Chimney Flashing Repair in San Antonio: Costs and Fixes

Water stains on the ceiling near a fireplace almost always trace back to one thing, and it isn’t the shingles. Chimney flashing repair is one of the most common fixes we make on local roofs, because the joint where a chimney passes through the roof is the hardest part of the whole system to keep watertight.

That joint moves. The chimney is masonry sitting on its own footing. The roof deck is wood that expands and contracts with heat. Those two things shift at different rates, all year, and the only thing bridging them is a few pieces of bent metal and some sealant.

Here’s what makes it frustrating for homeowners: the leak shows up in the living room, months after the flashing actually failed. By then the water has been running down a rafter and soaking decking you can’t see.

This walks through what chimney flashing is, what a repair really costs, when resealing is enough and when it isn’t, and one warranty detail that catches almost everybody off guard.

What is chimney flashing, and why does it fail first?

Chimney flashing is the metal that seals the joint where the chimney passes through the roof. It’s not one piece. A proper installation uses base flashing at the bottom, step flashing woven up both sides, and counter flashing set into the masonry above it. It fails first because that joint moves constantly while the rest of the roof sits still.

Think of it as three layers doing three different jobs. Base flashing handles the uphill and downhill sides. Step flashing runs up the slopes in overlapping L shaped pieces, one per shingle course. Counter flashing tucks into the brick and laps over the top of everything else, so water hitting the chimney gets shed outward instead of running behind the metal.

GAF’s technical guidance is specific about this. Their bulletin on proper flashing says step flashing must be covered with an appropriate counterflashing, must be non corroding metal, and must be sized to the shingle. For a shingle with a 5 inch exposure, that means a 5 by 5 by 7 inch piece. The same bulletin warns that plain L metal shouldn’t be used at these transitions at all, because it’s prone to leaking.

That’s the part cheap repairs get wrong. Somebody runs a bead of caulk along the brick and calls it sealed. Caulk is not flashing. It buys a season.

How much does chimney flashing repair cost?

Expect roughly $150 to $500 for a reseal and $400 to $1,600 for a full flashing replacement. Those are the figures local and national providers currently publish, not BH Roofing quotes. Cost depends on chimney size, how many sides need step flashing, whether the counter flashing has to be cut back into mortar, and whether water already reached the decking underneath.

Two published sources bracket the range. Angi puts chimney flashing repair at $400 to $1,600, with resealing minor leaks starting around $200. Locally, chimneysweep-sanantonio.us publishes $150 to $500 for repair and $400 to $1,600 for replacement.

We don’t publish a flat rate, and you should be a little suspicious of anyone who does before looking at your roof. The single biggest cost variable isn’t the flashing at all. It’s what’s under it.

If a leak has been running for a while, budget for decking. On the job we describe below, the deck had to be opened up before any flashing went back on.

Should you reseal the flashing or replace it?

Reseal only when the metal is genuinely sound, meaning no rust, no bends, no torn nail holes, and it’s sitting flat. Replace it in every other case. GAF’s position is that reused flashing should be in like new condition, and that all metal flashings should be replaced whenever possible. Old metal with existing holes gives water a path no sealant closes.

This is where homeowners get talked into the wrong fix. Resealing is cheaper today and it’s the right call sometimes. But the GAF bulletin on reusing metal flashings sets a real bar: the metal has to show no signs of excessive wear, damage, corrosion, rust, scoring or tearing, and its remaining service life needs to match the life of the new shingles.

Most flashing that’s leaking doesn’t clear that bar. If it’s old enough to leak, it’s usually old enough to replace.

Reusing old flashing is one of the most common reasons a repair doesn’t hold, which we cover in more depth in our guide on why a roof still leaks after a repair.

What a proper chimney flashing repair involves

The short version: open it up, fix what’s underneath, install new metal in the right order, then seal.

Here’s a real example. On a roof repair we completed in 78248, the crew took the affected area down to the deck rather than patching over it. Damaged and rotted decking came out first. Then new base flashing went in, with surface mounted counter flashing over it, continuous flashing run across the area for a uniform finish, and roof to wall saw cut flashing installed where the roof met the wall. The area was resealed and re shingled with Owens Corning Duration shingles in Driftwood so the repair blended into the existing roof. Final inspection confirmed the installation was correct and code compliant.

