Skylight construction consists of three main components: the viewing glass, often called the glazing, the roof curb on which the glass sits and the shaft that directs sunlight into the home. The viewing glass can be constructed of either acrylic or polycarbonate plastic; however, window glass can also be used.
Some homeowners prefer plastic skylights because they are lightweight and economical. However, however plastic glazings do have some design limitations because they are molded. Flat rectangles, domes, bubbles and pyramids are some of the shapes that can be used. Because they are less expensive than glass skylight, they are often good choices, but cracking or potential breakage is possible.
Many homeowners prefer to use glass skylights because they are scratch-resistant and have more design options. With either glass or plastic glazings, the skylight can be constructed with single, double, or triple glazing. Skylight can also be constructed of low-E glass or argon gas-filled panes that will assist in energy efficiency. Thermal resisting skylights will have an R-value rating that is an indicator of the materials resistance to heat flow. The higher the R-value, the better insulating properties the glass has.
The skylight will also have a U-value, which is another indicator of heat flow resistance. However, this rating not only takes into account the glazing material, but also the frame and all related parts. Coatings can also be added to the glazing to block the UV rays of the sun. The rating will be expressed as a percentage of blocked rays. UV blocking will protect carpeting and furniture from sun damage.
While frames are often constructed of solid wood or aluminum, combinations of wood, metal and plastic are becoming more popular. Integrated flashing may be attached to the frame to assist in water resistance; however, additional flashing is often used to ensure protection from leaks.
Another part of the frame, the part you see inside the home, is called the shaft and is often made of plywood, solid wood or vinyl. The shaft can be configured in several ways. Straight shafts will direct the light straight down. The four sides of the shaft can be flared outward, spreading the light over a wider area. For a directional lighting effect, one or two of the shaft sides can be flared and the other sides kept perpendicular.