It doesn’t need to cost more to build an energy efficient home, and you'll get better comfort and lower energy bills for years to come.
- Architects, designers and builders
- Site position
- Designed for the sun
- House size
- House shape
- Retaining heat
- Thermal mass
- Efficient hot water, lighting and appliances
- Case study - The Little Greenie
- More information
It’s important to work with architects, designers and builders who understand energy efficient design principles, know how the different components in a house work together and use computer modelling to understand a home’s energy performances before it is built. Not all architects, designers and builders are experienced with this, so it pays to shop around and get references.
The best building site for a warm, energy efficient home gets plenty of sun, particularly from the north, and is sheltered from prevailing winds. Bear in mind that the sun is lower in winter. You can easily find out how much sun a site gets at different times of the year using an app like Sun Seeker on your smart phone or tablet.
On clear winter days the sun sends around 500 Watts of heat through each square metre of unshaded north-facing window. A home designed to harness the sun's free warmth:
- Is placed on the sunniest part of the section – to access the most sun
- Is oriented to face the sun - with the main living areas to the north and service areas (for example garages and toilets) on the south side
- Has plenty of insulation - to trap in the free heat from the sun
- Uses thermal mass - like a concrete floor, exposed to the sun so it soaks up heat during the day and releases it when temperatures drop at night
- Has appropriately sized and positioned windows – moderately large on the north-facing side of the house, smaller on the east and west sides, and smallest on the south side
- Has properly designed overhangs over northerly windows to limit summer sun whilst allowing plenty of sun in during winter. Overhangs don’t work well on east and west sides as the sun is too low – deciduous trees and movable shades or louvers are better options here.
Think about how much space you need on a day-to-day basis. Smaller houses are cheaper to build, easier to heat and use a lot less energy.
The more complex a home's shape is, the more floor, wall and ceiling area it has to lose heat through. Simple house designs - for example compact rectangular shapes and multi-level homes - have less external surface area, so are easier and cheaper to keep warm.
Good design, materials and construction will enable your home to retain heat for your comfort and lower heating bills. The important factors are:
- High levels of insulation in ceiling, walls and underfloor, well in excess of minimum building code requirements
- Getting the insulation installed carefully without any gaps, tucks or folds to the New Zealand insulation standard NZS 4246
- Insulating any concrete floor on ground - both underneath and around the perimeter
- Insulating between any attached garage and the rest of the house
- Minimising plumbing and electrical services inside external wall cavities as they compromise the insulation and airtightness in affected cavities
- Double glazing with insulating frames and low-E glass
- Air locks at external entrances to keep out cold draughts
- Building airtightness combined with controllable ventilation provisions, like a heat recovery ventilation system.
Thermal mass is a term used to describe solid materials that absorb heat in daylight and release it when temperatures drop at night. If you build a house with windows that face north and rooms that get direct sunlight in winter, adding or exposing existing thermal mass will make better use of free heat from the sun.
- If you have an insulated concrete floor slab - consider exposing it (you can polish, paint or tile it) where it gets direct sun.
- If you have wooden floors - thermal mass can be added by pouring 50mm or more of concrete on top of the wood. Check with a builder to see if your floors are suitable for this option.
Ventilation helps remove moisture and maintain air quality. In summer, it’s the key to keeping your house cool and comfortable. The key things to know about ventilation are:
- Most houses can be well ventilated with adequately sized and located windows that can be opened
- Room layout and window placement can be designed to enable effective cross-ventilation, which is good for summer cooling
- In highly insulated and airtight homes a well-designed and installed heat recovery ventilation system can provide good ventilation and further reduce heat loss
- Properly sized and located extractor fans are essential for removing moisture from wet areas such as the kitchen, bathrooms and laundry.
Good design will cut your home's heating needs, but it still pays to make the heating system as energy efficient as possible. There are lots of log burners, pellet fires, and ENERGY STAR qualified heat pumps and flued gas heaters on the market, either as central heating systems or as individual heaters to heat areas of your house as required. Not all are created equal - for example, some heat pumps are twice as efficient as others - so it pays to do your homework.
The systems you use in your home can have a big impact on your home’s running costs and environmental impacts. Find out more about:
The 'Little Greenie' house in Golden Bay is a great example of energy efficient building techniques. It’s designed with 5 major principles in mind: energy efficiency, low maintenance and longevity, ease of construction and value for money.
- Good orientation and compact house design – oriented to get the best from the sun and to reduce heating loads.
- High levels of insulation, thermal mass and airtight joinery - retain heat from the sun. This ensures a constant temperature of between 18 and 24oC without additional heating.
- High efficiency double glazed windows and doors - provide controlled ventilation.