CSLB C-39 Roofing ContractorSafety and RepairMedium
A roofing contractor is inspecting a low-slope commercial roof to diagnose a leak. The building owner reports intermittent leaks, primarily during heavy rainfall. The contractor observes several areas where the roof membrane appears to be 'alligatoring' and showing signs of surface erosion, particularly in areas with slight depressions. What is the most likely primary cause of these symptoms?
- AExcessive foot traffic leading to wear and tear.
- BHigh wind uplift causing membrane fatigue.
- CInadequate drainage leading to ponding water.
- DProlonged exposure to ultraviolet (UV) radiation and thermal cycling.
Show answer & explanationAnswer & explanation
Correct answer: C. Inadequate drainage leading to ponding water.
Alligatoring (surface cracking resembling alligator skin) and surface erosion, especially in depressed areas, are classic indicators of prolonged exposure to ponding water. The water accelerates degradation, and the intermittent leaks during heavy rain confirm a drainage issue.
Why the other options are wrong
- A. Excessive foot traffic causes punctures, scuffs, and localized wear, not widespread alligatoring or erosion from ponding.
- B. Wind uplift typically causes membrane billowing, detachment, or tears, not alligatoring or erosion in depressed areas.
- D. UV radiation and thermal cycling cause general aging of the membrane (e.g., cracking, hardening), but when combined with surface erosion and alligatoring in depressions, ponding water is the more specific and primary cause.
Ponding Water Damage
Prolonged ponding water on a low-slope roof accelerates membrane degradation, leading to alligatoring, erosion, and eventual leaks.
- Occurs in areas of inadequate drainage.
- Water acts as a magnifier for UV and thermal stress.
- Shortens roof lifespan significantly.
Memory trick: Ponding water, like a hungry croc, slowly eats the roof, causing leak shock.