What is a common failure mode in Built-Up Roofing (BUR)?

• A. Moisture intrusion at flashings
• B. Poor seam bonding
• C. UV degradation of membrane
• D. Trapped air causing blisters

Answer: (A)

Moisture intrusion at flashings is the most common failure path for Built-Up Roofing because flashings are the critical transition points where the horizontal roof surface meets vertical or complex edges. These details are where water is most likely to find a path into the roof system, especially when flashing installation is imperfect, the substrate moves with temperature and load, or penetrations and terminations are not properly integrated with the membrane. When water sneaks behind flashings, it can travel into the insulation, deck, and even structural members, causing rot and deteriorating adhesion of the asphalt and felt layers. The BUR layers themselves shed water, but if the flashing detail is compromised, the leak bypasses the protective layers and becomes a frequent, persistent problem. Other issues like UV degradation, trapped air causing blisters, or poor seam bonding can occur, but the likelihood of leaks driven by flashing details makes moisture intrusion at flashings the most common failure mode.