NASCLA Accredited Commercial General ContractorThermal and Moisture ProtectionEasy
During a commercial building inspection, a contractor observes dark, moist stains on the interior ceiling of the top floor, directly below a parapet wall. There are no visible cracks in the parapet's coping. Which of the following is the most likely cause of this water intrusion?
- AInadequate flashing or sealant failure at the parapet wall/roof intersection
- BPlumbing leak from an upper-level fixture
- CFailure of the roof membrane at the field of the roof
- DInsufficient attic ventilation leading to condensation
Show answer & explanationAnswer & explanation
Correct answer: A. Inadequate flashing or sealant failure at the parapet wall/roof intersection
Water stains below a parapet wall, especially without visible coping damage, strongly suggest a failure in the flashing or sealant where the roof membrane meets the vertical parapet wall, allowing water to penetrate.
Why the other options are wrong
- B. A plumbing leak would usually be associated with a water supply or drain line, not typically localized at a parapet wall unless a pipe was embedded there.
- C. A field membrane failure would likely show signs of water intrusion in the middle of the roof area, not specifically at the parapet.
- D. Condensation typically presents differently, often as widespread moisture or mold, not localized stains directly below a parapet.
Parapet Flashing Failure
A common source of roof leaks where the flashing or sealant at the intersection of a roof membrane and a parapet wall degrades or detaches, allowing water to penetrate.
- Often manifests as interior stains below the parapet.
- Can occur even if coping is intact.
- Critical detail for roof waterproofing.
- Requires proper detailing and material compatibility.
Memory trick: When water drips, check the 'Edges and Penetrations' first.