Your roof can have one of four fire ratings classifications: Class A, Class B, Class C, or unrated. A Class A roof is ideal for fire protection and may be required by your building codes depending on your place of residence. Whether you’re constructing a new home or outfitting an addition, it’s important to understand and carefully consider the fire rating as you’re choosing roofing materials.
Understanding Roof Fire Ratings
Class A Roofing
Class A roofing is the preferred choice for any home, but this type of roofing is particularly important if you live in an area that is prone to wildfires. To achieve a Class A rating, the roof must be effective against severe fire exposure. This is proven if it can:
- Experience maximum flame spread of 6 feet
- Withstand a burning brand measuring 12″ x 12″ and weighing 2,000 grams
- Last 2 to 4 hours before ignition
- Resist 15 cycles of a gas flame turned on and off
Common stand-alone Class A roof coverings include clay tiles, slate, asphalt glass fiber composition shingles, and concrete tiles. Assembly-rated Class A roof coverings are those that meet Class A standards when combined with other elements. For example, shake roofing with a fire-retardant treatment rates Class B on its own, but achieves a Class A rating when combined with specified underlying materials such as Type 72 roll roofing material.
If you use an assembly-rated roofing material, it’s crucial that you read the manufacturer’s specifications carefully. These will detail exactly which materials to combine for your roof to achieve a Class A rating.
Class B Roofing
Class B roofing is effective against moderate fire exposures. This is proven when the roofing can:
- Experience maximum flame spread of 8 feet
- Withstand a burning brand measuring 6″ by 6″ and weighing 500 grams
- Last 1 hour before ignition
- Resist eight cycles of a gas flame turned on and off
Pressure-treated shakes and shingles are the most common roofing materials to fall under the Class B rating.
Class C Roofing
Class C roofing provides only light fire protection. Roofing with a Class C rating is able to:
- Experience maximum flame spread of 13 feet
- Withstand a burning brand measuring 1.5″ x 1.5″ and weighing 1/4 gram
- Last 20 minutes before ignition
- Resist three cycles of a gas flame turned on and off
Examples of common Class C building materials include untreated wood shakes and shingles, plywood, and particleboard. This is not a recommended roof covering.
If roofing is unrated, this means it could not pass even the requirements for Class C roofing materials. This type of roofing provides little, if any, fire resistance and should be avoided. Most building codes will not accommodate any type of unrated roofing material.
Understanding the fire rating for your roofing materials will help you determine how safe your home is in the event of a fire. Depending on the requirements of your area’s building code, these ratings may also determine whether a particular roofing material is even a viable option. With the right roofing, you can enjoy a durable construction that’s both beautiful and safe.