Shade Your Windows

Quick Facts Affordability Cost Savings CO2 Reduction		Using internal blinds and drapes can block up to 65% of the heat that would otherwise come in through your windows. External shade screens can block up to 95% of the heat. The more glass your home has – especially on the east, west and south sides – the more important window shading is to enhance comfort and reduce energy use. Affordability Window coverings vary widely in price. They do not need to be expensive to provide insulation. Long-term savings from improved cooling and heating efficiency can largely offset the initial costs. Cost savings Window coverings will regulate your home's temperature and reduce your energy use year-round. As well as keeping your space cooler in the summer, internal shading devices will also work to keep it warmer in winter. Health & comfort Naturally regulated indoor temperature is more comfortable and healthier to live in than an air-conditioned environment. Environmental considerations Minimize the ecological impact of the window coverings you purchase: Choose blinds made from fast-growing cellulose materials, such as bamboo or Forest Stewardship Council (FSC) certified woods. Avoid fabrics likely to have had toxic treatments, such as bleached cotton or synthetics. Do not purchase permanent-press curtains as they will contain formaldehyde. As well, avoid stain-resistant and water-resistant features, as they will likely contain toxic chemicals, such as perfluorochlorinated compounds. Ensure your selection criteria accounts for the energy and toxins used in manufacture, as well as disposal options. Some materials, in particular vinyl, are toxic to produce and dispose of.

What you need to know

Interior

• During the day, close curtains and blinds over sunny windows to keep heat out.
• Open blinds and windows at night to circulate air and cool your home.
• Horizontal blinds with the leading (inside) edge tilted upwards will block heat from entering while allowing light in.
• In general, the closer your window coverings are to the window, the more effective they will be as insulators.
• Thermal-lined curtains maximize cool air retention and heat-blocking abilities in summer, and minimize heat loss in the winter.
• Curtains tend to be more effective insulators (for both heat gain and heat loss) than blinds.
• Curtains will insulate better with a seal at top (valance) and bottom (window sill) to stop air from flowing above or beneath them. Sizing curtains with a wide sweep to either side of your windows will also improve their insulating ability.
• Keep south facing and west-facing windows closed when the sun is on them.

Exterior

• If you get strong heat rays through some windows in the summer, use awnings or external shade screens to keep the heat from reaching those windows.
• Shading south-facing windows with a well-positioned overhang or external awning is the most effective way to reduce summer heat gain. Removable awnings allow for maximum light and heat gain in winter.
• Exterior awnings or shade screens can prevent up to 95% of the sun's heat from coming through sun-exposed windows. To ensure correct positioning, you need to observe the sun's path on your house during the summer as well as key areas of heat gain. Overhangs on the west side do not do much as the sun will be horizontal in the late afternoon and early evening in the summer.
• Most shade screens are lightweight and easy to install. Alternatively, attach bamboo blinds to the outside of windows to block heat.
• One benefit of using overhangs or awnings instead of a window screen is that overhangs allow natural light to come in. If you block the window, lights may be required inside, which will use additional energy.
• Other than overhangs, use external shading equipment that can be removed for the winter, especially on windows with southern exposure. South-facing windows can be a source of free solar heat in winter.
• Low emissivity, or Low-E, windows are another way to block heat before it enters. A Low-E coating is a thin, transparent layer in the glass of a window that reduces the amount of energy (heat and ultraviolet rays) able to pass through in either direction. It also protects furniture and fabrics from fading.
• You can gain similar benefits by using window tints, which are thin films that are applied to windows. For best results, you can hire a professional, but many of them are fairly easy to install. Select tinting material that will withstand seasonal temperature variations. Tints start working the moment they are applied, reducing solar heat and glare, and protecting furniture from fading.
• Check out Get Energy Efficient Windows for more information about energy efficient windows.
• Anything that reduces solar gain in summer will also block valuable solar heat gains in winter. Unless summer heat is a greater problem in your home than winter cold, a removable external shade device is likely a better option for year-round energy efficiency.
• In addition to window shading, repainting and/or re-cladding the exterior of your house with light-coloured material will reduce solar radiation absorption.
• Landscaping, in particular planting deciduous trees to shade south and west windows, is another efficient way to shade windows and keep your home cool in warm weather. Read our Plant a Deciduous Shade Tree tip for more information.
• Interior window coverings that keep you cool can also keep your home warm in cold weather. See our Home Heating Green Guide for more information.

FAQ

Will my house have to be dark all day if I use curtains and shades to keep it cool?
No. You don't need to keep curtains and shades closed over all your windows. North-facing windows and south-facing windows protected with awnings will usually let light in, but not heat. You can open the curtains on windows when the sun is not shining on them directly, especially in the mornings and evenings. If you have tall windows and the sun only shines through the lower portion, cover the lower part of the window, leaving the tops open to allow light in.

What is passive cooling?
Passive cooling uses non-mechanized techniques to keep cool and reduces, or even eliminates, the need for air conditioning. Passive cooling includes using features like overhangs for south-facing windows, shade trees, having few windows on the west side, and using thermal mass (see question below) and cross ventilation. For example, a well-designed overhang works by shading a window in the heat of the summer, but allowing sunlight to penetrate the interior of a house in winter.

Some people say not to have pavement on the south side of a house and others say it works as an energy-efficient thermal mass. Which is correct and what does thermal mass mean?
You don't want to put non-permeable, unshaded pavement on the south side of your house because in the summer it will heat up and reflect that heat indoors. However, an area of rock or concrete, which is shaded in summer and exposed in winter, can act as a beneficial thermal mass, radiating heat into your home in the winter and cool air in the summer. A thermal mass can also be water or any other material that will absorb heat and coolness. Proper use of a thermal mass is an important passive heating and cooling technique. Thermal mass stores heat in the winter to release in the evening and works in reverse in the summer. The mass cools down in the evening and retains that coolness the next day, moderating the effects of high daytime temperatures.