Roof fire ratings are either Class A, B, C, or unrated depending on whether a roof covering does not meet these requirements. Unrated is the most dangerous. Class A is the highest rating and offers the greatest resistance to fire. Concrete or clay roof tiles, metal roofs, and fiberglass asphalt composition shingles are all examples of Class A roofing. Untreated wood shake roofs are an example of an unrated cover. Wood shakes and shingles that have been treated with fire retardant chemicals can be given a Class B rating. Additional materials may also be included in the roof assembly to meet this requirement.
To determine the roof covering’s fire rating, a standard fire test must be used. The following criteria are evaluated:
- Flame penetration through the roof covering into an attic space.
- Flame spread across the roof surface.
- The propensity of the roof cover to become detached and produce embers.
Roof coverings that require special installation techniques or an underlying material to increase their fire rating may rely on roof coverings. Roof coverings that have to be covered with additional material will often get a “by-assembly” fire rating, rather than a “standalone” fire rating. The roofing manufacturer may require that the fire rating is obtained. This means that additional material and instructions must be included in the test. Aluminum roof coverings and fire-retardant treated wooden shakes are examples of by-assembly fire ratings. A shake roof that has been treated with fire retardant can have a standalone Class B rating.
This post was written by Ted Williams! Ted is the owner of A Old Time Roofing, one of the best roofing companies in Saint Petersburg, FL! Ted is a Master Elite Weather Stopper GAF Roofing Contractor, a double award winner of Best Steep-Slope Contractor from GAF and achiever of Master Elite Consumer Protection Excellence from GAF. He has been serving the Pinellas County area since 1978. Old Time Roofing has a tradition of quality workmanship, servicing residential and commercial properties.