It's World Green Building Week. Kim Dungey takes a look at a Christchurch home so efficient, the electricity bills are predicted to be nothing.
The man behind the first 10-star home to be built in New Zealand hopes it will debunk the ''myth'' that building an energy-efficient house is too expensive.
Bob Burnett says the three-bedroom, two-storey Addington home has generated a ''huge'' amount of interest, with guided tours being held several times a week and a steady stream of drive-bys.
''The thing that spurs people's imagination is the fact you can have a house with no power bill. People love that idea.''
The property is the first completed home to be awarded 10-star certification by the NZ Green Building Council under the Homestar system, which rates the health, comfort and efficiency of homes.
Burnett says at least 90% of New Zealand houses carry only a three-star rating and that is mainly because people think they cannot afford more than the minimum required by the building code.
Other factors include a building industry that is reluctant to learn how to do things differently and a Government that does not want to improve the building code because it fears it will make building more expensive.
''It doesn't consider the fact that by building the cheapest possible houses, it could be harnessing the occupants to unnecessarily high power bills for the life of the buildings.''
Burnett says the conversation about affordable housing needs to focus on long-term savings and health benefits, not just on initial construction costs, and several tools are being developed to make this easier.
One is a dashboard-type graphic that will show what initiatives can be implemented, what they will add to building costs and what the running costs will be.
Another will show people the degree to which they can reduce their mortgage if energy bill savings are put towards additional repayments, while a third will show the extent to which a home's value is increased by green measures.
Studies from North America show energy-efficient homes are worth 10% to 20% more than standard ones, ''so if you put less than 10% into the building in terms of improvements, you're winning from the start without considering the fact that you might have much lower running costs and a comfortable, warmer, healthier home''.
If all New Zealanders lived in healthy homes, there would be 30% fewer hospital admissions for asthma and other respiratory disorders, he added.
''We've got real issues with cold, damp, mould-ridden homes and it's a serious problem because even new homes are not good in terms of those things. We're not learning from our mistakes and changing our ways.''
The Addington show home, which features PV solar panels and good thermal design, is one of two in Church Square that Burnett has designed to 10-star Homestar standards.
The Christchurch-based architectural designer is part of the superhome movement, an industry group that is encouraging the building of 1000 new homes rating between six and 10 stars.
He says building high-quality green houses should be standard practice in New Zealand and plans to have the Addington show homes open to the public for at least a year.
Many of the things in the 10-star home were not difficult to do but New Zealand was about 15 years behind Europe in the way it built, he said.
Building costs in New Zealand are among the world's highest but there is a lack of skilled people in the industry and the quality of building is ''very low''.
About 95% of New Zealand windows have aluminium frames but aluminium is a good conductor of the cold, so the ones in the demonstration home are PVC, as used in Europe and North America. Underfloor heating is fairly common here, but has not been done well, he says.
Most builders insulate under the floor slab only, forgetting about the footings and the edge of the foundation, where 80% of heat is lost.
And a recent report by the Building Research Agency of New Zealand found that more than 75% of insulation is not installed properly.
Despite there being a lot of talk about green, energy-efficient buildings, they account for less than 5% of building in New Zealand, so the superhome movement will be providing open-source sharing of information and industry training.
While the cost of the 140sq m home will be in the ''high 300s to 400,000'' dollars, few 10-star homes are likely to be built in New Zealand and a more realistic target would be six or seven stars.
A six-star home would halve power bills and add about 2.2% to building costs.
The Addington home uses a raft of innovative materials (see panel at right).
But Burnett says by far the most important thing is getting the design right, particularly in terms of the orientation and window proportions, and that is free.
Some people think passive solar design is simply a matter of having lots of north-facing windows, but too much glass will result in a home that is too hot in summer and too cold in winter.
Solar panels would not normally provide enough energy for heating, but the home needs less than half the usual requirements because of the energy-efficient thermal envelope, which includes better-quality windows, thicker walls, more roof insulation and a fully insulated floor slab.
''We're looking at the house as a machine with all these components working together, rather than thinking about individual components in isolation.''
Smaller homes are also more efficient to heat and use fewer resources to build in the first place.
While the rest of the world is ''trending downwards in terms of house size and thinking about quality'', New Zealand homes are still increasing in size and are now the second-largest in the world behind Canada.
Designed with no wasted space, the Addington home has a north-facing ground-floor living room with a centrally located staircase separating the entry, kitchen-dining and utility areas, including the toilet, laundry and walk-in pantry.
The landing on the staircase provides space for an office/computer desk and storage each side.
The master bedroom has extra storage and access to a small balcony.
Burnett says the aim is to create a tour of green homes around Christchurch and to produce a guide to creating a 10-star home that will be available as a booklet and online.
''It's not just about one house. It's about trying to create some behavioural change and really educate people.''
Key features
• Eighteen photovoltaic solar panels are tucked out of view on the roof.
• External walls are 140mm instead of the usual 90mm, which allows for more insulation.
• Frames are laminated veneer lumber - ''basically, a thicker version of plywood'' - which is the same cost as solid timber but stronger and more stable. The lumber is made from laminated log peelings so all of the tree is used and waste is minimised.
• Exterior framing is clad in a rigid air barrier (a board with taped joins), instead of building wrap, making the house more airtight and providing bracing that is at least double code requirements.
• Black aluminium cladding on the north-facing walls draws pre-warmed air into the cladding cavity and feeds it into an energy-recovery ventilation system. The system brings fresh air into the house and extracts stale, moist air, keeping the property dry.
• Slab-edge insulation stops heat loss from the concrete floor slab.
• Hydronic underfloor central heating, powered by the solar panels and using an air-to-water heat pump, is the most energy-saving feature in the home.
• Lighting is energy-efficient LED. Fittings are surface mounted because cutting holes in the ceiling for recessed lights would create breaks in the thermal envelope and allow heat to escape.
• Wastewater from the shower goes into a copper coil that takes the heat from it and transfers it into the supply water that goes up to the shower rose. Down the line, the water goes into a treatment system and, together with rainwater collected from the roof, is used to run the washing machine and the laundry tub and to flush the toilets.
• Windows are PVC frames with low E argon-filled glazing and tilt inwards so the house is ventilated but still secure when no-one is home.
• Taps are water-efficient models, all paints and sealants are low in volatile organic compounds and other materials are certified as eco-friendly.
See it
Bob Burnett's 10-star home, 11 Church Square, Addington
For more information, go to www.10star.co.nz or www.superhome.co.nz