Shingle Roofing in San Francisco

The workhorse of the steep SF slope

Composition, or asphalt, shingle is the most common roofing material on San Francisco’s steep front slopes for good reason: it’s cost-effective, it comes in architectural (dimensional) styles that suit the city’s Victorians, Edwardians, and mid-century homes, and a quality shingle installed correctly holds up well. It’s the material most re-roofs default to for the visible pitched portion of the roof — the part the street sees. What it isn’t is a flat-roof material; the low-slope or flat rear roof that nearly every SF home also has needs a membrane, not shingles, so most whole-home re-roofs here are really two materials on one building.

With shingles, the difference between a roof that lasts its full rated life and one that fails early is almost entirely the install: proper underlayment, correctly woven or metal-lined valleys, tight flashing at every transition and penetration, and the right nailing. Our damp, foggy climate adds one more factor — the north-facing slopes that stay shaded and wet grow moss and lichen, and a shingle roof here benefits from good ventilation and, on chronically shaded slopes, zinc or copper strips at the ridge to keep growth down. A cheap shingle nailed on fast will look fine for a year and then start telling on itself; a quality shingle installed properly is a decades-long roof.

What shingle roofing covers

• Full re-roofs of the steep slope in architectural or 3-tab composition shingle, over new underlayment.
• Repairs — replacing lifted, cracked, or blown-off shingles and the flashing around them.
• Proper flashing and valleys — the details at chimneys, walls, penetrations, and the transition to the flat rear roof that actually keep water out.
• Ventilation and moss control — ridge/eave ventilation and, on shaded north slopes, zinc or copper strips to slow moss.
• Honest tear-off advice — whether the old roof can be worked with or should come off, and whether a second layer over an existing roof is a false economy.

Common questions

How long should a shingle roof last in San Francisco?

A quality architectural shingle, properly installed and ventilated, should give you a long service life — often decades. What shortens it here is the damp: poor ventilation traps moisture, and shaded north slopes grow moss that lifts and degrades shingles if it’s left to build. The roof’s real lifespan comes down to the shingle grade, the quality of the install, and whether the moss and drainage are kept in check. Those are the things that get discussed rather than just quoting a number off the package.

Can I put a new layer of shingles over the old roof?

Sometimes it’s allowed, but it’s usually a false economy. An overlay saves the cost of tear-off up front, but it hides whatever is wrong with the underlayment and deck, adds weight, and typically gives you a shorter-lived roof — and you’ll pay for a full tear-off of two layers next time. On most SF homes the honest recommendation is to tear off and start clean so the underlayment and flashing are right. If an overlay genuinely makes sense for your roof, you’ll hear that too, with the trade-offs laid out.

Do I need to shingle the flat part of my roof too?

No — and you shouldn’t. Shingles are made for slopes; on a flat or low-slope roof they’ll leak because water doesn’t run off fast enough to stay above the shingle laps. The flat rear roof needs a membrane system (torch-down, TPO, or built-up) instead. That’s why a full re-roof on a typical SF home is two materials: shingle on the steep front, membrane on the flat back. A proper quote covers both parts as the different systems they are.

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