The fire rating of roof coverings is determined for all materials used in code-compliant housing, and will be classified as either Class A, B, C, or 'unrated'. Class A provides the best fire resistance, and therefore for the best protection for your home, you should have a 'Class A' fire-rated roof covering.
At 12 in. by 12-in, the Class A brand is the largest one shown in this photo. The Class B brand is 6 in by 6 in. 'A' and 'B' brands consist of a three layer sandwich construction of 3/4 in. square sticks nailed together, with sticks in the middle later running perpendicular to the outside layers. The Class C brand is about the size of an ice cube.
Burning 'A' brand on a roof deck
Flame-through to the underside of a roof deck. This roof covering failed, and so can't be considered a Class A roof.
Roof coverings can obtain a Class A rating based on the covering alone (called a 'stand-alone Class A') or based on the covering and underlying materials that provide additional fire protection (called an 'assembly-rated Class A'). If you are unsure of the fire rating of your roof covering, the manufacturer of the roof covering can tell you. Often this information will be on the manufacturer's website.
Common 'stand alone' Class A roof coverings include -
2. Clay tiles
3. Concrete tiles
4. Slate
This asphalt composition roof covering is a 'stand alone' A.
Common 'assembly rated' Class A coverings include -
2. Fire-retardant treated wood shakes (with Class B fire rating, approved by the California Office of the State Fire Marshal as a result of passing the required natural weathering test).
3. Some recycled composite materials.
This aluminum roof covering is an 'assembly rated' A. The underlying Type 72 capsheet (roll roofing) material provided additional protections, and is required for the Class A rating.
This fire retardardant treated wood shake roof covering is an 'assembly rated' A. The underlying gypsum panel (DensDeck) material provides additional protections, and is required for the Class A rating. In this case, the fire retardant treated shake is a 'stand alone' Class B covering.
It can be difficult to determine if the fire rating of a given product has a 'stand alone' or 'assembly' rating, since a published 'Class A' rating could refer to either. If you aren't sure, get a copy of the installation instructions for the roofing materials. If the installation instructions call for Dens-Deck or Type 72 capsheet material, in addition to Type 15 or 30 roofing felt and other structural sheathing (plywood or oriented strand board), you have an 'assembly rated' Class A covering.