Question: Our home tends to be too dark, although we have a number of large windows. Instead of additional lighting, I would like to install a couple of skylights. Rather than rely on information from a sales person, I am seeking your advice on the pros and cons of installing skylights. My neighbor cautioned me that it is almost impossible to install a skylight without creating leaks. Is this true?
Answer: You are wise to investigate this project before proceeding. Although skylights can add sparkle and brightness to a room, as well as improve ventilation (models that open and shut), there are pitfalls to consider. Improperly installed units can leak, which will cause major structural damage. Since skylights admit more light than windows, they can cause problems, such as overheating, too much glare and fading of furniture fabrics. Condensation also can be a problem, particularly in a fixed unit that is installed in a bathroom.
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There are venting or ventilating skylights that help release steam and odors, and promote air circulation. These units, as well as skylight shades, can help in areas where heat and moisture buildup is a problem. Tinted or heat-reflecting glazing is another solution to heat buildup.
Manufacturers make skylights with double or triple glazing, the type used in thermal or insulated windows to control heat gain in summer and heat loss in winter. Multiple glazing also helps prevent condensation on a skylight's surface. Translucent or frosted glazing also is available to help diffuse light and reduce glare.
Plastic skylights come in several shapes, including the common domed type, while glass skylights are flat. Plastic is lightweight and durable, but is more subject to scratching and clouding than glass. This can be important in clear windows but is not as important in diffused windows.
Sizing is important. As a general rule, 1 square foot of skylight illuminates about 20 square feet of floor space. In a home with an unfinished attic above a ceiling of the room where the skylight is wanted, a walled shaft is installed to carry light through the attic to the ceiling below. The spread of light can be controlled by the construction of the walls of the shaft - flared walls to spread the light, straight walls to focus it.
It is important to fit a skylight into the roof with a minimum of cutting and special framing. This helps retain the strength of the roof and also reduces installation time. Often two skylights, positioned almost side by side, will provide the same advantages as a larger unit, but can be installed between standard rafter openings, avoiding cutting through roof rafters and ceiling joists.
Is a dome or flat unit better? A dome will not collect water or dirt and can pick up light from a rising or setting sun. Flat units should be used only on sloping roofs.
Flat or gently sloping roofs can cause problems because of slow runoff of rain water. The bubble-shaped skylights are a good choice for this type of roof because their shape is inherently strong and sheds water.
Another solution is to build a domelike structure to house the skylight and mount it at a steeper angle. Avoid any flush-mounted units, which are installed directly against the roof. The skylight should have a curb or frame that extends above the roof line.
Anytime you cut a hole in your roof, you increase the chances of leaks. However, most skylight leaks are caused by incorrectly installed flashing - a problem that can be avoided. Although flashing techniques can vary between manufacturers, there are some basic installation principles that hold true.
Look for skylights that use a step-flashing system which is made up of identical L-shape pieces that must be installed around the perimeter of the skylight frame. This is the most common in easy-to-install prefabricated models. Unless you have a skylight custom-designed and built, the flashing materials (aluminum, copper or galvanized steel) should be included in the purchase price of the unit. Be wary of any system that relies on caulk for leak-proofing; caulk won't hold up over the long haul.
Probably the best insurance against leaks, condensation and other problems is to select an experienced installer and a high-quality skylight.
Another option to the standard skylight is a solar tube. These are particularly suitable for installation in small spaces, such as your bathroom or a dark hallway. They are less expensive, easier to install, do not leak, won't heat up the room and are energy-efficient.
For interior bathroom installations, you can purchase a ventilation kit that can be used in conjunction with an electric light kit to make a 10-inch solar tube unit an attractive three-in-one unit providing day- and nighttime lighting, as well as ventilation.
When making any purchase, skylights or solar tubes, be sure to read all the instruction manuals, manufacturer guarantees and installation directions. Seek references on prospective installation contractors.
Send e-mail to copleysd@copleynews.com or write to Here's How, Copley News Service, P.O. Box 120190, San Diego, CA 92112-0190. Only questions of general interest can be answered in the column.
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