ABSTRACT
Asphalt-glass fiber built-up roofing membranes are composed of alternate layers of glass fiber felt and relatively high melting point asphalt. Three to four layers of glass felts are often used. The top surface is coated with asphalt, asphalt emulsions, or asphalt and gravel or slag. The gravel functions as ballast to hold the roof in place, to protect the asphalt from degradation due to radiation, and to improve the system’s fire resistance. The asphalt and gravel finish is most frequently used. Properly adhered or fastened gravel surfaced built-up roofs are seldom displaced by the wind, unless the structure that supports them fails. Select an aggregate that complies with ASTM D1863 Standard Specification for Mineral Aggregate Used on Built-Up Roofs. Try not to use relatively fine gravel such as pea gravel. Pea gravel is too easily displaced by wind scour, and if applied at ~20 kg/m2 (~400 lb/100 ft2), much more than 50 percent of the surfacing will be loose and subject to wind scour. The aggregate’s value as ballast is decreased if the quantity of pea gravel applied is reduced.
