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July 19th, 2010 admin Leave a comment Go to comments

Airborne Tab

Three Factors that Architects, Builders and Property Owners Must Address Before they Choose a Roof

Fire Safety and Protection

Fire safety is a particularly important consideration, since the roof is vulnerable to fire from overhead or airborne sources.The fire resistance of roofing materials is tested by the Underwriters’Laboratories, Inc. (UL), an independent, not-for-profit public safety testing laboratory. UL established the standard for the testing of roofing materials with the assistance of nationally recognized fireauthorities.

Manufacturers voluntarily submit materials for testing. The materialsthen are classified and labeled according to the classes below. The American Society for Testing and Materials (ASTM) is a voluntary organization concerned with the development of consensus standards,testing procedures, and specifications.

Class A. The highest fire-resistance rating for roofing as per ASTM E-108. This class rating indicates that the roofing material is able to withstand severe exposure to fire that originates from sources outside the building.

Class B. This fire-resistance rating indicates that the roofing material is able to withstand moderate exposure to fire that originates from sources outside the building.

Class C. This fire-resistance rating indicates that the roofing material is able to withstand light exposure to fire that originates from sources outside the building.

Many communities require new roof coverings to meet at least theUL Class C standard. This requirement has the backing of nationally recognized authorities such as the National Fire Protection Association and the International Association of Fire Chiefs. Some roofing materials, such as slate and clay tile, offer natural fire protection. Asphalt shingles are manufactured to meet the Class C standard or better. Readily combustible materials, such as wooden shingles, do not meet the UL standard unless they have been chemically treated for fire retardancy.

Wind Resistance

UL also tests shingle performance against high winds. To qualify for the UL wind-resistant label, shingles must withstand continuous test winds of at least 60 miles per hour for two hours without a shingle tab lifting. Wind-resistant shingles demonstrated their effectiveness under hurricane conditions during the winds brought to Florida in 1992 by Hurricane Andrew, which at the time was the worst hurricane ever recorded in the United States.

Self-sealing asphalt shingles that bear the UL wind-resistant label are manufactured with a factory-applied adhesive. Once the shingles are applied, the sun activates the preapplied thermoplastic sealant and each shingle is bonded to the one below it. Although self-sealers originally were developed specifically for high-wind areas, they are standard in most parts of the country today.

Estimating Life Expectancy

In addition to fire and wind ratings, roof coverings have a life expectancy. Manufacturers offer a guarantee or warranty for their products. For example, most of today’s asphalt shingles are designed to provide satisfactory service for 15 to 25 years.

Generally, the longer the life expectancy, the more expensive the shingle material. You might find, however, that a more expensive shingle is the most economical in the long run because the cost of materials and labor is amortized over a longer period of time. Keep in mind that while the labor cost to apply the shingles varies with the product, it is the same whether the life expectancy of the shingle is 15 or 25 years.

Estimate the probable annual cost of a new roof by adding the cost of labor and materials and then dividing the total by the shingle’s design life. The formula for determining the annual cost of use is

Total cost (material and labor)/design life=annual cost of use

About the Author

FG is the rapporteur of the Search Construction Schools Website http://www.search-constructionschools.com/