Back to Blog Roof Repair Where San Antonio Roofs Leak: The 8 Most Common Sources (And How to Fix Them)
Mark WhiteJuly 1, 20267 min read Here's the thing about roof leaks: the water stain on your ceiling is almost never directly below the actual leak. Water enters the roof at one spot, runs along a rafter or piece of decking, and drips down somewhere completely different. That's why finding a leak is more detective work than construction work.
After thousands of leak investigations in San Antonio, I can tell you that the vast majority come from the same eight places. Here they are, ranked roughly by how often I see them.
1. Pipe Boots (Plumbing Vent Collars)
This is the number one leak source in San Antonio, and it's not even close. Every roof has plumbing vent pipes sticking through it, and each one has a rubber boot that seals the gap between the pipe and the shingles.
That rubber degrades in Texas UV and heat. After 8 to 12 years, the rubber cracks, splits, and pulls away from the pipe. Water runs down the pipe right into your attic. The fix is straightforward: replace the boot. It's a $150 to $300 repair that takes about 30 minutes.
2. Flashing at Wall-to-Roof Transitions
Any place where a roof meets a vertical wall (dormers, second story pop-ups, additions) requires step flashing and counter-flashing. When this flashing corrodes, pulls away, or was improperly installed, water gets behind the wall and into the structure.
I see this most often on homes with additions or bump-outs where the roof replacement meets the existing wall. If the flashing wasn't done right during the addition, it might leak for years before anyone notices.
3. Valleys
Roof valleys are where two roof planes meet at an angle, creating a channel that funnels a huge volume of water. If the valley flashing is damaged, improperly overlapped, or if shingles in the valley are worn thin from concentrated water flow, leaks happen.
In San Antonio's heavy downpours, valley leaks can be dramatic. One hard rain can dump gallons of water into your attic through a compromised valley.
4. Chimney Flashing
Chimneys are notorious leak points because they have four sides of flashing that all need to work together: step flashing on the sides, counter-flashing embedded in the mortar, a cricket (diverter) on the uphill side, and front flashing at the base.
Over time, mortar cracks, caulk fails, and the cricket can deteriorate. If your fireplace has water stains on the wall or ceiling near the chimney, this is almost certainly the culprit.
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Texas temperature swings cause roof decking to expand and contract. Over time, this can push nails up through the shingles, creating tiny holes that let water in. You might see a nail head poking up above the shingle surface.
One or two nail pops is a simple fix. Dozens of them suggest the roof is aging out and the decking movement is widespread.
6. Skylight Seals
Skylights add natural light, but they're a common leak point. The seals around skylights degrade from UV exposure, and the flashing system requires precise installation.
If your skylight is leaking, it's usually the flashing or the seal between the glass and the frame, not the glass itself. Don't just caulk over it. Proper skylight leak repair usually involves reflashing around the unit.
7. Gutter Backup and Ice Dams
When gutter installation are clogged, water backs up under the shingles along the eave. In San Antonio, this usually happens during heavy rains when debris-filled gutters overflow. During rare freeze events, ice can form at the eave and create a dam that forces water upward under the shingles.
The fix is simple: keep your gutters clean. If you're getting backup even with clean gutters, you might need larger gutters or additional downspouts.
8. Worn-Out Shingles
Eventually, the shingles themselves become the leak source. When granules are mostly gone, the asphalt is brittle, and the shingles crack from thermal cycling, water gets through the shingle layer itself.
At this point, spot repairs are just postponing the inevitable. When the shingle material itself is failing, it's replacement time.
Got a roofing question? Something keeping you up at night? (Besides that mysterious dripping sound?) Email me personally at mwhite@legacytx.com. I read and answer every single one.
MW Mark White
Owner, Legacy Home Improvements · San Antonio since 1999
Mark has been in the roofing business for over 25 years. He personally inspects homes, works with insurance adjusters, and answers every email at mwhite@legacytx.com.
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