A simple guide to sustainable windows in MIXED CLIMATE zones

ZONES 4 & 5

Regions classified as mixed climate zones include Sydney, Perth and Adelaide.


Recommended window and door framing materials:

  • Aluminium
  • Aluminium, thermally broken
  • Timber
  • uPVC
  • Fibreglass
  • Composite


Recommended glass types:

  • Tinted
  • High Performance Tint
  • Tinted Low-E (low gain)
  • Tinted insulated glass unit (IGU)
  • Tinted IGU with Low-E (low gain)

About the SWA Project

The Australian Glass and Window Association (AGWA) are developing an industry-wide strategy to deliver more sustainable residential buildings through energy-efficient windows and doors. The SWA project has run over 4,000 simulations in all eight climate zones defined in the Building Code of Australia (BCA) using three house types with a wide range of windows to show the impact of high performance windows on the energy efficiency or star rating of the home. All results have been peer reviewed by a panel of Australian and international scientists.

About the Houses

The test houses were specified with R2.0 wall insulation plus reflective foil laminate (RFL) and R5.0 ceiling insulation. Although the insulation is in excess of the current NCC requirements, these insulation levels were implemented so that non-window heat transfer would be minimised, thus accentuating the sensitivity of the houses to window performance.

The results would not be credible if the houses were under-insulated to start with. Except where noted all houses had concrete slab-on-ground floors, brick veneer external walls and plasterboard internal partitions. It is well known that, for a given house, its annual energy performance for heating and cooling depends on its orientation. To account for this, each house was simulated four times with the house rotated progressively around the four cardinal directions. This yielded an average performance rating for the climate zone.

About Energy Efficiency

Choosing energy efficient windows will make your home more comfortable, dramatically reduce your energy costs and help to create a brighter, cleaner and healthier environment.

Windows are possibly the most complex and interesting elements in the fabric of our homes. They provide light and fresh air, and offer views that connect our interior living spaces with the great outdoors. However, windows can represent a major source of unwanted heat gain in summer and significant heat loss in winter. Windows can severely impact the heating and cooling loads of a building. Between 46% and 61% of a home’s heating energy can be lost and between 79% and 86% of its heat gained through windows. Improving their thermal performance increases comfort and reduces energy costs and Australia’s greenhouse gas emissions.

Selection Guide


Balance the benefits of solar heat gain in winter against keeping the cool in during summer. Use mid-range solar control. Reduce heat flowing through windows (in and out) over the course of the year.

Preferred U-Value


Preferred SHGCw

Mid-range (or ideally tuned by elevation)

Other Factors

Season-specific physical shading of windows (for example, eaves over northern-facing windows).
Windows with adequate openable area for ventilation.

Star Impact

SHGCw optimised (clear to tinted) - approximately 0 to 0.5 stars.
U-Value - approximately 0.33 stars for each unit reduction in U-value.
Ventilation - little impact beyond the average of 20% openable area.

Heating/Cooling Impact

Each star corresponds to reduction in Heating/Cooling requirements of approximately 20% to 30% on pre-improved level.
Star uplift due to reducing SHGCw reduces cooling load but may increase the heating load during cooler months.

Cost & GHG Savings

Approximately 3,000 MJ of energy saved per star, mostly cooling. Worth about $250 per year and up to 0.4 tonnes of greenhouse gases (GHG). Estimation based on a 240 m2 house located in Sydney, Perth or Adelaide.

NOTE: This information is provided as a guide only. For more detail, please consult your window or glass supplier, or visit the Window Energy Rating Scheme (WERS) website.


U- Value (Uw)

U-Value (Uw) measures how readily a window conducts heat. It is a measure of the rate of non-solar heat loss or gain through the window.

The rate of heat transfer is indicated in terms of the U-value of the entire assembly which includes the effect of the frame, glass, seals and any spacers.

The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value.

Solar Heat Gain Coefficient (SHGCw)

Solar Heat Gain Coefficient (SHGCw) measures how readily heat caused by sunlight flows through a window. The SHGCw is the fraction of incident solar radiation admitted through a window, both directly transmitted, and absorbed and subsequently released inward. SHGCw is expressed as a decimal between 0 and 1. The lower a window’s SHGCw, the less solar heat it transmits.

Visible Light Transmittance (VTw or VLTw)

Visible transmittance (VTw or VLTw) measures how much light comes in through a window. It is an optical property that indicates the amount of visible light transmitted.

VTw is expressed as a decimal between 0 and 1. The higher the number, the more light is transmitted.

This page can be downloaded as a PDF flyer.

A Simple Guide to Sustainable Windows - Mixed Climate Zones