Windows and shading
More heat is gained and lost through windows and other glazed surfaces in an average insulated home than any other aspect of the building fabric. Choosing the right size windows and the right glazing material can significantly improve the comfort and efficiency of your home.
Shading is an effective way to keep your house cool in summer, but needs to be well-designed so that it does not block out warming winter sun. Done well, shading can help lower your heating and cooling appliance use.
Window size and location
Ideally, north facing windows should be full length to allow the heat from the winter sun in. East and west facing sides should have a minimum area of glass, or none at all, to help keep summer heat out.
Sunlight shining directly on north, east and west facing windows produces the same amount of heat per square metre as a one bar radiator.
As a general guide, the total window area should be less than 25% of the total floor area of the house. A guide to the percentage of window area to wall area for each direction is:
- north facing 60%
- south facing 30%
- east facing 15%
- west facing 0-7%.
The Australian Government’s YourHome website provides detailed information about glazing and thermal performance of your home, including:
- different types of glass
- solar heat gain
- window films and frames
- choosing the right window for your home
- design considerations
External shading should be designed to let in the winter sun but totally shade the summer sun. External shading can include:
- correctly designed eaves
- horizontal shades or awnings
The Australian Government’s YourHome website provides detailed information about external shading for your home, including:
- general guidelines for shading
- calculating sun angles
- fixed and adjustable shading
- plants and landscaping for shading.
Internal shading, such as curtains and blinds, is not as effective as external shading for preventing the sun's radiant heat from entering the home. However, it is a good alternative if you can’t install external shading. If you do not want to obstruct a view, use tinted or reflective glass.
To reflect sunlight in summer, internal curtains and blinds should have a light coloured backing. The space between the blind and window traps heat, so opening a window slightly can help this heat to escape.
In winter, curtains and blinds that have pelmets will help to keep heat inside the home and prevent warm air from coming in contact with the cold glass.