Underlayment is a good example of a material that operates behind the scenes to support the roofing system. Simply defined, roofing underlayment acts as a water-and-vapor-resistant material located below the top roofing layer. Installed directly on the roof deck, underlayment protects against moisture infiltration and provides a secondary water shedding barrier. Additionally, underlayment can be critical for a roof's fire resistance. Most roof coverings cannot achieve a Class A fire resistance classification without the inclusion of underlayment in the roof assembly. Without the protection of an underlayment layer, a home's roof deck is more exposed and subject to water and fire damage.
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