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GAF Flashing Replacement: The San Antonio Owner’s Guide
GAF flashing replacement in San Antonio typically runs $350 to $900 installed for a single penetration point like a chimney, vent pipe, or skylight, depending on access and how much surrounding shingle work is involved. Most flashing failures on GAF roof systems in our area get caught after heavy rain, when water finds its way inside. We keep GAF-compatible flashing stock on hand and can often complete the swap the same visit once we’ve matched the part to your roof’s specific layout. You’ll likely notice it the way most San Antonio homeowners do: a brown stain on the ceiling below a chimney or a drip that only shows up during a driving south Texas downpour.
Flashing is the metal that seals the joints where your roof meets anything vertical, like a chimney, wall, or pipe boot. When it fails, the roof itself can be in perfect shape and water still gets in. That’s the frustrating part, and it’s the number one reason we get calls for what looks like a roof leak that turns out to be a flashing problem instead.
Which GAF Models This Applies To
GAF doesn’t make flashing under a single model number the way they do shingle lines like Timberline HDZ or Royal Sovereign. Flashing is fabricated to match the roof’s pitch, the penetration type, and the surrounding material. What matters for compatibility is matching the flashing profile and gauge to your existing GAF system so the seal stays tight and the install looks intentional, not patched.
We work with GAF-compatible flashing across the Timberline, Royal Sovereign, and Glenwood shingle lines, plus GAF’s low-slope systems like Liberty SBS. The key identification step is measuring the penetration and checking the existing step flashing depth. In San Antonio, where roof pitches range from nearly flat on mid-century ranches to steep on newer builds in developments north of Loop 1604, the wrong flashing angle is the most common compatibility mistake we see from previous repairs. If the original flashing wasn’t installed with the right kickout at the eaves, water slides past it and runs down the fascia instead of into the gutter.
OEM versus aftermarket for GAF flashing is worth understanding. GAF’s accessory line, including their StormGuard leak barrier and Pro-Start starter strips, pairs with standard galvanized and aluminum flashing profiles. We use 26-gauge or thicker metal for step and counter flashing. Aftermarket flashing that’s properly bent and matched to GAF’s underlayment specs performs as well as factory-branded metal. What matters more is the install: the overlap, the sealant choice, and whether the shingle courses tie in cleanly.
Styles & brands we work with
Signs Your GAF Flashing Replacement Is Failing
- Water stains on the ceiling or upper wall, always in the same spot after rain. This means water is entering at a penetration point and traveling along a rafter or ceiling joist before pooling where you see the stain. The leak isn’t necessarily directly above the stain.
- Rust streaks down the roof slope from around a chimney or vent pipe. Galvanized flashing eventually gives up its zinc coating, especially in San Antonio’s long hot summers followed by sudden heavy rain. Once rust sets in, pinholes follow.
- Lifted or curled flashing edges you can see from the ground. Thermal expansion and contraction in Texas heat works metal loose over time. If the flashing has separated from the chimney mortar or pulled away from the wall, water has a direct path in.
- Granules in the gutter below a flashing point, or shingle edges that look chewed up around a pipe boot. This indicates the flashing has been moving against the shingles, wearing them down and breaking the seal.
- Dampness or mold smell in the attic after a storm, even when the roof deck looks dry. Flashing leaks often run down the inside of a vent pipe or behind the chimney chase, never touching the roof deck until they reach the ceiling. By the time you smell it, it’s been leaking for a while.
Replacement Cost & What’s Included
For GAF flashing replacement in San Antonio, here’s what you can expect to pay based on the type of penetration:
| Flashing Type | Typical Installed Range | What It Includes |
|---|---|---|
| Pipe boot / vent collar | $350 – $550 | New boot, sealant, shingle tie-in, debris cleanup |
| Step flashing (wall-to-roof joint) | $500 – $800 | New step flashing per linear foot, counter flashing, reseal |
| Chimney flashing (full replacement) | $650 – $1,200 | Step, counter, and apron flashing, mortar tuck where needed |
| Skylight flashing | $500 – $900 | New flashing kit matched to skylight brand, reseal, tie-in |
The range comes down to two things: access and how much surrounding shingle work the install requires. A steep second-story chimney takes longer than a ground-level pipe boot. If shingles around the penetration are damaged or brittle, replacing them adds to the job.
