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Roof Fire Ratings

Roof Fire Ratings, roof replacement austinUnderwriters Laboratories, a for-profit but independent company, was founded in 1894 for the primary purpose of testing the safety of products and certifying the results. Soon after its founding, UL began publishing safety standards, evaluating manufacturers’ claims and conducting inspections in addition to testing and certification. Roof Fire Ratings for roofing systems are provided by UL and cover the resistance to fires originating from an exterior source. Roofing materials may be rated as Class A, Class B or Class C, but there is also a category for unrated materials.

Roof Fire Ratings

Class A

Class A roofing materials provide the greatest resistance to fires. Fiberglass asphalt shingles and most metal roof coverings qualify for this class, but they must be applied according to the manufacturer’s specifications for installation, component materials and roof preparation. Many municipal codes require homeowners to use Class A roofing systems, especially in heavily wooded areas that are prone to high winds, drought or wildfires. To earn this rating, the roof must pass the following tests.

• Withstand a 12-inch by 12-inch burning brand that weighs 2,000 grams
• Resist ignition for two to four hours
• Have a flame spread of no more than 72 inches
• Resist a gas flame that is turned on and off 15 times

Class B

Class B roofing offers resistance to moderate fire exposures. An example of a roof covering in this class is a shake roof that has been treated with a fire retardant. However, if combined with certain underlying components, including some roll roofing, the shakes may qualify as Class A. To be rated as a Class B roofing material, the test requires the roofing to pass the following requirements.

• Withstand a 6-inch by 6-inch burning brand that weighs 500 grams
• Resist ignition for at least one hour
• Have a flame spread of no more than 96 inches
• Resist a gas flame that is turned on and off eight times

Class C

Roofing materials rated as Class C offer only light protection from fire. Examples include plywood, particleboard and untreated wood shingles and shakes. These are not recommended as roof coverings. Under testing conditions, Class C roofing materials are able to meet the following requirements.

• Withstand a 1.5-inch by 1.5-inch burning brand that weighs 0.25 gram
• Resist ignition for at least 20 minutes
• Have a flame spread of no more than 13 feet
• Resist a gas flame that is turned on and off three times

Requirements for All of the Classes

Class A, B and C roof coverings must pass all of the following additional tests during a fire or after one.

• Will not fall from or blow off of the deck as glowing or flaming brands
• Will not warp, crack, slide or break to expose the underlying deck
• Will not allow sustained flames on the deck’s underside
• Will not allow glowing particles to fall from the roof deck


Roofing materials that are unable to meet the requirements for even Class C roofs are classified as unrated. Most municipal building codes do not permit unrated roofing materials. Since unrated roofs offer little or no fire resistance, it is highly recommended that they be avoided.

Choose a Knowledgeable Roofing Contractor

Roof fire ratings are not a guarantee that the building or its occupants will suffer no harm during a fire, but higher ratings should allow occupants more time to exit the building if a fire occurs. However, it is important to remember that every component included in a roofing system can impact the building’s roof fire rating. Always choose a knowledgeable, reputable, experienced roofer to ensure that all components meet the standard that you desire.

Alpha Roofing Industries is a roof contractor and we have the expertise to ensure that your roofing system will be correctly chosen and properly installed. We offer an extensive range of services, including the installation of asphalt shingles and metal roofing systems. We also provide roof repairs, skylight installation, flashing repair or replacement, siding installation and many other rooftop services. Our crews are highly regarded and committed to delivering quality results. If you have more questions about Roof Fire Ratings, request a free estimate and complete our online form or call (512) 777-1086.

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