The primary goal in cooling is to avoid experiencing heat. Keep the sun out, let cool breezes in, turn off your lights and appliances, and seek the coolest spot indoors or out. The summer sun is a potent heat source; it affects your house primarily on
Stay Cool in the Shade
Being in shade is one of the best ways to avoid the sun’s heat. Windows are far more vulnerable to summer sun than walls or roof; they account for 40–50% of a home’s unwanted heat. Shading outside these windows will stop the sun before it strikes the glass.
Overhangs, Awnings, Blinds, Screens
At south windows, awnings or long roof overhangs can block the high-noon summer sun. It’s generally easier to install awnings than to add a roof overhang to an existing house.
For east and west windows, awnings, exterior roll blinds, or shade screens can be effective. If you also have a roof overhang, you might be able to preserve the view by installing a shade screen over the lower half of the window, while the overhang protects the upper part. Exterior blinds and screens will probably need to be secured against strong winds, and should be easily removable for cleaning.
Interior blinds provide some shading, but when the sun penetrates the glass, its heat has already entered your home. However, interior blinds have some advantages. They’re easier to maintain, they aren’t buffeted by winds, and they stay much cleaner. They are also easy to control from inside, and they bounce sunlight up toward the ceiling rather than into your eyes. For best performance, the exterior side of the blind should be white, to reflect the sunlight outward.
Shrubs and trees are a beautiful way to shade your windows. You’ll get the greatest benefit by selecting, placing, and maintaining them with a few pointers in mind:
Trees can cast shade over a wide area, creating a cooler microclimate below them. Deciduous trees allow some winter sun to penetrate when they lose their leaves, which is usually an advantage. Trees and shrubs also emit water vapor, which lowers the air temperature near them while raising the humidity (more desirable in dry than in humid climates). And when trees sway and rustle with the breeze, it’s a psychological reminder of their cooling effect.
Trellises act like living awnings and are especially effective for shading. They can be attached to the house or stand clear of it. They can support deciduous vines that keep their leaves until cool weather begins in late fall and then stay leafless until warm weather begins in late spring. This is especially important for shading south windows; the sun’s path is identical at the equinoxes, but September is usually warm, while March is usually cool.
The trellis vine celebrates seasonal change. If you choose the right species, you’ll get fragrance, color, and edible fruit. But the trellis can’t be adjusted on a daily or hourly basis, while an awning can. A hot spell after leaves have fallen in October, or a cold spell after leaves have appeared in May, can leave you without the shade or sunshine you want.
A trellis shading south windows needs to be high enough to allow winter sun to fully strike the window, and deep enough to fully shade the window in summer. This also applies to roof overhangs.
A Refreshing Breeze
Cool breezes are often welcome to relieve stuffy rooms—as long as they don’t carry pollen or fumes. Moving air is beneficial in summer, because it helps our bodies lose heat by evaporating sweat, and by removing heat buildup from our homes.
Getting the breeze through your home is a four-step process:
How much window area do you need? Generally, the windward side of your home (the side the wind hits) should have a total openable window area of about 7% of the total floor area, and the opposite (leeward) side should also have about 7%. Internal walls should have a similar open area to avoid obstructing airflow. (Close down your exterior openings as the wind speed increases or the outdoor temperature drops.) This type of cooling is called cross-ventilation.
Window type matters, too. Casement windows cranked entirely open admit nearly all the breeze. Double-hung, single-hung, and sliding windows admit about half the breeze, and awning windows admit about three-quarters.
Screens stop insects, but they also reduce the velocity of the breeze. The dirtier they get, the more they reduce it, so wash your screens often.
Does the wind usually come from one direction in hot weather? (If you’re unsure, see Climate Consultant in the Resources section.) If so, you can use shrubs to direct breeze toward your windows. They can be planted in a V shape, spreading out from the windows that admit the breeze, or from that entire side of the house. If the wind strikes the opening at a diagonal, the shrubs just downwind of the opening can divert flow into the window.
Shrubs can also bring fragrance, and their leaves may rustle in the breeze, reassuring you that cooling is happening. In dry summer weather, misting the shrubs will give you an added touch of cooling by evaporation.
Warm air rises, so to let it out, open the windows highest in your house. Then open the lowest windows. The resulting airflow uses the stack effect, whereby outgoing hot air is replaced by incoming cool air from below. This is particularly effective in two-story homes with basements, because the house’s height creates a stack effect that slowly draws the cooler basement air up to cool the ground floor. The highest opening should not face into the prevailing summer wind, or the warm air may be blown back down into the house.