Every quote from Crestview Roofing Co San Antonio includes the parts, labor, sealant, debris cleanup, and the written price before we start. The number we give you is the number on the invoice. No change orders over “unexpected damage” unless you approve it in writing first. And the 365-Day Done Right Promise covers the entire repair for a full year, in writing, included with every flashing replacement we install.
See the difference
Before
After
Before
After
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AfterDIY or Call Us?
You can safely check a few things from the ground or with a ladder if you’re comfortable on one. Look for visible rust, lifted metal, or shingles that have pulled away around penetrations. Clear debris from chimney crickets and valley flashing. That’s inspection, and it helps you describe the problem accurately when you call.
Replacing flashing is where DIY goes wrong fast. The work requires lifting shingle courses without breaking them, bending metal to the correct angle for your roof pitch, and sealing in a way that handles San Antonio’s heat-and-rain cycles. Get the counter flashing overlap wrong and the leak comes back in six months, usually worse. If the flashing is around a chimney or on a second story, the fall risk is real. That’s a job for a trained roofer with the right ladder setup and insurance. Call us at (361) 209-8857 and we’ll get someone out to look.
FAQs
GAF flashing, properly installed, lasts 15 to 25 years in San Antonio’s climate. The real variable is the sealant, which breaks down much faster under Texas UV exposure and thermal cycling. We often replace flashing that’s structurally fine but leaking because the old sealant has cracked and pulled away.
Call (361) 209-8857 if your flashing is over 15 years old and you’re seeing water stains. We’ll tell you if it needs a reseal or a full replacement.
In some cases, yes. Small lifted edges can be re-sealed, and a single rust spot on an otherwise sound section can be patched with a metal patch and roofing sealant. If the flashing has multiple rust holes, has separated from the mortar, or was installed at the wrong angle, patching just buys you a few months. We’ll only recommend what’s actually needed, and the written price is the same whether it’s a repair or replacement.
Call (361) 209-8857 for an honest assessment.
Most single-point flashing replacements in San Antonio take 2 to 4 hours from setup to cleanup. Chimney flashing with counter flashing and mortar work can take a full day. We’ll give you a time window before we arrive and a live trackable arrival time so you’re not sitting around waiting.
We keep standard pipe boots, aluminum coil stock, step flashing, and counter flashing on the truck, along with sealants matched to GAF underlayment systems. If your chimney or skylight needs a custom profile, we can fabricate it on-site for most standard sizes. For rarer custom skylight kits, we may need a day to order the right part.
Call (361) 209-8857 and describe the component and we’ll tell you if it’s a same-day fix or needs a quick parts order.
Why Crestview Roofing Co San Antonio for GAF Flashing Work
I’m Dylan Pace, and I’ve spent the better part of two decades working roof types across the spectrum, from steep-slope shingle to low-slope modified bitumen and standing-seam metal. My crew has handled GAF systems across San Antonio, including reroof work through the Alamo Heights corridor where chimney flashing and wall-to-roof transitions get tested hard every time a storm rolls through. We approach flashing the same way we approach every job: the price is written before work starts, the work is documented with before-and-after photos, and the guarantee is in writing. Every promise we make goes in writing, because a handshake doesn’t keep water out.
Crestview Roofing Co San Antonio is an independent roofing contractor. We’re not affiliated with GAF, but we install and repair GAF systems and stock GAF-compatible flashing alongside materials from Owens Corning and CertainTeed. The Relay Visibility Guarantee applies to every flashing replacement we do. Live arrival time. Digital invoice by text. A written price that holds. And the 365-Day Done Right Promise: if it’s not done right, we make it right, free of charge, for a full year.
If your GAF flashing has reached the end of its life, call (361) 209-8857 to schedule a free estimate. A live person answers, 24/7.
Written by Dylan Pace, Owner, Crestview Roofing Co San Antonio at Crestview Roofing Co San Antonio, serving San Antonio and nearby areas.