Free roof inspection with deck photos before we talk money - GAF and Owens Corning certified installation
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AfterGAF Roofing in San Francisco, CA | Mercer Roofing
If you need GAF roofing service in San Francisco, here’s the short version: Mercer Roofing is our Roofing Company in San Francisco that installs and repairs GAF flat-roof membranes and shingles across the city’s Victorian and Edwardian rowhouses, the Sunset’s stucco homes, and everything between. The thing that makes GAF work here different is fog. Not rain, not wind, but Karl the Fog sitting on your flat roof for weeks at a stretch, and the rowhouse next door sharing your party wall. Our crews know exactly what that does to a GAF Liberty cap sheet or an EverGuard TPO seam, and we price the work accordingly. Call (743) 200-8347 for a written estimate before anyone touches your roof.
Why San Francisco Residents Choose Us for GAF Service
Plenty of roofing companies can say they work with GAF products. Far fewer can tell you what a GAF EverGuard TPO seam does when it’s installed over a pre-1940s built-up roof in the Richmond District and then asked to survive five fog seasons. Our founder, Grant Whitlock, learned the structural side of roofing at Los Angeles Trade-Technical College, and he’s spent going on two decades reading roofs before touching them. That habit matters here. In San Francisco, you don’t get the big dramatic failures you see in storm-driven climates. You get slow, quiet saturation that hides behind a parapet cap until the ceiling below starts staining. We look for it before it finds you.
We’re independent. GAF doesn’t authorize, sponsor, or endorse us, and we don’t claim otherwise. What we have is hands-on experience with GAF Timberline HDZ, EverGuard TPO, RubberGard EPDM, and Liberty modified bitumen systems on San Francisco’s flat and low-slope housing stock. Our technicians are background-checked, identity-verified, and photo-badged under the Threshold Verified standard. Before anyone arrives at your door, you get their name and photo. They badge in when they show up. Written price first. Written guarantee on every repair. That’s how we’ve operated since 2000 as part of the Threshold Group family.
Common GAF Roofing Problems We Solve in San Francisco
- Granule loss and surface crazing on GAF Liberty modified bitumen. In the Outer Sunset and Inner Richmond, the marine layer keeps flat roofs damp for weeks. The membrane’s granule surface starts shedding, then hairline cracks form at the seams. It looks like sun damage, but it’s moisture-driven. We cut out the saturated section and re-seal with GAF-compatible flashing and termination bars.
- Algae streaking on GAF Timberline HDZ shingles. The pitched roofs that do exist in San Francisco are mostly on Twin Peaks and a few Sunset homes. North-facing slopes stay wet for months. Algae doesn’t destroy the shingle on day one, but it traps moisture and shortens the service life. We treat it and, when the shingle is compromised, replace the affected courses.
- Party-wall flashing failures on zero-lot-line rowhouses. In the Castro, Mission, and Western Addition, GAF TPO and EPDM membranes terminate at shared walls. Building movement and heat from the attached home next door break those terminations open. Fog moisture tracks in through the gap and into the ceiling assembly. We re-flash the termination properly and rebuild the seal.
- GAF EverGuard TPO seam delamination over old BUR substrates. A lot of pre-1940s Sunset and Richmond homes still have their original built-up roof underneath a newer TPO membrane. The TPO bridges low spots, and foot traffic plus thermal cycling peels the seams apart. Patching the seam without addressing the substrate doesn’t hold. We identify the bridge, address it, then re-weld.
- Ponding water at interior drains on GAF flat roofs. When a GAF membrane sags around an interior drain, water sits instead of flowing. In fog-heavy neighborhoods, that standing water never fully dries. The membrane degrades at the drain collar. We restore the slope, replace the drain flashing, and re-secure the membrane so water actually leaves the roof.
GAF Service in San Francisco: What Local Conditions Mean for Your Equipment
Here’s the thing a general GAF page won’t tell you. San Francisco’s Victorian and Edwardian rowhouses are zero-lot-line, which means there is no side yard. None. When we replace a GAF flat roof in the Castro or along Dolores Street in the Mission, every roll of membrane, every sheet of insulation, every length of termination bar has to be hoisted over the front parapet by rope and pulley, or carried through your living room. This is not a quirk. It is a measurable labor cost that affects nearly every GAF membrane re-roof on San Francisco’s attached housing stock. A bid that doesn’t account for hoisting over a parapet is a bid written by someone who hasn’t done the job here. We stage every GAF job in the flatlands around that reality: smaller material lifts, protected parapet caps, and a plan for your interior if the stairs are the only path. It changes how long the job takes and what it costs, and we put it in writing up front.
