Putting a roof on an addition, an ADU, a new deck, or a building that’s being reframed? Send a few details and one vetted, licensed San Francisco roofer will give you a straight read on the system, the tie-ins, and a real cost range. No callback roulette, no five companies blowing up your phone.
Helpful to know: what’s being built, roughly how much roof area, whether it’s steep or low-slope, and whether it ties into an existing roof or a neighbor’s wall.
You’ll hear back with a real read on the job. Not a script.
Roof installation means putting a roof where there wasn’t one, which is a different job from tearing off an old one and putting a new one back. New construction, a rear addition, an ADU in the back, a deck that needs a waterproof membrane under it, a garage conversion, a dormer. The framing is new, the deck is clean, and the roofer isn’t inheriting anyone’s mistakes.
In San Francisco there’s a catch, and it’s the same catch on almost every job: the new roof has to marry into an old building.
The tie-in is where new roofs leak
The field of a new roof rarely fails. New material, correct fasteners, nobody’s walked on it for twenty years. What fails is the seam where it meets what was already there.
Think about what a typical SF addition is actually doing. A new low-slope membrane over a rear bump-out has to lap into the existing torch-down behind the parapet, step-flash up a hundred-year-old shared wall you can’t touch because your neighbor owns half of it, and die neatly into the steep front slope. Every one of those transitions is an opportunity, and every one of them is where a roof that’s two years old ends up dripping into a bedroom.
Old buildings are also not square, not plumb, and not level, and a Victorian’s rear wall has settled in some direction over 110 years. Flashing an old wall means fitting to what’s there rather than to what the detail drawing assumes. This is the part where craft actually matters and where the cheap bid gets expensive.
Picking the system for what you’re building
Slope decides most of it. If the pitch is 2:12 or less, you need a membrane: torch-down modified bitumen, TPO, or a built-up system. Composition shingles on a low slope will leak, no matter how well they’re installed, because they shed water rather than seal against it. That’s not an opinion, it’s what the manufacturers say in their own installation instructions, and installing below the minimum slope voids the warranty.
Above that, on a real slope, composition or architectural shingles are the workhorse and metal is the upgrade. Near the ocean, in the Sunset or out toward Lands End, specify Galvalume or aluminum rather than plain galvanized, because salt air will find any bare steel eventually.
Decks are a special case people get wrong. A walking deck over living space is a roof first and a deck second. It needs a proper waterproof membrane with the drainage designed in, and the decking floats above it on sleepers or pedestals so water can get to a drain. Building a deck on sleepers over a membrane that was never meant to be a roof is a leak with a five-year fuse.
Title 24, DBI, and the neighbors
New roof area on a low-slope roof triggers California’s Title 24 cool-roof requirements, which means the membrane has to hit a minimum solar reflectance. Practically this is why so many new SF flat roofs are white or light gray. Your roofer should be specifying a compliant product without being asked.
Permitting goes through DBI, and if the building sits in a historic district or is a designated resource, changes visible from the street get an extra layer of review. Worth knowing before you fall in love with standing-seam metal on a Victorian front slope.
Then there’s access, which in this city is a cost driver and not a footnote. No driveway. No parking. Material carried up through the building or hoisted off the sidewalk under a permit, tear-off debris carried back down the same way, and a crew working off a roof they reach through someone’s kitchen. Budget for it. Anyone bidding SF work like it’s a suburb hasn’t done SF work.
What roof installation costs in San Francisco
As of 2026, per roofing square (100 square feet), installed. Access, height, and tie-in complexity move these more than the material does.
- Composition or architectural shingles: $600 to $1,100 per square.
- Torch-down modified bitumen or TPO on low slope: $800 to $1,600 per square.
- Standing-seam metal: $1,400 to $2,500+ per square.
- Waterproof deck membrane with pedestal or sleeper decking: priced by area and drainage design.
- Access, hoisting, permits, and DBI review: itemized separately; they are real.
Common San Francisco roof installation questions
What’s the difference between installation and replacement?
Replacement means tearing an old roof off and putting a new one back on the same structure. Installation means roofing something that has never had a roof: an addition, an ADU, a new deck, a dormer. Different scope, different sequencing with the framer, and usually a different permit.
Can I put shingles on my flat roof?
No. Below roughly 2:12, shingles will leak, because they’re designed to shed water down a slope rather than to seal against standing water. Low slope needs a membrane. If a bidder proposes shingles on a low-slope rear roof, that tells you what you need to know about the bid.
My addition ties into the neighbor’s wall. Is that a problem?
It’s normal here and it does need care. Flashing against a shared or adjoining wall you don’t own has both a technical answer, which is proper counterflashing and a reglet where one is permitted, and a neighborly one, which is a conversation before the crew shows up rather than after. Get it detailed properly. This is the joint most likely to be leaking in five years.
Related San Francisco roofing services
- Roof replacement when the existing roof is at the end of its life.
- Flat roof repair for the low-slope membrane over the rear of the building.
- Skylight installation, best planned into a new roof rather than cut in later.
Send your San Francisco roofing details
What’s being built, how much roof area, the slope, and what it ties into. Describe it and you’ll get a straight answer on system and cost, with no pressure to book.
If a deck is going over any of it, mention that early. It changes the waterproofing entirely.
No cost, no obligation. A clear read from the roofer who’d actually do the work.