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
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...
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