CSLB C-39 Roofing ContractorSafety and RepairMedium
A roofing contractor is performing a reroof on a commercial building with a low-slope roof. During the tear-off, the crew discovers widespread delamination and blistering of the existing built-up roofing system. Which of the following conditions is the most likely cause for these specific issues?
- AExcessive foot traffic on the roof surface.
- BInadequate ventilation in the building's attic space.
- CInsufficient drainage causing ponding water.
- DMoisture trapped within the roofing system during installation or from a leak.
Show answer & explanationAnswer & explanation
Correct answer: D. Moisture trapped within the roofing system during installation or from a leak.
Delamination (separation of layers) and blistering (raised areas) in built-up roofing are classic signs of moisture trapped within the roofing plies. This moisture vaporizes when heated, causing pressure that leads to these defects.
Why the other options are wrong
- A. Excessive foot traffic can cause surface wear, punctures, and cracking, but not internal delamination and blistering.
- B. Attic ventilation issues primarily affect the underside of the roof deck or cause ice dams on steep slopes, not delamination within a built-up membrane.
- C. Ponding water primarily causes accelerated degradation and leaks, not typically delamination and blistering from within the system.
Roof Delamination/Blistering Cause
The most common cause of built-up roofing delamination (separation of layers) and blistering (raised areas) is trapped moisture.
- Moisture turns to vapor when heated.
- Vapor pressure causes layers to separate.
- Often due to installation errors or undetected leaks.
Memory trick: Trapped water's steam, a blister's bad dream, makes layers come apart at the seam.