Tech Today

Concerns with impact testing

In many U.S. regions, the ability of roofing products to resist hail damage is an important performance consideration. Currently, two test methods—UL 2218 and FM 4473—are frequently used to assess products' impact resistances. However, limitations in these test methods may preclude the tests from accurately measuring products' hail-resistance performance.

UL 2218

UL 2218, "Standard for Impact Resistance of Prepared Roof Covering Materials," provides for impact-resistance data for the evaluation of prepared roof covering products. Examples of prepared roof covering products include asphalt, wood, tile, fiber-cement, plastic and metal shingles.

With this standard's test method, a 3- by 3-foot specimen of newly manufactured (nonweathered) roof covering is subjected to impacts from steel balls of varying sizes dropped from specific heights at standard laboratory conditions. The masses of the steel balls combined with the drop heights are said to represent hail's kinetic energy.