Short answer: nearly every roof leak happens at a penetration or a transition rather than in the middle of a slope. Pipe boots, vents, chimneys, skylights and wall terminations are where the water barrier is interrupted and has to be rebuilt by hand.
Why the field almost never leaks
A field of shingles is a simple shedding surface. Each course overlaps the one below, water runs down and off. There is nothing to go wrong as long as the shingles are intact and sealed.
Every penetration breaks that. The waterproofing has to be interrupted and rebuilt around an object, usually with metal, and that reconstruction is only as good as the person who did it.
The penetrations, ranked by how often they fail
- Plumbing vent pipe boots. The rubber collar degrades under Texas UV at 8 to 12 years. Cheapest item on the roof, most common leak.
- Chimneys. Multiple flashing components plus masonry that moves differently than the roof. See our chimney guide.
- Roof to wall terminations. Needs step flashing woven into each course, plus kick-out flashing at the bottom. The kick-out is the most commonly omitted detail in the whole trade.
- Skylights. Usually the flashing or seal rather than the glass, and frequently because old flashing was reused on a new roof.
- HVAC curbs and mechanical units, particularly on low slope commercial roofs, where service traffic damages the flashing over time.
- Turbine and box vents, where base flashing loosens.
- Satellite and solar mounts installed after the roof, often with sealant instead of proper flashing.
What good penetration flashing looks like
- Metal doing the work, sealant only as a supplement
- Flashing integrated into the shingle courses rather than laid on top
- Ice and water shield around the penetration under the flashing
- New components rather than reused ones
- Counterflashing cut into masonry rather than surface sealed
The sealant test
If you look at a penetration and see a lot of caulk, that is a repair rather than a detail. Sealant has a finite life in Texas sun, usually a few years. A properly flashed penetration does not depend on it.
Why this matters when choosing a contractor
Penetration flashing is slow, fiddly handwork that nobody sees afterward. It is the easiest place to save an hour per penetration, and the consequences arrive years later when the crew is gone.
When comparing quotes, the words to look for are new flashing. If it is not specified, assume reuse.
Get a free inspection with photographs of every penetration on your roof, or call (210) 245-4125.
