Three Fire-Retardant Classes Used to Rate Roofing Material in St. Charles

Underwriters Laboratories, Inc (UL) is the most well-known independent safety certification company. They use three classes to rate how fire-retardant roofing materials are. Residential roof contractors in St. Charles, MO, uses these categories also.

These classes are:

Class A – Least Flammable

  • Maximum flame spread of six feet
  • Withstand up to a 12′ x 12′ burning brand weighing up to 2kg
  • Two to four hour ignition time
  • Resists 15 cycles gas flame cycles

Asphalt with fiberglass underlay, clay, and slate are examples of Class A roofing materials.

Class B – Semi-Flammable

  • Maximum flame spread of eight feet
  • Withstand up to a 6′ x 6′ brand up to 500 grams.
  • One-hour ignition time
  • Resists eight cycles gas flame cycles

Shakes and shingles fall under the class B category.

Class C – Barely Fire-Retardant

  • Maximum flame spread of 13 feet
  • Withstand a 1.5″ x 1.5″ brand up to 1/4 of a gram
  • Twenty-minute ignition time
  • Resists three gas flame cycles

Untreated shakes, shingles, and plywood all fall under this category.

If a roof material isn’t rated, you may as well be using paper.


Now that you know about the different classes to rate how fire-retardant certain roofing materials are, you can make more informed decisions. Affordable Exteriors are a premier residential roof contractor in St. Charles, MO, with the best roof material options.

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