Timber or uPVC window — double glazed with                                              3.0                             0.61                 
3mm clear glass/6mm air gap/3mm clear glass

Aluminium window — double glazed with                                                       4.2                             0.69                       
3mm clear glass/6mm air gap/3mm clear glass

Timber or uPVC window — single glazed with 3mm clear glass                    5.5                              0.69                     

Aluminium window — single glazed with 3mm clear glass                             6.9                              0.77                        

​Uw                   SHGCw       

​   ​Total window system values

Indicative window types

Energy performance of common window types

Glazing is a significant investment in the quality of your home.
Walls of glazing create light-filled living areas.

The cost of windows and the cost of heating and cooling your home are closely related. An initial investment in energy efficient windows can greatly reduce your annual heating and cooling bill. Energy efficient windows also reduce the peak heating and cooling load, which can reduce the size of an air conditioning system by 30%, leading to further cost savings.

The Australian Window Association has developed a tool (see www.efficientglazing.net) that calculates the savings that may be achieved by energy efficient glazing. This tool compares window selections to a base aluminium window with 3mm clear glass.

​Life cycle costing

​Fading

Exposure to sunlight causes many modern interior furnishings to fade. The wavelengths most responsible for fading are the ultraviolet, violet and blue wavelengths. Appropriate glazing blocks some of these wavelengths and reduces fading, but does not prevent it completely.

Condensation

Condensation occurs when moist air is cooled or when it meets cooler objects. The interior and exterior surfaces of energy efficient glazing are closer to the adjacent air temperature, reducing condensation and the build-up of unsightly and unhealthy mould and fungus. Less efficient windows create greater differences between room temperature and glass surface temperature, facilitating the formation of condensation.

Thermal mass

Thermal mass does not create heat — it just stores it. For thermal mass to provide beneficial evening heat in cool climates it is essential that glazing is used to admit solar radiation during the day to warm the mass. (see Passive solar heating; Passive cooling; Thermal mass)

If thermal mass is used in warm and hot climates to absorb heat from the air, minimise solar gain through glazing and do not locate the mass where it is exposed to solar heat gain.

​​Thermal mass

Thermal mass does not create heat — it just stores it. For thermal mass to provide beneficial evening heat in cool climates it is essential that glazing is used to admit solar radiation during the day to warm the mass. (see Passive solar heating; Passive cooling; Thermal mass)

If thermal mass is used in warm and hot climates to absorb heat from the air, minimise solar gain through glazing and do not locate the mass where it is exposed to solar heat gain.

What is the difference between R-value and U-value?

R-value and U-value are essentially two sides of the same coin. R-value is usually cited when discussing things such as wall and ceiling insulation values. The term does not translate well to windows and other fenestration products. That industry prefers U-values. The two are actually inversely related. The higher the R-value, the better insulated are the walls and ceilings. The lower the U-value, the better job a window does in keeping out the heat and cold.

Eco Timber Windows double glazed  4mm Low-e 18mmARG  4mm           1.1                              0.55

NOTE: These values are indicative only and cannot be used for compliance purposes.

Source: Window Energy Rating Scheme; Copyright owner: The Australian Window Association


 

Design Considerations