Roof Flashing Repair
Ask any roofer where leaks start and the answer is flashing, not shingles. Here is why the metal fails while the roof around it stays sound, and how to tell whether it is your problem.
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Flashing causes more leaks than shingles do
Ask any roofer where leaks start and the answer is flashing. Not worn shingles, not storm damage — the thin metal that seals the joins between the roof and everything sticking through or up against it.
The reason is simple physics. Metal and roofing expand and contract at different rates, and Houston puts them through enormous daily temperature swings. Over years that differential movement works the seal loose. The shingles around it can be in perfect condition.
Where flashing lives
| Location | What goes wrong |
|---|---|
| Chimney | The most failure-prone spot on most roofs. Step flashing up the sides, counter-flashing set into the mortar, and a cricket on the uphill side to divert water. Any of the three can fail |
| Walls where a lower roof meets a upper storey | Step flashing woven into each shingle course. If it was face-nailed instead of woven, it will leak |
| Skylights | Four sides, four chances. Usually leaks at the head, uphill side |
| Valleys | All the water from two slopes funnels here. Open metal valley or woven shingle, both fail if debris dams them |
| Drip edge at eaves and rakes | Often omitted entirely on older roofs. Water wicks back under the shingle edge and rots the fascia |
Roofing cement over failed flashing is not a repair. It is the most common thing homeowners find when a previous contractor has been up there, and it buys a season or two before it cracks. Cement is a patch for an emergency, not a fix for a seal.
Chimney flashing, specifically
It deserves its own section because it accounts for so many leaks and because the repair is frequently done wrong.
Proper chimney flashing is two pieces, not one. Step flashing lies under the shingles and turns up against the brick. Counter-flashing is let into a groove cut in the mortar joint and folds down over the step flashing, so water running down the brick is directed out rather than behind.
The wrong version: a single piece of metal caulked against the brick face. It looks fine for a year. Then the caulk fails, water runs down the brick and straight in behind the metal.
How to tell flashing is your problem
- The leak appears near a chimney, wall or skylight — though remember water travels, so "near" means within ten or fifteen feet.
- It leaks in driving rain but not in steady rain. Wind pushes water sideways into a failed vertical seal that gravity alone would not reach.
- Rust streaks on the roof surface below a flashing point.
- Visible caulk or tar at any flashing joint — somebody has already tried to patch it.
- Staining on the chimney breast inside the house, often mistaken for a chimney problem.
Repair or replace the flashing
Flashing can usually be replaced without replacing the roof, and on a roof with years of life left that is exactly what should happen. The job involves lifting the surrounding shingles, fitting new metal properly woven or stepped, and re-laying the shingles over it.
The one time it is not worth it separately: if the roof is within a couple of years of replacement anyway. New flashing is included in any proper replacement quote, so paying for it twice makes no sense. If a contractor recommends replacing flashing on a fifteen-year-old roof, ask what they think the roof itself has left.Call 832-662-4107