer runs his company Nook from the smart Christchurch home he built using passive house design principles.

“I knew and understood the value of good insulation, and good positioning of your house for the sun. But it wasn’t until we looked at passive houses and I did that course that I understood the value of airtightness, the envelope of a building and heat loss… that’s when I realised airtightness was as important as insulation. It was an eyeopener for me.”

To check a home’s airtightness, passive houses are ‘blow tested’ during building, and again when finished to check for air movements. An air movement is a draught coming in through a gap, which affects the home’s energy efficiency. To give you an idea: •

a house that is built to the New Zealand building code can have 6-7 air movements an hour; •

a house that was built in the 1950s-1970s can have 10-12 air movements an hour; •

a house that was built before the 1940s can have 19-20 air movements an hour.

Warren’s smart house scored just 1.77 air movements an hour.

“You go around with a little smoke wand, and where the draught happens, the smoke gets drawn to it. I found a small gap in my French doors and I taped it out for one of the blower tests.”

The test went from over 2.0 (air movements) before Warren taped up the draught, to under 2.0.

“That was due to a piece of tape that was only a couple of hundred millimetres long.”

The best houses score under 1.0 air movements. The passive house standard is 0.6, indicating a house built with incredible attention to detail.

“When you get it down to 0.6, it’s so detailed, it’s unbelievable to me,” says Warren. “It means the builder has spent a lot of time getting the building tape right.

Airtightness is as important as insulation when building a house.