San Francisco has more flat and low-slope roofs than almost any city in California. Sunset District stucco homes, Victorian rooftops hidden behind parapets, Mission flats and SoMa commercial buildings all depend on a membrane that has to shed water with little or no slope. Ace Roofing & Construction has specialized in these roofs since 1996.
We repair, re-coat and replace flat roofs using torch-down modified bitumen and TPO single-ply membranes, and we pay close attention to the parts that cause most failures: drains, scuppers, parapet flashing and low spots that hold water.
What makes SF flat roofs fail
Ponding water is the number one enemy of a flat roof. After a winter storm, a low spot that stays wet for days will break down a membrane far faster than the rest of the roof. Clogged drains — leaves, debris, even pigeon nesting — make it worse, and a blocked drain on a roof surrounded by parapets can fill like a bathtub.
Parapet walls are the second big issue. Where the membrane turns up the wall, the flashing and the cap on top of the wall have to be sealed correctly, or water gets behind the system. In fog-belt neighborhoods the constant moisture also accelerates rot in wood decking under a failing membrane.
Materials & methods
Torch-down modified bitumen
Multi-ply system fused with heat. Very durable and well proven on San Francisco roofs.
TPO single-ply
White, reflective membrane with heat-welded seams, popular on commercial buildings and roof decks.
Crickets and slope correction
Tapered sections that move water toward drains and eliminate ponding.
Drains, scuppers and overflows
New or rebuilt drains plus overflow drains so a single clog does not flood the roof.
Signs you need flat roofing
- Water sits on the roof more than 48 hours after rain
- Blisters, bubbles or cracks in the membrane
- Seams separating or edges lifting
- Leaks near parapet walls or drains
- Soft spots when walking on the roof
- Ceiling stains on the top floor
Our process
- 1
Roof walk and drain check
We inspect the membrane, seams, parapets, drains and any ponding areas.
- 2
Repair vs. replace
We tell you whether patches and drain work will fix it or whether the membrane is done.
- 3
Written scope
Clear description of materials, slope correction and drainage work, with price.
- 4
Installation
Membrane installed and flashed at every wall, curb and penetration.
- 5
Water test and clean-up
We confirm drainage works and leave the roof and site clean.
Repair before replace — our honest approach
A lot of flat roof leaks are drain problems, not membrane problems. One of our customers had a leak other companies wanted to solve with a new roof — we installed a new drain instead.
When a membrane is truly worn out, we will recommend replacement and explain the options between torch-down and TPO for your building.
What a customer said
"Luis is great — hardworking, honest, timely, and smart. He quickly figured out why I had a leak, and rather than overcharging me or selling me something I didn't need (like a new roof), he had his crew install a new drain."
Ryan Gonzalez
January 2024 · Google Review
Flat Roofing FAQs
Torch-down or TPO — which is better for my building?
Both perform well in San Francisco. Torch-down is a proven multi-ply system; TPO is reflective and heat-welded. We recommend based on your roof, use and budget.
Is ponding water on a flat roof normal?
A little water that dries within a day or two is common. Water that sits longer is a problem and usually means a drainage or slope issue.
Can you add a cricket to stop ponding?
Yes. We build tapered crickets and correct slope so water flows to drains.
Do you work on commercial flat roofs?
Yes, including SoMa and Bayview commercial and mixed-use buildings.
Can a flat roof be repaired instead of replaced?
Frequently. Localized damage, failed seams and drain problems can often be repaired. We will tell you honestly what will last.