In the Outer Sunset, we worked on a 1930s stucco rowhouse where a GAF Liberty modified bitumen roof had been ponding and leaking at the parapet for years. The homeowner said it started as a small stain, then one day the ceiling just gave up. Our crew hoisted new GAF Liberty cap sheet and termination bars over the front parapet with rope and pulley. We cut out the saturated section, re-flashed the party-wall termination, and restored the interior drain. That was two fog seasons ago. The roof has held without re-saturating. That’s the difference between knowing GAF systems and knowing GAF systems in San Francisco.
GAF Models & Products We Service in San Francisco
We install and service the GAF product lines that actually show up on San Francisco roofs: GAF Timberline HDZ asphalt shingles for the city’s handful of pitched roofs, GAF EverGuard TPO single-ply membrane for flat and low-slope commercial and residential work, GAF RubberGard EPDM for older low-slope roofs, and GAF Liberty self-adhered modified bitumen base and cap sheets, which remain the workhorse for re-covering the Sunset and Richmond District’s pre-war flat roofs. We use genuine GAF accessories wherever they’re available: termination bars, seam tapes, flashing components. GAF’s warranty system depends on matched components, and we don’t cut corners there. When lead times or compatibility demand it, we substitute quality aftermarket fasteners and drain hardware. You’ll always know what’s going on your roof and why. For a deeper look at how we approach the brand, visit our GAF sales & service page.
GAF Service Pricing in San Francisco
Nobody can quote our Roof Repair in San Francisco over the phone, but here’s what homeowners should expect. A small GAF Liberty patch with flashing repair typically runs $400 to $900, depending on access. A party-wall termination rebuild on a zero-lot-line rowhouse runs $1,200 to $2,800. A full GAF Liberty or EverGuard TPO re-roof on a typical Sunset or Richmond flat roof falls between $8,000 and $22,000, with the hoist-over-parapet labor adding $800 to $2,500 depending on the roof height and material volume. What drives the price here is access, not just square footage. A suburban re-roof backs a truck to the house. Here, we park at the curb and move everything by rope or through your front door. The estimate is free, it’s written, and it doesn’t change once work starts. Call (743) 200-8347 to schedule yours.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs – GAF Roofing in San Francisco
GAF Timberline HDZ performs well on pitched roofs, but in San Francisco’s fog belt the north-facing slopes will collect algae and moss. The shingle itself handles the moisture fine; the biological growth on the surface is what shortens its life. If you’re installing in Twin Peaks or the Sunset, we recommend a preventive algae-resistant treatment at installation and periodic cleaning. Call (743) 200-8347 and we’ll walk your specific roof before you commit to anything.
Yes, if the damage is isolated. A split seam, a failed termination bar, or a punctured cap sheet can often be repaired with genuine GAF accessories and the repair will hold. If the membrane is saturated through, or it’s past roughly 75% of its service life, patching becomes a losing game. We’ll tell you which one you have, and the inspection is free.
Rain is episodic: it comes, it drains, it dries. Fog is chronic: weeks of continuous moisture, low light, and no drying cycle. On GAF TPO and EPDM, that means micro-cracking and seam degradation at the fog edge, even when your roof has never had standing water. It also accelerates biological growth that retains additional moisture. The damage pattern looks different from storm damage, and it requires a different repair approach. That’s why we inspect for saturation, not just visible leaks.
No. In fact, on San Francisco’s zero-lot-line rowhouses, there is no side access to be had. We hoist membrane rolls, insulation, and flashing over the front parapet with rope and pulley, or we carry materials through the interior when the parapet height makes hoisting impractical. It costs more than a suburban install, but we account for it in the written estimate so there are no surprises on the invoice.
For a low-slope roof in the Outer or Inner Sunset, GAF Liberty self-adhered modified bitumen is the most common choice because it handles persistent moisture better than TPO in continuously damp conditions. GAF EverGuard TPO is an option if the roof has positive slope and the substrate is sound. We’ll recommend the right system after we see the roof’s condition, drain locations, and fog exposure. Estimates are free; call (743) 200-8347 to set one up.
Service Areas Near San Francisco
Mercer Roofing serves all of San Francisco service area, from the Outer Sunset to the Bayview. We also work with homeowners across the Bay Area and beyond. For GAF service in the Central Valley, see our GAF service in Fresno page. For the capital region, visit GAF service in Sacramento.
Book Your GAF Service in San Francisco Today
You’ll get a written price before any work starts, a photo-badged technician whose name you already know, and a 365-Day Done Right Promise in writing. A roof that’s doing its job is one you never think about. Let’s keep it that way. Call (743) 200-8347 to schedule your free estimate.
Written by Grant Whitlock, Owner at Mercer Roofing, serving San Francisco since 2000.