Dunn Contracting installs a secondary water barrier with every new roof.
Premium underlayments are not meant for use as a primary roof. The combination of direct sunlight, ultraviolet radiation and rain or snow would alternately oxidize and wash away the asphalt-rubber blend and the membrane, causing it to fail. Underlayments protect the building from water damage when the primary roof leaks. Usually, even damaged primary roofs continue to protect the underlayment from physical harm and UV rays, so underlayments can be highly effective as a last line of defense until there is an opportunity to make repairs.
Since their introduction into the residential roofing marketplace just a few years ago, premium self-adhering underlayments made of SBS-modified asphalt have been broadly adopted, applauded and accepted by roofing contractors. As a result, most contractors now are familiar with various types of self-adhering underlayments and their installation, especially with regard to their use under asphalt shingles.