Around this time of year, when the sun is beating down on thousands of school roofs, facility managers are looking for ways to stay cool. One way to do that is to keep school buildings from absorbing the heat from those intense summer rays. And it's up on the roof where that heat is absorbed — or reflected, if a school or university has installed a cool roof on the facility.
A cool roof is made of materials that are able to reflect much of the sun's energy from a roof surface. For the low-slope roofs that are found on most school facilities, cool roofs are mainly bright white in color, the Cool Roof Rating Council says.
A guide from the U.S. Environmental Protection Agency, “Reducing Urban Heat Islands: Compendium of Strategies,” says that for low-slope roofs, the two primary cool-roofing options are coatings and single-ply membranes. Typically, the guide says, a cool roof coating is used if an existing roof needs moderate repair, and a single-ply membrane is used for more extensive repairs.
Coatings “have the consistency of thick paint and contain additives that improve their adhesion, durability, suppression of algae and fungal growth, and ability to self-wash, or shed dirt under normal rainfall,” the guide says.
The cool roof coatings can be applied to many existing surfaces, including asphalt capsheet, gravel, metal and various single-ply materials.
The common single-ply membrane materials used for cool roofs are EPDM (ethylene propylene diene monomer), CSPE (chlorosulfonated polyethylene), and PVC (polyvinyl chloride) and TPO (thermoplastic olefins).
“The materials are generally glued or mechanically fastened in place over the entire roof surface, with the seams sealed by taping, gluing, or heat-welding,” the guide says.
The benefits of a cool roof, the Cool Roof Rating Council says, include reduced summer air-conditioning costs, reduced costs for roof maintenance and replacement, a reduction of the heat-island effect in cities and suburbs, reduced air pollution and smog formation, and reduced roofing waste added to landfills.
The Council says that one potential drawback of cool roofs is that they can increase heating costs in winter months. However, the increase is usually small because in most of the nation, the sun is low in the sky in the winter, the weather tends to be overcast, and snow often covers roofs, the council says. So the increase seen in winter months usually is outweighed by the cooling energy saved in the summer.
NOTABLE
50 to 60
In degrees Fahrenheit, the difference in temperature
between a roof made with traditional materials and a roof with highly reflective and emissive materials.
10 to 70
In percent, the
reduction in cooling energy on buildings that have cool roofs.
0 to 20
In cents per square foot, the estimated cost premium for cool roof products.
Source: U.S. Environmental Protection Agency, “Reducing Urban Heat Islands: Compendium of Strategies”
