First eHaus airtight test a success

Wanganui's first "PassivHaus" passed one of its first tests recently.
The eHaus in the Lithgow Drive subdivision on St John's Hill uses a German design technique to make it airtight, retaining heat within to save energy.
Its interior and exterior are currently being plastered with the kitchen and bathroom going in soon. When it is finished in February it will become a show home for two months.
Nobody has yet made serious inquiries about buying it for the asking price of $590,000, but there have been inquiries from people thinking of building something similar.
The airtightness of the eHaus had its first test two weeks ago when Jon Iliffe, technical manager at Eco Build Developments, used an imported German fan to create negative pressure inside.
Smoke was wafted around outside to see if it would be drawn in.
Mr Iliffe said the house performed well, and more testing would be done later.
The fan exerted about 60pa of pressure - an amount that would cause the total air volume in a typical draughty Kiwi villa to be replaced 20 to 25 times in an hour, or five to 10 times an hour for a new house.
For the new house at 5 Webster Pl to meet stringent PassivHaus standards when finished, the same amount of pressure will change the air less than once.
The idea of being airtight was to keep inside any heat generated, for example from cooking or laptops, and exclude heat from outside.
An airtight house can be stuffy and retain the moist air created by showering and cooking. In a PassivHaus a 40 to 100-watt ventilation system draws out stale and moist air and transfers its heat into the fresh air pulled in.
Making the house airtight wasn't difficult, said Mr Iliffe.
The walls were made of polystyrene blocks held together by steel reinforcing with concrete poured into the gaps. They are plastered on the outside and lined with gib on the inside, and are airtight, as is the concrete floor.
A long-lasting tape plugs any gaps, and an imported German membrane seals off larger cavities.
Water from the house's 300sq m roof will be captured in a 10,000-litre tank concealed underground and behind a retaining wall.
The rainwater will be used inside the house for everything except drinking.
When the level in the tank drops to less than one third it will be automatically topped up to the halfway point with mains water.
Mr Iliffe said the mains water would come into the house directly to the kitchen tap, and go from there to the rainwater tank.
He decided to use the roof to capture rainwater after listening to a Palmerston North professor talk about harvesting it at a Sustainable Whanganui meeting.
Using it for toilets, showers and washing had several advantages, said Mr Iliffe.
It had less lime than Wanganui mains water so would not wreck hot water cylinders and kettles, and would also lather better with soap and detergent.
Second, it would keep some water out of Wanganui's often-overloaded storm water system.
Third, it would save unnecessary water treatment.
"Every litre of water that comes into a house is treated to a high-grade drinking standard, but only five per cent of it is drunk."
The kitchen tap would have treated town water because some people thought rainwater wasn't nice to drink - though others thought it was better.