What causes blisters in built-up roofing?

Blisters in built-up roofing are primarily caused by water or air expanding below the roofing materials. When moisture gets trapped beneath the roofing layers during installation or due to leaks, it can turn into vapor as temperatures rise. This vapor exerts pressure, causing the layers of the roofing to lift and form blisters on the surface.

Additionally, if there are pockets of air trapped during the roofing process, these can also expand with heat, contributing to the formation of blisters. Blisters are a significant concern because they can lead to further damage by allowing water to infiltrate and potentially compromise the structural integrity of the roofing system. Understanding this mechanism is crucial for proper installation and maintenance of built-up roofing to avoid costly repairs and prolong the lifespan of the roof.