Promoting healthy houses

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An Arrowtown building scientist is scathing about deficiencies in New Zealand’s building code in terms of energy efficiency and healthy homes.

Denise Martin, who specialises in testing buildings for airtightness, is a member of a Queenstown collective promoting the New Zealand Green Building Council’s Homestar rating tool, which she consults for.

She says the building code is “the worst way you can legally build a house in NZ”.

“If you put it on a scale, a code-minimum building uses an average up-to-150 kilowatt hours a square metre in heating and cooling energy.

“A six-rated Homestar building is at about 50 kilowatt hours a square metre and a Passive house is 15 kilowatt hours a square metre.

“In order to get from code minimum, you have to think about airtightness, insulation, ventilation and moisture.”

She gives the example of houses she’s seen where “they didn’t even get to putting insulation in, and condensation was already dripping from the ceiling”.

Martin, who’s recently formed her own company, BEO Ltd, focusing on building science consulting and testing, says it’s harder to convert long-time builders.

“For the older builders, it’s a typical case of, ‘we’ve always done it this way, and it’s all the code requires’.”

She believes the Homestar six rating is where the building code should be pegged at – most new NZ homes achieve only a three-to-four rating.

Despite criticising the number of local “semi-performing” homes, Martin thinks Queenstown probably leads the way in NZ with greener, better-performing buildings.

“There’s a lot of wealthy people who have travelled all over the world and have experienced good housing who are just not satisfied with what the building code provides, and ask for better.

“So there’ve been many projects here that were way above what you would find everywhere else in the country.”

Martin’s worked on several certified Passive houses in NZ and also big projects like Camp Glenorchy, where she did blower-door testing on all its buildings for energy performance.

On energy, she says the term ‘zero-energy building’ is “quite misleading”.

“It means that you technically generate as much energy as you’re using, but it doesn’t say anything about the quality or performance of the building.”

She says there can be problems with people trying to increase their building insulation.

“You’re creating a bigger energy-driver from inside to outside. In layman’s terms, the more insulation you put into a wall, for example, the more air and moisture will try to push through that, which can create problems inside the wall construction with mould and decay.”

She’d like to see more high-density housing in Queenstown, partly because “we don’t have the infrastructure” for single family-home subdivisions, and higher density means less surface area exposed to the elements.

“And it’s more affordable.”

scoop@scene.co.nz