Windows

The design and installation of windows has a considerable impact on the energy efficiency of a house.

On this page:

• Window types
• Window energy rating scheme (WERS)
• Take action
  • Plan your window size and placement

Window types

Windows can be responsible for up to 31% of heat loss in an un-insulated house.

Single-glazed windows are prone to condensation.

Double-glazed windows can:

• halve heat loss through a window
• cut down external noise
• reduce condensation.

Window energy rating scheme

The Window Energy Rating Scheme (WERS) helps consumers to compare the performance of windows to find the right window for your building project.

Take action

Plan your window size and placement

Use these design tips to make the most of windows:

1. Window size and placement (Fig. 1)

• The total window area of your home should not exceed a quarter (25%) of the total floor area. If your house does not get much sun, keep the total window area below 20% of the total floor area.
• Place opening windows and doors on opposite or adjacent walls of a room and the house, to encourage cross-ventilation.
• Consider half height windows in rooms facing south, east or west, particularly bedrooms and studies.

2. Double-glazed windows

• Use double glazing where other window coverings are impractical, such as skylights, or where you want to have a clear view of a feature outside.
• If you need to prioritise, install double glazing to the main heated areas and large windows, and use good curtains elsewhere.
• Look for double-glazed units with a 6mm to 20mm sealed air gap between the panes.

3. Skylights

• If you are installing roof windows or skylights, keep windows small, do not put them in living and bedroom areas, and double-glaze them if it is impractical to have blinds or shading.
• Skylights work best for bathrooms, toilets, laundries and hallways. When adding a skylight, install a transparent diffuser at ceiling level to separate the light shaft from the warm room air.

4. Specialty windows

• Windows near the ceiling (high wall windows, roof glazing, skylights) can make rooms very hot in summer, cold on winter nights and create uncomfortable draughts if not properly designed and installed.
• Specialty windows should be double-glazed as it may not be practical to cover them with a blind or curtain.

Also refer to information on the value of insulating your windows in the section on Your home> Insulation.

Fig. 1. Size and placement of windows

More information:

• Window energy rating system [NZ Window Association.]