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Rockville Roofing: Article About Impact Resistant Roofing Ratings

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Hail is the leading cause of impact damage to roofing materials. When shopping for a new roof, homeowners are will notice that impact resistant materials come with a rating from 1 to 4. Any Rockville roofing contractor knows that 4 is the best and 1 is the lowest rating. For homeowners who wonder how the ratings are decided, here is a little background.

In 1996 Underwriters Laboratory (UL) developed the UL 2218 Impact Resistance of Prepared Roof Covering Materials standard fare followed by the UL 4473 standard for rigid tile roofing. These four point scales are designed to give homeowners and contractors a good idea of how well different roofing options withstand hail damage. Insurance companies also use these ratings to determine the likely rate of failure. Selecting a roofing material with a higher rating can lower insurance premiums in some locations.

The testing for UL 2218 is conducted by dropping a solid steel ball on to the material in the same place twice. The size of the ball used gets bigger with each successive level, and the height of the drop is also increased. To pass each level, the material must show no damage on the exposed layer, under layer or bottom surface.

A roofing expert from Seneca Creek Home Improvement of Rockville MD would be happy to answer any question you have about windows or doors.

The damage tested for includes cracking, splitting, tearing, fracturing, rupture or any condition that would leave the decking exposed to weather damage.

The UL 4473 test for roofing tiles is rated on the same four point scale. The difference is that ice balls are fired at the tiles at speeds that simulate falling hail.

Some roofing materials are naturally more resistant to impact damage. Rubber and plastic tiles, for example, absorb shock better than clay tiles. The type of damage each material is prone to also varies. Asphalt shingles will split or crack while metal roofing dents. Each type of failure can lead to eventual weather damage to the underlying structure.

Different aspects of a material can be changed to increase its impact resistance. Wood, for example, must be made thicker or denser to help it resist splitting. Likewise, thicker or harder metal does not dent as easily. Asphalt and composite materials must have their composition adjusted to increase flexibility. Plastic and rubber roofing materials are usually designed to score a 3 or 4 because of their natural flexibility. The shape and thickness of rigid roofing tiles affect their resistance to cracking and fracturing.

Most roofing professionals will recommend installing a material with at least a 3 rating. However, in areas where hail is a common occurrence, it is best to stick with products rated 4.

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