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Understanding Roofing Fire Ratings: How Fire-Resistant Is Your Roof?

By Kravelv @kravelv

A fire-resistant roofing system should be able to resist fires coming from both inside and outside the building.Is your roof up to the fire test? Find out how well your roof will able to stand against varying degrees of heat and flame by understanding the different ratings.

External Fire Exposure

Roof performance against external fire sources, such as wildfires or compromised roof equipment, is measured through the ASTM E108 test. This test measures the response of materials, products, or assemblies by exposing them to simulated heat and flame in controlled laboratory conditions. Different types of buildings require different fire ratings, which depend on building location as well. The Class A, B, or C ratings that are given are actually results from the three different tests conducted for each category.

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  • Class A Tests, required for high-risk buildings such as theaters, hospitals and schools, apply to roof coverings effective against severe test exposure. Roofing systems that undergo and pass this test afford the highest degrees of fire protection to the roofing system from external sources. Common Class A roof materials include asphalt fiberglass composition shingles, concrete or clay tiles, gravel-surfaced built-up roofing, and single-ply systems.
  • Class B Tests apply for roof coverings that are measured against moderate test exposure, and therefore should provide fire protection to a moderate degree. Mineral-surfaced roofing systems usually meet the Class B requirement.
  • Class C Tests are applicable to roof coverings exposed to a test with light heat and flame exposure. Roofing systems that pass this test afford a lighter degree of fire protection compared to Classes A & B, but still meet the requirements for less critical buildings or structures.

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Additional tests such as the burning brand and intermittent flame tests are required for more combustible roofing materials, such as wood and plywood.

Roofing systems can achieve the requirements for these tests through the proper assembly of  prepared roof-covering materials or roofing systems. Roof-covering materials such as asphalt or glass-fiber shingles are installed on combustible roof surfaces to improve fire resistance. Roofing systems, on the other hand, consists of a combination of materials that can be installed on both combustible or noncombustible roof surfaces. These materials include  metal panels, hot asphalt or coal tar felt, fluid-applied coatings, single-ply membrane, spray-applied foam and coating, and photovoltaic modules. These should be installed by a professional roofing contractor as improper usage or installation can damage your roof and decrease its durability.

Internal Fire Exposure

Fires can originate from the interior of the building or structure as well the outside. In these instances, preventing the further spread of the fire depends on the fire-resistance of the exposed surfaces like the walls and ceiling.

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The Steiner Tunnel or ASTM E84 test observes and measures the flame spread and smoke generation of the roofing material. It is a requirement for many commercial building materials. Through the use of a vented tunnel lined with firebrick and equipped two gas burners, the test material is mounted on top of the chamber and subjected to a high-energy flame for ten minutes. Flame spread across the material is observed through windows built into the tunnel while an optical cell mounted at the tunnel exhaust is used to measure smoke density. A flame spread index and a smoke-developed index are then calculated from the results.

With asbestos-cement board having a value of 0, and red oak wood a value of 100, U.S. building codes require certain roofing materials to have a flame spread index of 0-25 and a smoke developed index of 0-50 when tested.

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Author Bio:

Jon Fleming, along with brother Don, is a second generation family business owner of Vinylume Home Improvement. Upon graduation from college, Jon worked eight years as a reporter in New York City and Albany, NY, before rejoining the company. Today Jon is vice president of sales and marketing.Sources:

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