Skylights and roof windows can provide interior building spaces with the warmth and brightness of natural daylight. Their ability to enhance almost any interior has made them increasingly popular. However, installing a trouble-free, energy-efficient skylight can be very difficult. In order to gain the maximum benefit from a skylight, it is important to understand designs, materials, positioning, and proper installation.

Designs

Skylights are available in a variety of shapes and sizes. Some open for ventilation, others are fixed. Larger skylights that can be used as doors are sometimes called "roof windows." Roof windows are always located within a few feet of the floor.

The most common shape for a skylight is rectangular, but they are also available in circular, oval, diamond, triangular, and multi-sided configurations. Non-rectangular units usually use plastic glazing, though higher quality units use glass. The glazing can be flat, arched, domed, pyramidal, and "warped plane" (the glazing is flat on the low side and concave in section on the high side). Of these, the pyramidal, arched, and domed shapes offer flexibility in placement. Their raised design allows light to enter from more extreme angles than flat or warped plane units. This allows more positioning options. The slope or curvature of the glazing also helps to shed moisture and leaves. These skylight designs also do not require the additional framing needed to slope a flat skylight for proper drainage on flat or low-slope roofs.

Skylights can provide ventilation as well as light. Ventilating a building through a skylight opening releases the hot air that naturally accumulates near the ceiling. Ventilating skylights usually open outward at the bottom, some more than others. Some units vent through a small, hinged panel. One design uses a swing-down, inner sash with a protected vent strip above. This can reduce the potential for rain or snow entering the room if the vents are open. Skylights may be opened manually with a pole, chain, or crank. Automated units with electric motors or pneumatic devices are also available, and some models incorporate moisture sensors to automatically close the skylight when it rains.

The physical size of the skylight greatly affects the illumination level and temperature of the space below. Use the following "rule of thumb" for sizing a skylight: the skylight size should never be more than 5% of the floor area in rooms with many windows and no more than 15% of the room's total floor area for spaces with few windows.

In very cold weather, skylights are often prone to water vapor condensing on the glazing. The accumulation of water may then drip into the room. Better skylights usually have an interior channel to collect the condensate so it can evaporate later. The most thermally efficient skylights (R-4 or greater) are less prone to condensation problems.

Recent, "high tech" developments maximize skylights for daylighting. An "element" on the roof becomes an aperture for collecting sunlight. It may be a sun-tracking open-sided cylinder, a large lens-like element, or merely a conventional skylight with a mirrored reflector mounted adjacent to it. This aperture may then connect to a mirrored pipe, or "light pipe," which has a diffusing lens that mounts on or is recessed into the ceiling of the room below. These designs, relative to equivalent traditional skylights, effectively reduce daytime overheating and nighttime heat loss, but do not provide views or ventilation.

<< Previous    [1]  2  3  4    Next >>