The roofing material you use is a major factor in stopping the spread of flames. State laws have improved the fire safety requirements for homes, and replacing old roofs with fire-resistant materials has become a normal part of renovating older homes.
Roofing materials are rated for fire safety using letter grades. Like school grades, A is best, followed by B and C. There is an unrated rating, too, for materials that are not fire-resistant at all. However, choosing based on rating is not that simple. Sometimes you have to combine materials to get your desired rating.
Stand Alone vs. Assembly Rated
Class A is the class you should always aim for when choosing roofing materials. Sometimes the roofing material itself is rated as Class A; this is known as stand-alone Class A material. Another type of Class A roof is an assembly-rated roof, in which a combination of materials form a roof with a Class A rating even if the materials themselves are not Class A on their own.
For example, wood shingles treated with a fire retardant chemical may be Class B on their own, but if you install an additional fire-resistant barrier with the shingles, the whole roof may be rated as Class A.
Preference, Cost, and Time Available
It doesn't really matter whether you choose stand alone or assembly-rated roofing as long as your finished roof meets Class A standards because there's no sense in constructing a roof that meets only Class B or Class C standards.
Keep in mind, though, that the more material you have to install, the more you'll pay, and the longer it will take to finish the roof. Another issue to consider is that certain materials have additional effects on the comfort of the home.
For example, half-moon-shaped clay tiles can have a cooling effect on a home because the space under the tiles allows breezes to blow hot air away from the roof. If you're in a hotter part of the Bay Area, then, you may want to favor clay tiles over other types of roofing materials.
Still, looks count for a lot. If the home you're working on is in an area where the dominant style is wood-style shingles, then using treated shingles and a fire-resistant barrier is just fine.
Don't Forget Landscaping and the Eaves
No doubt you've encountered homes where tree branches overhang the roof and where unkempt yards encourage tall grasses to hug the perimeter of the house. As you install the new roof, point out the landscaping problems to the company that's arranging for the renovation.
Homeowners, be they individuals or a company that plans to rent out the house, should create defensible space around the property, even if the property is in the middle of an urban area. Messy, dead plant life only increases the chances of a fire spreading to the home.
Part of the fire safety of a roof also lies in what's under the roof as well. Vents, soffits, and eaves often aren't included when someone quickly calculates what materials might be needed for a fire-resistant roof. If you are buying materials for roofs, then also look at ignition-resistant materials for soffits, vents and eaves, all of which can trap embers and allow flames to bypass the top surface of the roof.
For more in-depth discussion of fire-resistant roofing materials, contact Al's Roofing Supply. It's imperative that the roofs you construct meet the most stringent fire-safety standards possible.