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How Skylights Work


Integral flashing is built onto the perimeter of some skylights.

By letting natural light stream in, skylights fill rooms with warmth and a feeling of spaciousness. By reducing the need for electrical lighting and adding winter warmth, they also help trim energy bills. And clear ones give you a window to the starry night sky.

A skylight is like a window in the roof, but its frame is designed and flashed to withstand the rigors of rainfall that a roof receives. As shown at right, a skylight’s flashing works in concert with the roofing material to usher away rain and snow.

Though some frames are solid wood or aluminum, most new skylights are made of a combination of metal, vinyl, and wood. The exterior frames tend to be aluminum cladding with a durable finish—the part you see inside is often made of solid wood, plywood, or white vinyl. Newer skylights are virtually leak-free thanks to rugged construction and easy-to-install, integral flashing. They’re also equipped with channels that carry away condensation.

Some skylights are glazed with acrylic or polycarbonate, others with glass. Plastic ones are lightweight, economical choices often put where a skylight could be easily broken. Because they are molded, they come only in standard sizes and shapes: flat rectangles, bubbles and domes, pyramids, ridge- shaped and dormer models, and so forth. Glass is preferred by many people because it doesn’t scratch as readily as plastic does and because it’s available in a vast array of sizes and types.

©Don Vandervort, HomeTips

Skylight flashing provides continuous drainage for water traveling down the roof.

You can get single, double, or triple glazing with energy-saving low-e glass or argon gas–filled panes. For use where the sun may damage carpets and furniture with ultra-violet (UV) rays, you can get bronze-tinted or other UV-blocking glass.

Other options for eliminating or reducing the sun when it’s not wanted include built-in blinds, horizontal curtains, or shades and UV-blocking insect screens.

The cross-section view, at right, of a glass skylight shows key parts and how the flashing provides continuous drainage down the roof.

A skylight’s shaft (see below) governs how light is delivered to the room below. If all four sides are flared, light spreads over a wide area. A shaft with perpendicular sides focuses the light straight below. If the shaft is flared on only one or two sides, it sprays more light in the flared direction.

©Don Vandervort, HomeTips

Different Types of Skylight Shafts

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