Passive design for energy efficiency

They chose double glazed joinery, with wooden trims on the inside to reduce heat loss through the aluminium. They also put a double layer of wool insulation in the roof cavity, and selected a log burner with eco-flue to reduce heat loss in the flue itself.

The house maintains its warmth well beyond their expectations. It is positioned to trap as much heat from the sun as possible, which helps heat the house during the day and means that on sunny days (even when the temperature only gets a few degrees above zero) they have no need for the fire.

Note: The basic principle of rammed earth construction is the ramming of moist earth into a movable formwork to form thick walls that can store heat energy. There are building firms who specialise in this type of construction, and you can find information about earth buildings on the Earth Building Association of New Zealand’s website: www.earthbuilding.org.nz.

• Parts of the house were benched into the land to help it blend into the coastal site and because the earth adds an extra layer of insulation, the inside temperature rarely drops below 15 degrees and summer overheating is limited.
• Thermal blocks were used below ground and on all exterior walls for added insulation.
• Pumice was used under the floor slab as insulation in lieu of polystyrene.
• Polyester wall and ceiling insulation was used instead of fibreglass, but next time the owners would use wool insulation for its breathing qualities.
• Solar water heating feeds to twin calorifiers (cylinders) designed to a European efficiency standard.
• Pre-wired for future solar power installation (when it becomes more affordable).
• A hydronic heating system fed from a condensing/modulating boiler and distributed over four levels through highly insulated multi-wall pipe to wall-hung radiators and underfloor in slabs.
• Deep eaves over windows to shelter from summer sun but which allow low winter sun to enter and heat. Some passive thermal walls where overall design allowed.
• A low particulate output (clean burning) wood-burning stove providing heat to the living, family, dining and kitchen area. It generates so little particulate after the initial start, that it is difficult to know if the fire is on from looking at the chimney.
• Rain water is collected from the roof and fed through river gravel and geotextile cloth covering the roof, down polyethylene (food grade) pipes into a 30,000 litre subterranean (which keeps it cool) water cistern. This supplies four toilets, laundry, two ponds and irrigation. It can also supply all drinking water (through extra filters and UV treatment) at the throw of a switch.