Home Energy Efficiency

This page identifies ways to improve new house design to ensure a house uses the heat from the sun more effectively.   

All New Zealand houses are heated by the sun to some degree, but some are better at using the sun's heat than others. 

Designing your new house to include passive solar design principles will:

  • keep your home warmer in winter and cooler in summer;
  • help improve insulation;
  • reduce dampness and condensation;
  • save you money on power bills;
  • reduce air pollution locally.

Design Principles

There are three key principles to consider when designing your house to utilise the sun's energy:

  1. To encourage the sun's solar heat into the building.
  2. To store the sun's heat.
  3. To prevent the heat escaping out again.

Invite the Sun into Your House

Position your building so it is orientated to use the sun (eg have the main living areas facing the northern sun, place morning rooms such as the kitchen to the east, and have rooms needing less sun on the southern side).

Have larger windows on the northern sunny side to let the sun's heat into the house, smaller windows on the southern side to reduce heat losses.

Use shading to reduce overheating from the northern and western (afternoon sun) windows in summer, while still allowing the winter sun in.

Store the Sun's Heat in the Building

Once you have the sun streaming in through your northern facing windows, you need to store that heat. This requires using materials that create thermal mass.

Heavyweight materials such as concrete, terracotta and ceramic tiles, brick, mud or clay, all have inherent thermal mass. When exposed to direct sunlight during the day, these materials will slowly warm up and store the heat during the day, then slowly release that heat during the evening.

Thermal mass works best where the floors and walls receive direct sunlight (eg having a concrete slab floor, with tile finish, in north facing windowed rooms).

Thermal mass walls must be insulated on their outside surface, to stop the heat escaping. (the trick is to allow the sun to heat the wall inside the heat trap created by the insulation).

Carpet and textile flooring reduce the ability of the mass to absorb heat, so should be restricted to areas not being used for thermal heat storage.

The total area of northern windows needs to be balanced with the amount of mass available to absorb the heat. (eg. too much mass or too little solar admittance can make a house difficult to warm up).

Prevent the Heat Escaping

The sun is streaming in, warming your north-facing living room with its thermal walls and floors. Now you need to make sure that heat isn't lost back outside when the day cools.

You need to insulate all your exterior surfaces - under the floor, outside walls, roof and windows - to reduce heat loss.

The NZ Building code specifies only the minimum level of insulation required. More is usually better, resulting in a warmer more comfortable home and lower energy bills (eg. doubling the insulation will halve the building's lifetime energy costs. Instead of needing an expensive woodburner, all you may need are a few cheaper electric heaters).

Insulate your windows using double glazing or properly fitted heavy curtains. Double glazing will reduce heat loss through windows by nearly 50% in winter, as well as reducing noise and condensation.

Other Ideas to Consider

  • Most architects should be able to design for these basic passive thermal principles. Many can go a step further.
  • There are many 'environmentally friendly' construction materials and products on the market that you may wish to consider.
  • Alternative energy options, like solar panels, solar water heating, wind or hydro, can save on electricity bills.
  • Having a well designed, energy efficient house will mean you should NOT need to install a large heating system like a fire or woodburner, as small controlled appliances are probably all you will need.

Costs of Energy Efficiency

The cost of adding passive solar design into a home is highly variable, depending on the size of house, construction materials, site variables, and many other factors. The factors will affect the payback period. However, in general, over an average house life of 80 years, the additional cost will be saved many times over.

Passive solar design is easiest, and cheapest, to incorporate during new construction. However, some measures to increase thermal performance (such as increasing insulation) can be retrofitted to most buildings.

If only the economic cost of some thermal measures (eg double glazing) are compared to other traditional methods, the cost can be quite high. However, the potential energy savings and other benefits that may also result (eg. warmth, less condensation, noise reduction) should be included as part of the cost-effectiveness assessment.

Related Links

Listed below are some other references for energy conservation ideas.

  • The Energy Efficiency Conservation Authority of NZ publicly promotes and shares good energy efficiency ideas and research.
    EECA (www.eeca.org.nz)
  • The Building Research Association of NZ conducts independent research into improved building technology, including environmental and energy efficiency methods.
    BRANZ (www.branz.co.nz)
  • The Victoria University Centre for Building and Performance Research conducts building research.
    CBPR (www.victoria.ac.nz/cbpr/)