Carbon-free NZ: in the home

...a typical three-bedroom house in the Auckland region built to Homestar 6 would cost only an additional 2.16% to build

Building on the foundation of the insulation and heating grants for New Zealand homes, we have much more to achieve in terms of energy efficiency.

You may not be aiming to build (or renovate) to ultimate eco-house standards, but understanding the causes of wasted energy and thus wasted money makes sense at every level.

Energy used in households matters because it accounts for about 12% of all NZ's energy demands. That's about twice as much as all non-industrial commercial use. So where does it all go? According to EECA in the average home energy bill water and space heating account for about 30% each, electronics 12%, refrigeration 11% lighting 6%, and cooking and the rest 11%. To make big savings it's most important to deal to space and water heating. Smart designers and architects understand this and design accordingly.

So, what are the most important things? First, it is about size, actually. We are second only to Australia in building the largest homes in the world. Don't mistake a low $ per square metre building cost as value for money. Ask yourself if you really need a bathroom the All Blacks could get changed in, or if you need four bedrooms, because you'll be paying the bills for heating them.

Second, insulate, insulate and then insulate some more. The building code only specifies a basic level. Going beyond this in ceilings, floors and walls does not cost much more as the labour input is about the same. 25% of heat is lost through windows, so double glazing is a good idea if it's a thermally broken system, i.e. the actual frames have an insulating layer in them. A key term to drop here is 'thermal envelope performance'.

Thirdly, think about heating. Funnily enough the best heat source is free and we call it the sun. If at all possible your main living area should have a north or north-west aspect. Good thermal mass design soaks up the free heat and releases it as the day cools. You may also want another heat source. Heat pumps are generally efficient but be careful about the specifications and actual performance in your region. One that's good for Whangarei may not be so hot in Arrowtown.

Also think about wood burners and pellet burners if local regulations permit. Now. Let's risk getting into hot water because at 30% of a typical bill water heating is a major unless you are able to install photovoltaic (PV) cells on the roof to provide the electricity. Relative costs and technology are changing all the time, so look around for options, particularly hot water heat pumps. Instant heaters remain a good bet, especially for smaller households.

New homes at Hobsonville Point in Auckland embody many of these design principles. The homes are a bit smaller than the Kiwi norm but that means less space to heat. They are very well insulated and rely mostly on heat pumps for heating. They have solar hot water or photovoltaic solar panels. Preliminary data from a study by Vector indicates that home by home, street by street, the energy efficient homes at Hobsonville have significantly lower than average energy bills. Most New Zealand new homes typically reach only Homestar three or four. Hobsonville Point homes are typically 6 Homestar and some builders are now producing 7 and 8 Homestar-rated houses.

People often perceive sustainable energy efficient homes as expensive, but they are becoming mainstream and affordable. Recent studies by Jasmax and eCubed showed a typical three-bedroom house in the Auckland region built to Homestar 6 would cost only an additional 2.16% to build and would be offset by a reduction in energy and water costs in about five years. Or if the house was about four square metres smaller there would be no increase in construction price.

Having sorted out the big stuff with heating and hot water, what about the remaining 40% of energy use? Well, here it can be fun because it is about shopping and using your smarts. Appliances that are Energy Star-rated by EECA are your friend. Downlights are not your friend, because they put holes in your insulation. Avoid them or specify those that can be covered by insulation. You'll want CFL or LED light bulbs because they use 80% less energy and can last for 20+ years.

Smart meters are here now. This technology is a platform for all kinds of energy efficiency goodies because sensitive measurement of use is the key to management of use. For example, Meridian has noticed that 25,000 homes in Christchurch seem to use more power at off-peak times. So just by switching to an off-peak pricing plan these homeowners will make substantial savings. This is good for New Zealand too - the more off-peak use we encourage the less peak time generation capacity we need to provide.

Oh, and put a timer on your towel rails. According to EECA that'll save the country $70 million dollars a year.

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Leigh Featherstone is the director of Homestar, the independent rating service that evaluates the environmental attributes of New Zealand's houses and apartments, both new and existing. Homestar assesses warmth, ventilation, water use, energy use, waste and site attributes, rating homes from 1 Homestar up to 10 Homestar. Visit homestar.org.nz for further information.