ABOUT SKYLIGHTS Ventilation, views and light Skylights come in many forms, from inexpensive plastic domes to operable roof windows that double as rooftop emergency exits. Even the most basic skylight admits daylight into interior spaces that otherwise would have to be illuminated electrically. Skylights that open and close have the added advantage of venting stuffy air from upper story rooms. Depending on how they are placed, skylights also can provide great outdoor views. Both plastic and various kinds of glass are used for skylight glazing. Plastic, usually acrylic or polycarbonate, costs less than glass, but it’s not as resistant to scratches and after long exposure to sunlight it may become brittle and discolored. Polycarbonate has higher impact resistance and is more expensive than acrylic. Plastic skylights are manufactured in a variety of shapes — domes, rectangles, circles, ovals, and triangles — that would be difficult to duplicate with glass. More expensive skylights are made with glass, and manufacturers now offer a tremendous variety of glazing options. That can be useful in choosing skylights for a particular roof location, or for a particular climate zone. Skylights are manufactured by many companies, although there are only a few national players. The residential market for off-the-shelf skylights is dominated by Velux, a Danish company. Maine-based Wasco claims a distant second place. Other manufacturers, such as Tam, Columbia,and Sun-Tek, are stronger regional forces. Fakro, is a major European manufacturer but it hasn’t made serious inroads in the U.S. to date. Three major window manufacturers ( Andersen, Marvin and Pella) have dropped out of the skylight business in recent years as the industry consolidated. In addition to mass-marketed residential skylights, there’s also a booming trade in high-end custom skylights for residential as well as commercial buildings. Wasco considers itself the leader in that field. Matching…