Advantages – Because the system is multi layer it has greater puncture resistance, and the redundancy provides more protection against roof leaks. Asphalt works well as both an adhesive to hold the felts together and to the substrate and as a water resisting material to prevent moisture penetration.
Disadvantages – Installation errors are often hidden because of the redundancy and can result in premature failure. Due to the increased cost of oil, asphalt built up roofs have become the most expensive roofing system to install. Asphalt is adversely affected by ultra violet rays and will not maintain it’s integrity in ponding water situations because it is moisture resistant rather than moisture proof.