Long considered one of the more durable and sustainable steep-slope roof covering materials, clay and concrete roof tile products have been becoming more energy-efficient and environmentally friendly. The development of lightweight and cool-colored tiles has resulted in increased availability of tile roof systems on existing structures and the use of tile roof systems to achieve energy-saving goals.
To be classified as lightweight, tile roof covering material must weigh less than 6 pounds per square foot (psf) at oven-dry weight. A key factor in the design and performance of lightweight tile roof systems is a tile's water absorption property. Water absorption can increase a tile system's weight after a rainfall and possibly affect a building's structural integrity. For example, a tile product that weighs 5 psf at oven-dry weight and has a 10 percent water absorption rate by weight will weigh 6.05 psf when wet.
A lightweight tile load of less than 6 psf allows tile to be used as a roof system replacement on existing structures often without requiring a structural load analysis per local building departments. However, lightweight tile may sacrifice strength and low water absorption properties to achieve the required light oven-dry weight; therefore, the use of lightweight tile is not recommended for all geographical areas. Locations where lightweight tiles generally are not recommended include regions of freeze-thaw cycling, moderate to heavy rainfall and frequent hail.