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Posted by Caryn Colgan | Feb 24, 2010

Comparing Roofs' Fire Resistance

Wood roofing is the most flammable, while metal, slate and concrete will withstand a blaze the longest.

Building codes in fire-prone areas often require fireproof or fire-resistant materials to be used on the roof. A building's roof is the most vulnerable part of a structure, since embers can be blown onto the roof well before a fire reaches the immediate area. A fire-resistant or fireproof roof gives the structure a better chance to survive a fire.

Shingles are categorized into classes that identify their fire resistance. Class A roofing materials are the most fire-resistant; classes B and C denote progressively less fire-resistant qualities. Generally, most fiberglass shingles have Class A fire ratings, and most organic shingles, such as treated wood shingles, have class C ratings.

Asphalt Shingles

Class A asphalt shingles can withstand a fire burning through the wooden structural components for up to two hours. Because asphalt shingles are relatively inexpensive, they are the most common roofing material, especially in areas where fire isn't an ever-present danger. In fire-prone areas, other fireproof or fire-resistant materials are superior to asphalt shingles.

Concrete and Clay

Concrete is used more often in industrial and commercial construction rather than residential. For residential buildings, concrete or clay tiles are fireproof, durable roofing materials. Often used for Spanish, Southwest and Mission architecture, the concrete or clay rounded tiles are heavy and require additional structural support.

Slate

Slate is another heavy roofing material that offers the advantage of not burning. While it is nearly indestructible, it tends to be expensive and requires skilled contractors to install it. Due to the weight of slate, a qualified contractor or engineer will need to evaluate the load-bearing capability of the existing structure. Additional support beams or braces may need to be installed to support the weight of this beautiful and fireproof material.

Metal

Metal roofing is available in zinc, copper, steel, stainless steel and other alloys. Particularly useful in salty coastal areas, most metals are non-corrosive and will resist burning. Metal roofs are also suitable for roofs with a steep slope where heavy materials such as slate and tile are impractical or dangerous. Metal sheets and shingles can also be fashioned to resemble cedar shake and other roofing materials, but without the fire hazard. Consider metal rooftop coatings and insulation. Kymax Metal Roof Top Coating is algae, mildew and fire-resistant.

Some builders add products such as Kynar. This insulating metal roof product is fire, corrosion, abrasion, moisture and UV-resistant.

Other Considerations

According to the National Roofing Contractors Association, homeowners should keep tree branches trimmed and away from the roof. Not only do branches scratch and damage roofing materials, if they catch fire, they can ignite the nearby house.

Anyone interested in learning more about fire safety, codes and other important fire-related information can visit the National Fire Protection Association.

Since the roof is a structure's most vulnerable area, a fireproof or fire-resistant roof is particularly important in areas prone to fires. By carefully choosing the roofing materials, property owners can prevent wind-borne embers from damaging or destroying the property.

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