Reducing heat gain through home windows
Some simple considerations to protect windows from heat gain in summer can make your home more comfortable and reduce the costs of cooling your home.
Size and orientation
The size and orientation of your windows will affect the amount of sunlight entering your home. West, east and north-facing windows tend to be exposed to sunlight, while south-facing windows receive almost no direct sunlight. The orientation of your windows also influence how you use coverings and shading. Consider the orientation of your windows if you are planning a renovation.
Frames and glazing treatments
The strength of window frames, together with the glazing component, can greatly affect the energy efficiency of windows. The most energy efficient window frames are made from materials that won’t transfer heat and cold, such as timber, uPVC or combination frames.
Draught-proofing
Heat is both gained and lost from existing houses due to air leakage or draughts. Seal gaps around doors and windows to draught proof your home and save energy and money.
Coverings and shading
Large west, east and north-facing windows should be shaded for increased energy efficiency. External shading is much more effective at keeping your home cool than internal blinds or curtains, as it stops the heat reaching the glass, but using both external and internal window coverings will provide maximum protection.
How to shade windows for summer
The best way to shade your windows depends on which way they face, because the height and angle of the sun changes as it moves through the sky and as the seasons change.
North-facing windows
Fixed horizontal shading devices, such as eaves and pergolas, are ideal for shading north-facing windows. If they are well designed, they can stop the high summer sun from hitting the glass, while still allowing the low-level winter sun to shine in and heat your home in winter. Some pergolas have louvres that can be adjusted to provide complete shading in summer, while still allowing the sun access in winter.
Adjustable external shading, such as blinds, awnings, roller-shutters and conventional shutters, are also suitable for shading north-facing windows in summer. The thicker and more opaque the material, the better the shading effect will be. The external shading should be adjustable to allow the sun in during the winter months and on cooler summer days.
East- and west-facing windows
During summer, east-facing windows can be a major source of heat gain in the morning, while west-facing windows can be a major source of heat gain in the afternoon.
Adjustable external shading devices such as blinds, awnings, louvres or shutters, or angled metal slats provide the flexibility to block the low-angled morning and afternoon sun. Adjustable shading devices allow greater flexibility to make adjustments on a day-to-day or even hour-by-hour basis, in response to changing weather conditions and comfort levels.
Eaves, pergolas and even verandahs provide some benefit, but are not very effective at shading east and west windows as they do not block out the lower-angled early morning and late afternoon sun in summer. If you have a verandah it may be possible to install blinds on the perimeter to shade the windows, walls and verandah itself, making the whole area more comfortable in summer.
Windows that face north-east and north-west are also best shaded by adjustable vertical shading devices such as awnings or blinds.
South-facing windows
South-facing windows receive almost no direct sunlight, so they don't require shading in summer. However, cooling breezes in summer usually come from the south so these windows are useful for cross ventilation. South-facing windows will lose heat from the house in winter unless well protected with either double glazing or heavy curtains and pelmets.
