Two excellent methods to block heat are insulation and shading. Insulation helps keep your home comfortable and saves money on mechanical cooling systems such as air conditioners and electric fans. Shading devices block the sun’s rays and absorb or reflect the solar heat.
Weatherization measures—such as insulating, weatherstripping, and caulking— help seal and protect your house against the summer heat in addition to keeping out the winter cold. For more information on weatherizing your home, see the Energy Efficiency and Renewable Energy Clearinghouse (EREC) fact sheet Caulking and Weather-stripping and the U.S. Department of Energy (DOE) fact sheet Insulation.
The attic is a good place to start insulating because it is a major source of heat gain. Adequately insulating the attic protects the upper floors of a house. Recommended attic insulation levels depend on where you live and the type of heating system you use. For most climates, you want a minimum of R-30. In climates with extremely cold winters, you may want as much as R-49. Again, check the DOE fact sheet Insulation on how to determine the ideal level of insulation for your climate.
Wall insulation is not as important for cooling as attic insulation because outdoor temperatures are not as hot as attic temperatures. Also, floor insulation has little or no effect on cooling. Although unintentional infiltration of outside air is not a major contributor to inside temperature, it is still a good idea to keep it out. Outside air can infiltrate your home around poorly sealed doors, windows, electrical outlets, and through openings in foundations and exterior walls. Thorough caulking and weatherstripping will control most of these air leaks.
Shading your home can reduce indoor temperatures by as much as 20˚F (11˚C). Effective shading can be provided by trees and other vegetation and exterior or interior shades.
Landscaping is a natural and beautiful way to shade your home and block the sun. A well-placed tree, bush, or vine can deliver effective shade and add to the aesthetic value of your property. When designing your landscaping, use plants native to your area that survive with minimal care.
Trees that lose their leaves in the fall (i.e., deciduous) help cut cooling energy costs the most. When selectively placed around a house, they provide excellent protection from the summer sun and permit winter sunlight to reach and warm your house. The height, growth rate, branch spread, and shape are all factors to consider in choosing a tree. Vines are a quick way to provide shading and cooling. Grown on trellises, vines can shade windows or the whole side of a house. Ask your local nursery which vine is best suited to your climate and needs.
Besides providing shade, trees and vines create a cool microclimate that dramatically reduces the temperature (by as much as 9˚F [5˚C]) in the surrounding area. During photosynthesis, large amounts of water vapor escape through the leaves, cooling the passing air. And the generally dark and coarse leaves absorb solar radiation.
You might also consider low ground cover such as grass, small plants, and bushes. A grass-covered lawn is usually 10˚F (6˚C) cooler than bare ground in the summer. If you are in an arid or semiarid climate, consider native ground covers that require little water. For more information on landscaping, see the EREC fact sheet Landscaping for Energy Efficiency.
Both exterior and interior shades control heat gain. Exterior shades are generally more effective than interior shades because they block sunlight before it enters windows. When deciding which devices to use and where to use them, consider whether you are willing to open and close them daily or just put them up for the hottest season. You also want to know how they will affect ventilation.
Exterior shading devices include awnings, louvers, shutters, rolling shutters and shades, and solar screens. Awnings are very effective because they block direct sunlight. They are usually made of fabric or metal and are attached above the window and extend down and out. A properly installed awning can reduce heat gain up to 65% on southern windows and 77% on eastern windows. A light-colored awning does double duty by also reflecting sunlight.
Maintaining a gap between the top of the awning and the side of your house helps vent accumulated heat from under a solid-surface awning. If you live in a climate with cold winters, you will want to remove awnings for winter storage, or buy retractable ones, to take advantage of winter heat gain.
The amount of drop (how far down the awning comes) depends on which side of your house the window is on. An east or west window needs a drop of 65% to 75% of the window height. A south-facing window only needs a drop of 45% to 60% for the same amount of shade. A pleasing angle to the eye for mounting an awning is 45˚. Make sure the awning does not project into the path of foot traffic unless it is at least 6 feet 8 inches (2 meters) from the ground.
One disadvantage of awnings is that they can block views, particularly on the east and west sides. However, slatted awnings do allow limited viewing through the top parts of windows.
Louvers are attractive because their adjustable slats control the level of sunlight entering your home and, depending on the design, can be adjusted from inside or outside your house. The slats can be vertical or horizontal. Louvers remain fixed and are attached to the exteriors of window frames. Shutters are movable wooden or metal coverings that, when closed, keep sunlight out.
Shutters are either solid or slatted with fixed or adjustable slats. Besides reducing heat gain, they can provide privacy and security. Some shutters help insulate windows when it is cold outside. Rolling shutters have a series of horizontal slats that run down along a track. Rolling shades use a fabric. These are the most expensive shading options, but they work well and can provide security. Many exterior rolling shutters or shades can be conveniently controlled from the inside. One disadvantage is that when fully extended, they block all light.
Solar screens resemble standard window screens except they keep direct sunlight from entering the window, cut glare, and block light without blocking the view or eliminating air flow. They also provide privacy by restricting the view of the interior from outside your house. Solar screens come in a variety of colors and screening materials to compliment any home. Although do-it-yourself kits are available, these screens will not last as long as professionally built screens.
Although interior shading is not as effective as exterior shading, it is worthwhile if none of the previously mentioned techniques are possible. There are several ways to block the sun’s heat from inside your house.
Draperies and curtains made of tightly woven, light-colored, opaque fabrics reflect more of the sun’s rays than they let through. The tighter the curtain is against the wall around the window, the better it will prevent heat gain. Two layers of draperies improve the effectiveness of the draperies’ insulation when it is either hot or cold outside.
Venetian blinds, although not as effective as draperies, can be adjusted to let in some light and air while reflecting the sun’s heat. Some newer blinds are coated with reflective finishes. To be effective, the reflective surfaces must face the outdoors.
Some interior cellular (honeycombed) shades also come with reflective mylar coatings. But they block natural light and restrict air flow. Opaque roller shades are effective when fully drawn but also block light and restrict air flow.