Domed acrylic skylights are less expensive than glass, and their convex shape tends to let the rain wash accumulated dust and dirt off a little easier. The acrylic dome is mounted in an aluminum frame, which is in turn mounted on a 2x6 box called a "curb." Once the hole is cut in the roof to the manufacturer's specifications, the curb is constructed on-site to raise the skylight above the level of the roof sheathing. Site-built or factory-supplied flashings are used to seal the roofing around the curb.
Domed skylights are available in clear, smoked, bronze or other tints. Most are double- or triple-glazed in order to achieve the level of energy efficiency required by the building codes. Several sizes are available, with the most common being 2x2, 2x4 and 4x4 feet.
Flat glass skylights come mounted in a wood or integrated rubber and metal framework, and require no additional curb construction. After the hole is cut, the skylight frame is simply attached to the roof sheathing with L-brackets, then the installation is completed using the factory-supplied flashing kit. Ease of installation, superior insulating qualities, less tendency to scratch and a cleaner finished appearance all add to the popularity and somewhat higher cost of glass skylights.
Glass skylights also have a greater number of optional accessories. These include tempered, laminated or wire glass; shades and blinds for light control; glass tints for heat retention or to block sunlight; and the ability to open fully or partially for ventilation. At least one company, Velux - a leading manufacturer of quality glass skylights that are available at most local home centers and lumber yards - even offers an electric motor coupled to a rain sensor that automatically shuts the skylight if it detects rain.
LIGHT SHAFTS
If the room you intend to illuminate with the skylight has an open ceiling with no attic space above, you can install the skylight without needing to construct a light shaft. This is by far the simplest installation, and it offers the maximum amount of light and a view of the sky. Operable units are usually recommended, especially for a second-floor room, since these direct skylights can add a considerable amount of heat to the room on a summer day.
For ceilings with an attic space above, a light shaft must be constructed that connects the skylight to the room. Skylight shafts take one of three forms:
--Straight, in which the shaft drops vertically from the roof to the ceiling and is the same dimension as the skylight itself. This type is the easiest to construct, but because of its offset angle relative to the skylight, offers the least amount of light.
--Angled, where the shaft is parallel to the pitch of the skylight. It, too, is the same dimension as the skylight, but its straight-in angle offers more light than a straight shaft. Angled shafts also are used to connect two locations that cannot otherwise be aligned. This occurs when the skylight must be installed in a particular spot - between two trusses, for example - and the shaft opening is likewise limited to a particular location on the ceiling that is not directly under the skylight.
--Splayed, or pyramid, in which the ceiling opening is larger than the skylight opening in width, length or both. This type, although a little harder to construct, is the most popular, simply because it allows a smaller skylight to illuminate a larger area.
After the skylight is installed, you'll need to position and mark the opening on the ceiling. Take into consideration the size of the room and the amount of light you wish to bring in, and select the size and position of the hole accordingly.
Once the skylight is installed and the ceiling hole is cut, it's then a matter of connecting the two with the shaft, which is constructed from 2x4 or 2x6 lumber. The angles involved typically require some tricky framing, and is probably best left to an experienced carpenter.
After the framing is completed, the inside of the shaft is covered with wood or drywall, and the attic side is insulated to at least R-21 to minimize heat loss. To reflect an even greater amount of light into the room, consider painting the inside of the shaft with gloss or semi-gloss white paint.

Copyright 2003 Inman News Features