What is Fire Resistance Rating?

When it comes to protecting your roof, you need to be sure you buy the correct type of roofing materials. As you browse through different selections, you'll notice some standard features listed for each style. These factors describe the material's durability and resistance to issues like wind, impacts, algae, and fire.

Keep reading to find out: What is a fire rating, and why should you care?

Fire Resistance Rating

Manufacturers list their roofing materials in terms of classes from A through C. Some lines are unrated, which means the material did not pass the appropriate testing to receive a classification.

  • Class A - highest rating or fire resistance due to being the least flammable
  • Class B - moderate surface resistance against fires with a flame spread up to 8 feet
  • Class C - minimal fire resistance (not intended for areas with a high risk of fires)
  • Unrated - shingles failed to meet performance requirements to receive a classification (highly unrecommended)

When debating the different materials and fire ratings, be sure to look for options that have a "stand-alone" fire rating as opposed to "by assembly."

A stand-alone rating means the material will have the labeled fire rating without using additional materials. Options with a higher fire rating "by assembly" mean that you'll have to add extra stuff to make the material have a superior fire rating. 

An example would be using a fire-retardant, such as for some aluminum or wood shakes, which gives your roof a Class B rating. There may be the use of Type 72 roll (aka 72-pound cap sheet or 72-pound felt) and DensDeck (panelized gypsum) to increase the rating to Class A.  

Pro Tip: Before choosing a roofing material, it's crucial to check with your local building code. Some states require the highest fire-resistant rating due to the dangers of wildfires.

Fire Rating Tests

The National Fire Protection Association is responsible for assigning fire classifications, using either the UL 790 or the ASTM E108 fire tests.

The materials go through a standard set of fire tests that evaluates the material's performance to determine the fire rating, based on the following criteria:

  • Spread of the flame over the roof surface.
  • Flame penetration that goes through the material and into the attic space.
  • The material's resistance to dislodging and causing embers.

Depending on the type of roofing material, there are 6 possible tests. Burning Brand test, Spread of Flame test, and Intermittent Flame test are the main 3 tests to determine a material's fire resistance. The other three tests occasionally done are the Flying Brand, Rain, and Weathering tests. 

  • Burning Brand Test - A burning brand goes on the roof during strong winds. Monitoring of the roof is done for 90 minutes to check for burn-throughs (the product fails if the fire burns through the roof deck during the observation time)
  • Spread of Flame Test - Air current and flame are applied to the roof together for 10 minutes then the roof is tested for failure
  • Intermittent Flame Test - an intense flame is applied to the roofing assembly for two minutes, followed by two minutes of cooling off. This test repeats 15 times to check for failure of the roof decking

Class A Fire Rating

The roofing material will receive a Class A fire rating if it can do the following:

  • Be resistant to a 12"x12", 2,000-gram burning brand
  • Withstand 15 cycles (on and off) of a gas flame
  • Have a maximum 6-foot flame spread
  • Survive 2 to 4 hours before igniting

Class B Fire Rating

If the roof fails Class A standards but passes the following criteria, it receives a Class B rating. Most Class B products can achieve a Class A rating using complete roof protection. Class B shingles protect against moderate fires with passing scores for:

  • Resistant to 6" x 6", 500-gram burning brand
  • Withstand 8 cycles of flame
  • Survive 8 feet flame spread
  • Lasts an hour before igniting

Class C Fire Rating

Class C fire ratings will provide a minimal amount of protection for your roof, with lower scores for the following factors. Due to the lack of fire resistance, Class C materials are not generally for roofs. 

  • A ¼ gram, 1.5" x 1.5" burning brand
  • With 3 gas flame cycles
  • A 13-foot flame spread
  • 20-minute ignition

When shingles fail to pass one or more of the safety tests, it receives a classification of unrated. These materials will not give you any protection against fire and are not for roofing in any location.

Fire Resistant Ratings by Material

The type of material you choose for your roofing will affect the fire ratings. Some materials are naturally better at resisting fire than others. The chart below outlines the most common types of roofing, along with their fire-resistance rating.

Materials

Fire Rating

Clay

Class A

Concrete

Class A

Slate

Class A

Fiberglass asphalt*

Class A**

Metal

Class A**

Wood shake (untreated)

Unrated

Wood shake (treated)

Class B (Class A with by assembly)

Synthetic

Class A

  • *While asphalt shingles have excellent fire resistance, they are not suitable for locations with the risk of wildfires.
  • **By-assembly fire rating - requires additional materials (insulation, roof deck, underlayment) to become fully Class A rated.

While noncombustible materials like slate, concrete, metal, and clay have high fire resistance, these materials are usually more expensive. Metal is lightweight, allowing for more versatility in architectural styles. In comparison, stone materials are heavier and require additional support to prevent structural issues.

The most common roofing material is fiberglass asphalt shingles, available in 3-tab, architectural, or designer styles. These affordable shingles have a Class A fire rating but usually need extra installation steps to give you the most protection.

In Closing

Where you live will play a significant role in your decision on which fire rating to choose. Most roofing professionals will recommend Class A fire ratings. If you live along the West Coast, where there is a high risk of wildfires, Class A may be a requirement rather than a choice. You can take additional steps to enhance a material's fire rating to Class A, but at additional costs.

Leave a Comment