WHY PAS­SIVE HOUSES ARE VERY SMART

NZ Lifestyle Block - - SMART SERIES -

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.

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