The small, common stones used as roof ballast possess few individual attributes worthy of extensive examination. But the combined effect of these small stones has been gigantic within the roofing industry.
Ballast enables roofing crews to install large sheets of roof membrane quickly and efficiently in a wide range of weather and temperature conditions. And ballast enables underlying roof membranes to accommodate structural building movement and allows for the direct application of highly efficient thermal insulation boards that might otherwise need to be protected from roofing asphalt or adhesives.
Because of these unique features, hundreds of millions of square feet of ballasted roof systems have been installed throughout North America for nearly three decades. Assuming a service life of 15 to 20 years, it is reasonable to project that nearly 10 billion square feet of ballasted roof systems are currently in service.
Consider what as little as 10 pounds of ballast stone placed on a loose-laid roof membrane can accomplish. If you were to test a roof membrane covered with ballast on a wind-uplift pressure table, the ballast stones would be quickly displaced by the expanding membrane, causing almost immediate roof system failure. But in the field, ballasted roof systems have withstood wind speeds up to 100 mph and equivalent uplift pressures in excess of 45 pounds per square foot.