Why Roof Penetrations Leak in South-Central Texas
Every roof penetration—whether a 3-inch PVC plumbing vent or a 4x4-foot skylight—interrupts the continuous shedding plane of your roof. In San Antonio's harsh climate, these intersections face intense localized stresses:
Plumbing Pipe Boots (Collars)
Standard builder-grade pipe jacks use a thin neoprene rubber gasket molded to an aluminum or plastic flange. Under San Antonio's intense UV radiation and 150°F+ attic heat, the rubber loses elasticity in 5 to 7 years. It develops radial cracks around the pipe circumference. Rain running down the exterior of the pipe stack flows straight into attic insulation.
Proper Fix: Installing heavy-duty silicone or lead pipe collars rather than relying on caulk that shrinks away in summer heat.
Skylight Flashings vs. Glazing Seals
Skylight leaks require diagnosing the exact point of entry:
- Curb Flashing Failure: Step flashing and saddle flashing around the raised wooden curb detach or rust, letting water enter behind interior drywall shafts.
- Glazing Gasket Failure: Synthetic seals between glass panes dry out, allowing condensation and driving rain between panes.
- Hail Impact: Large hailstones shatter polycarbonate domes or crack tempered glass outer panes.
Symptom Differentiation: Interior Condensation vs. Exterior Breach
During humid winter cold snaps in San Antonio, warm interior air can condense on cold single-pane skylight glass, creating dripping that mimics a roof leak. An independent roofing contractor can evaluate whether stains stem from inadequate thermal insulation/ventilation or an active exterior flashing breach.