What Are the Round Domes on the Roof of a House?

Dome Skylights

• Dome-shaped skylights are among the most flexible for positioning, according to the U.S. Department of Energy. This is because the curvature of the dome allows light to enter from far more angles than is possible with flat skylights. The curvature also helps the skylight to be self-cleaning; it sheds moisture and leaves easily. Dome-shaped skylights often are connected to reflective metal tubes that efficiently bounce light down into living spaces. These are called tubular skylights and come in many sizes. It is possible to cluster a number of tiny dome skylights to flood a room with light. The Department of Energy notes that tubular skylights are efficient at limiting heat gain in summer and and energy loss in winter.

Turbine Vents

• Turbine vents look a little like a turban or a chef's hat with a pleat-shaped dome atop a short column. They are also called whirlybird vents because of the way they spin in the wind. The pleats are the blades of the turbine that are designed to draw air out of an attic when wind blows on them. In the summer, it releases hot air; in the winter, it helps moist air escape that would otherwise damage the entire house. Turbine vents are about 18 to 20 inches tall.

Turbine Vent Power

• Tim Carter of the Ask the Builder website says a 12-inch-diameter turbine vent can suck out 347 cubic feet of air per minute when wind travels at a constant speed of 5 miles per hour. At that speed, Carter says, a single 12-inch turbine vent can change out all the air in an attic in 52 minutes. Despite being wind-driven, turbine vents are sometimes called static vents.

Static Vents

• Depending on their placement, static vents either draw in fresh air or exhaust air from attics. They are referred to as being static, because they don't require electricity as roof fans do. Static vents used to exhaust air are placed close to the ridge line of a roof. Some are short tubes with squat, dome-shaped lids that help keep rain, debris, bats and insects from penetrating the louvers or mesh at the top of the tube. Occasionally, fan-driven vents will also have dome-shaped covers. Other shapes of static vents include the flat, mesh-backed, fresh-air intakes installed on the underside of roof eaves.