The cracking of the surfacing bitumen on a built-up roof, produces a pattern of cracks, similar to an alligator's hide. Cracks can develop down to the depth of the felts and may stress-crack the membrane in cold weather. The channels that form as a result of the cracking can hold water which penetrate the membrane.
Blistering
Blisters are enclosed pockets of air mixed with water vapor, trapped between impermeable layers of felt or the roof membrane and substrate. Blisters can be broken by foot traffic or hail, which results in punctures to the membrane. Blisters may also affect drainage and become so large that they pull seams apart.
Deterioration of Base Flashing
Loss of the protective coating on base flashing can result in holes and tears.
Ponding
Before and After Drain Installation
Loss of the protective coating on base flashing can result in holes and tears.
Obstructed Drainage
Obstructed Trough (Before & After)
Obstructed Scupper (Before & After)
Leaks can occur when drainage systems are not kept free of debris. Obstructions can cause water to back-up through masonry walls, and to travel in areas it normally wouldn't reach.
Heavy Snow Fall
Severe weather conditions can cause special problems. Accumulated snow can backup into roof vents. The snow then melts and causes interior water damage. Snow and ice need to be cleared from around roof vents.
