Stop the sun from passing through your windows and keep the heat out in summer.
Windows can let a lot of heat into your home in summer, especially if you have large unshaded west, east or north-facing windows. It’s better to stop the sun’s heat from hitting the glass than to have to deal with the problem once the heat has already entered you home. The best way to shade your windows depends on which way they face, because as the sun moves through the sky, its height and angle changes.
How to shade 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.
How to shade 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.
While eaves, pergolas and even verandas provide some benefit, they 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.
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.
If you have a veranda it may be possible to install blinds on the perimeter to shade the windows, walls and veranda 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 receive almost no direct sunlight, so don’t require shading in summer. However, the cooling breezes in summer usually come from the south so they 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 or pelmets.
How to select energy efficient glazing
The type of glazing you choose can help you to keep the heat in during winter while also keeping the heat out in summer.
Windows consist of glazing and framing. Both components contribute to the overall performance of the window, which is called a U-value. U-values measure the amount of heat passing through a glazed unit in watts; the lower the U-value, the more energy efficient your window is. In your home, you should aim to use windows with low U-values because they will be more effective at keeping out any unwanted heat and cold.
Selecting glazing for new windows
Double or triple glazing: Double glazed windows are very energy efficient, as they can reduce heat loss or heat gain by almost 30% in comparison to single-glazed aluminium windows. Triple-glazing performs even better than double glazing and is ideal for the colder climates.
Low emittance glass (Low-E glass): Emittance is a measure of how much radiant heat a material absorbs and emits. As low-e glass reduces solar gain in winter as well as summer, it is not generally recommended for sun control and is more appropriate for complementing double glazing to reduce winter heat loss through windows. Adding a low-e coating to the internal pane of glass will help to make your house warmer in winter.
Secondary glazing for existing windows: Secondary glazing can be retrofitted to existing windows through the addition of an extra pane of glass or clear acrylic fitted to an existing single glazed window. Secondary glazing can be attached through magnetic strips or built onto the existing frame, and is often a cheaper alternative to double or triple glazing. Depending on the product and its ability to create an air space between the existing window and the second layer, they may be able to mimic the properties of a double glazed window.
Secondary glazing treatments are a popular solution for improving the energy efficiency of heritage windows, as they maintain the existing character.
Glazing films for existing windows
There are also a range of magnetic and transparent films on the market that can be fitted either to the frame or the glass of an existing window. The glass can also be treated to reduce the amount of solar energy lost through it. Some glass treatments reduce heat gain and the amount of light in winter as well as in summer. Common products are:
Toned glass, in which a tint is applied to the glass during manufacture to reduce the amount of heat transmitted through it.
Reflective coatings, which can be applied to new and existing windows. These tend to stop greater amounts of heat gain than some toned glass.