Choosing the best means for extending roof system service life involves a number of factors. Coatings are one option and can be cost-effective, but their varying performances can create limitations. The reasons a particular coating works in one situation but not another often are complex and difficult to determine. Some limitations of coatings are related to climatic variables.
In the U.S. and Canada, two primary factors seem to dominate regional roofing practices: total annual precipitation and freeze-thaw cycles associated with cold climates. Secondary factors include Hail Belt conditions east of the Rockies, afternoon rain in the Gulf states and Midwest, Florida's tropical characteristics, intense summer temperatures in the Southwest and high winds.
Coatings, particularly those that are water-based, can be affected by moisture in at least two critical ways: They can be worn away by rain or heavy dew or can experience diminished adhesion to damp surfaces. In the eastern half of the U.S., these risks are reduced by using silicone coatings and bituminous-based coatings. ASTM D16, Type V urethanes and new generation polyureas are high-performance and environmentally compliant options when rain is typical or a tough, traffic-bearing membrane is needed.