All types of roofing systems must meet or exceed insurance and building code requirements. Among these is resistance to fire, which is designated in roof fire ratings. Familiarity with it can help you choose a roofing system that makes your home safer. In this blog, Wortham Bros shares a guide to roof fire ratings.
How Are Roofs Rated?
Roofing manufacturers submit samples of their roofing products to UL Inc., FM Global, or any other certified testing laboratory for certification. The samples undergo test conditions as defined by ASTM E108, which determines a roof’s fire resistance. The tests conducted include flame spread (the narrower the spread, the better the rating), ignition from a burning brand (which simulates embers from a neighboring fire), and exposure to gas flame.
Roofing companies offer products from different manufacturers with varying fire ratings, which are classified as follows:
Class A — Roofing materials with Class A rating is the preferable choice, as it provides the ample protection from major fire-related events such as wildfires. Class A rating requires materials that experience a maximum flame spread of 6 feet, can withstand a burning brand measuring 12 by 12 inches and weighs 4.4 pounds, lasts between 2 and 4 hours before it ignites, and can resist 15 cycles of exposure to gas flame. Materials such as slate, tile and certain asphalt shingle products are generally rated as Class A. Others, like wood shake, may require additional treatment before they meets Class A standards.
Class B — Class B roofing is effective against moderate exposure to fire. Maximum flame spread should be 8 feet, it should be able to withstand a burning brand measuring 6 by 6 inches and weighing 1.1 pounds, lasts 1 hour before ignition, and can resist 8 cycles of a gas flame being turned on and off.
Class C — Class C roofing provides light fire protection, and usually applies to untreated wood shakes and shingles, plywood, or OSB. Maximum flame spread should be 13 feet, it should be able to withstand a burning brand measuring 1.5 by 1.5 inches and weighs 0.009 ounce (0.25 grams), last 20 minutes before ignition, and can resist 3 gas flame cycles.
Unrated Roofing — Unrated roofing materials are those that didn’t pass the requirements for Class C, which means they should be avoided as they can create a false sense of security.