That sequence matters more than the materials. Flashing works by lapping, not by sticking. Each piece has to shed water onto the piece below it. Install them out of order, or rely on sealant to close a gap that should have been lapped, and it leaks again in a year no matter how good the metal is.

Notice the part most homeowners never see: the decking came out first. If the deck under the flashing is soft, new metal on top of it is decoration.

One more piece worth asking about on a wide chimney: a cricket. That’s a small peaked structure built behind the chimney that splits water and sends it down both sides instead of letting it pool against the brick. It isn’t optional on every home. The International Building Code requires a cricket when a chimney built after 2012 measures more than 30 inches wide. Older chimneys are generally grandfathered in, which is why plenty of wide chimneys around here don’t have one and collect water behind them every storm.

The warranty detail almost nobody knows

Your shingle warranty probably doesn’t cover your flashing.

GAF states it plainly in the same proper flashing bulletin: flashings are not covered under the manufacturer’s limited material warranty. So a homeowner with a strong shingle warranty can still be fully exposed on the exact component most likely to leak.

It goes one step further. GAF’s bulletin on reused flashings answers the question of whether reusing existing metal voids the shingle limited warranty with a straight yes, in some cases.

One important nuance, because the tier changes the answer. That exclusion applies to the manufacturer’s material warranty. GAF’s enhanced tiers work differently: Golden Pledge and Silver Pledge misapplication coverage explicitly includes flashings at valleys, dormers, chimneys, and plumbing vents, which GAF calls Covered Flashings. So whether your flashing is covered comes down to which warranty you actually hold. We break the tiers down in our guide to what a roofing warranty actually covers.

Put those together and you get a situation worth understanding before you approve a cheap repair. A contractor who reuses questionable flashing to keep the price down may be handing you a leak and a warranty problem at the same time. As a GAF Master Elite contractor, we install new flashing on repairs and replacements as standard practice, and that’s why.

Why chimney flashing fails faster on local roofs

Our climate goes after flashing specifically. Heat and UV bake the sealant around the metal until it cracks and pulls away, and that happens years before the shingles look worn. On leak calls the culprit is often a small failed component rather than the roof itself, a dried out pipe boot or a lifted piece of flashing.

The heat cycling is the real mechanism. Metal expands and contracts every single day here, more than it does in a milder climate, and it does that against masonry that barely moves at all. Sealant is what absorbs that difference. Sealant is also the first thing our sun destroys.

Then spring arrives. Heavy oak pollen and leaf drop pack gutters and valleys right as storm season starts, so water backs up onto the roof instead of draining. Water that sits, finds every edge that’s already worn.

That combination is why a roof here can look completely fine from the street and still be one hard rain away from a stain on the ceiling. The sun does the quiet damage for months. The storm just finds it. Our guide to preventing roof leaks covers the maintenance rhythm that stays ahead of it.

Roofer or chimney sweep: who should do this work?

Call a roofer when the leak is at the flashing, meaning the joint between the chimney and the roof. Call a chimney sweep for the flue, the cap, the crown, and anything inside the chimney itself. Flashing is roofing work, because fixing it correctly means lifting shingles, checking the decking, and reinstalling the roof system around the chimney.

It’s a fair question, and search results genuinely blur it. Right now the top result for chimney flashing repair in our area is a chimney sweep company, not a roofer. They do good work on chimneys. But flashing repair done properly involves the roof deck and the shingle courses, and that’s a different trade.

The practical test: if water is coming in where the chimney meets the roof, it’s flashing, and it’s roofing. If smoke is backing up or the crown is cracked, that’s the sweep’s job.

Either way, get the actual source found before anyone starts. Water travels along the deck before it drips, so the stain inside is rarely under the entry point. Our guide on how to detect roof leaks in the attic walks through tracing it properly.

What to do next

Three things worth remembering. Chimney flashing repair costs roughly $150 to $500 for a reseal and $400 to $1,600 for a replacement based on published local and national figures, and the decking underneath is the variable that moves the number most. Reseal only if the metal is genuinely sound, because GAF’s own bar for reusing flashing is like new condition. And know that flashing sits outside your shingle material warranty, which makes doing it right the first time worth more than saving a hundred dollars today.

If there’s a stain near your fireplace, don’t wait for the next storm to tell you how bad it is. Our free 27-point roof inspection includes photos and a written report, and it’ll tell you whether you’re looking at a reseal, a replacement, or decking work underneath. Call (210) 267-9029 or schedule a roof repair inspection.