Finding building companies, designers, products and suppliers is one of the biggest problems people say they have when it comes to environmental design. Here are some key questions to ask.

Architects, designers, engineers

  • What professional association are you a member of? (e.g. NZ Institute of Architects, Architectural Designers NZ, Design Association NZ
  • How long have you been practising or interested in eco design?
  • What indemnity insurance do you have?
  • Can you refer me to examples of your work?
  • Can you refer me to clients you’ve done work for? Can I talk with them?
  • Does this seem like the kind of person I can work with? Do they listen?
  • Lists of practitioners are available on most association websites, as above, or at independent sites e.g.

Product suppliers

  • How long have you been in business?
  • Are you a member of a trade association?
  • What guarantee do you provide?
  • What is the measured performance of your product/system? How does that compare with similar products?
  • What are the maintenance requirements of your product/system?
  • What is the expected life of your product/system?
  • Can it be recycled?
  • Is your product/system appraised or endorsed by an independent, third-party agency, such as BRANZ, Envirochoice, Ecospecifier, FSC, Greenpeace, etc. (See weblinks.)

Building companies, tradespeople

  • What trade training, qualifications, and experience do you have?
  • Are you a member of a trade association (Master Builders, Certified Builders, Master Plumbers, etc)?
  • What guarantee do you provide?
  • Can you refer me to examples of your work?
  • Can you refer me to clients you’ve done work for?
  • Does this seem like the kind of person I can work with? Do they listen?
  • Do you have a rating on,, or a similar rating scheme?

also …

have a look at:


More information For further information, contact the council’s eco-design advisor on 0508 326 337 (0508 ECO DESIGN) – a source of free, independent, informed advice on creating homes that are healthier for you and the planet.

Ideal orientation of rooms for solar heating
Energy Efficiency and Conservation Authority, May 2000

This arrangement of rooms and windows around the different points of the compass is the optimum one, and when you have a big blank canvas, that is, plenty of flat, empty land, not especially difficult to accomplish. In compact, hilly urban settings, compromises and more complex arrangement of spaces will be necessary. The same goes if you are attempting to modify or extend an existing home. Nonetheless, it is worth the effort because your home will be warmer, lighter and altogether more pleasant to live in. And your power bills will be lower.

Thermal mass

So much for the ideal layout. The next concept to understand is thermal mass. Your design may be able to soak up every bit of winter sun, but without some way to store it, that heat will quickly dissipate. What you want is the slow release of stored heat over the course of the night. Enter thermal mass. This is the term for the ability of building materials to store the sun’s energy.

passive-solar-2Expose thermal mass to the sun
Energy Efficiency and Conservation Authority, May 2000

Four things determine thermal mass:

      • Type of material: The thickness and density of materials, chiefly walls and flooring, will largely
        determine how well your house can be warmed by the sun. (A thickness of between 100 millimetres and 250 millimetres is best. As for density, think weight. Concrete and stone, for example, soak up large amounts of heat. So, too, terracotta and concrete roof tiles compared with iron and decramastic roofing. For walls, bricks and concrete blocks are ideal. That stored heat lessens reliance on heating appliances. One Australian study found that a house with a concrete slab and insulated brick cavity walls had power bills 25 per cent lower than a timber-floored, brick veneer house of the same size.
      • Heat conductivity: A concrete slab in a northfacing room can absorb and store lots of heat, provided it is uncovered (that is, no carpet, though ceramic and slate tiles are fine) and has an insulation layer underneath. (As a point of interest, adding a brick or stone feature in a place that will
        get direct sunlight has the same effect, releasing
        stored heat as the interior temperature drops.)
      • Length of exposure to sun: A material with thermal mass needs between three and six hours’ exposure to the sun’s heat to work properly. Direct sunlight is twice as effective as diffuse light.
      • Colour: The colour of the material (the darker the better – think how white surfaces reflect light and are cool, while black surfaces absorb light rapidly and heat up).

Warmer weather

Understandably, you might imagine that a house with so much thermal mass would overheat in summer. But the sun is higher in summer than winter, so the summer sun’s rays do not penetrate as deeply or for as long into the house. Eaves and shading devices will provide extra protection. In addition, an architect will ensure window sizes are matched to the thermal mass of the house, further minimising the chances of overheating. However, materials with thermal mass work in your favour even in summer. That’s because they absorb heat in the air inside the home, providing a cooling effect during a hot day.

Passive ventilation measures are best worked in at the design stage. Examples are louvred windows, clerestorey windows and skylights (which add to solar gain as well as improving ventilation). Cross-ventilation is about the arrangement of doors and windows so as to allow the easy flow of air. Windows and doors should be located and open in the direction of the prevailing summer wind. This natural ventilation should ensure your need for fans and air-conditioning is minimal.


A last word about the design of your house: Consider the day-to-day needs of your family rather than building for the occasional visit of friends and relatives. And keep the design simple. A complicated layout will be more expensive to build and probably to heat, too.

More information
 For further information, contact an eco-design advisor– a source of free, independent advice on how to include
sustainable features in your building or renovation project

Other useful links:

  • Smarter Homes (
  • Sustainable building authority Level (
  • Energy Efficiency and Conservation Authority (
  • Building Research Association of New Zealand (
  • Department of Building and Housing (


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