What does the presence of blisters and bubbles on a built-up roof indicate?

The presence of blisters and bubbles on a built-up roof is an indication of moisture trapped between the felt-plies. This occurs when water or humidity becomes trapped within the layers of roofing materials, causing the layers to separate and create pockets of air or water. These blisters can develop due to high temperatures, which causes the trapped moisture to expand, leading to the formation of bubbles or blisters on the roof's surface.

Identifying this issue is crucial, as allowing moisture to remain trapped can lead to further deterioration of the roofing system and potential leaks. Timely intervention can help mitigate damage and extend the longevity of the roof. Understanding this phenomenon is essential for anyone involved in roofing inspections or maintenance planning.