The first big storm can turn a small leak into a major headache in San Francisco. With microclimates and steep hills, one block can see heavy rain while the next stays dry. You want to protect your home, avoid surprise repairs, and feel ready when the forecasts start flashing flood alerts. This guide gives you a simple, local checklist with what to do before, during, and after storms, plus city resources you can use right now. Let’s dive in.
Know your San Francisco rain risk
San Francisco’s rainy season typically runs from roughly November through April, with annual rainfall around 24 to 25 inches depending on the station and neighborhood microclimate. You can see month-by-month precipitation context for central SF using NOAA station summaries on climate charts, which highlight how variable winters can be. Review historical patterns on the San Francisco station page for useful context about wet and dry years (San Francisco precipitation overview).
Flooding here is often driven by stormwater runoff and the city’s combined sewer system. Use the SFPUC’s 100‑Year Storm Flood Risk Map to check a specific parcel’s stormwater flood risk and learn about preparedness steps. The map focuses on intense stormwater events and does not show all flood types, such as coastal or groundwater rise (SFPUC flood maps and guidance).
Pre-season checklist (September to October)
Roof and drainage basics
- Inspect the roof for missing shingles, cracked flashing, clogged valleys, or sagging lines. Schedule a professional if the roof is older or shows damage. Small fixes now prevent expensive leaks later.
- Look inside the attic for stains, musty smells, or daylight at penetrations. Confirm insulation and ventilation are in good condition.
Gutters and downspouts
- Clean gutters and flush downspouts so water moves off the roof and away from the foundation. Add extensions that discharge several feet from the house or into approved drains.
- Plan to clean at least twice per year, with extra visits if trees drop heavy debris. Professional cleanings in urban Bay Area markets commonly fall in the mid-hundreds per visit, depending on size and access (gutter cleaning cost ranges).
Site grading and surface drains
- Walk the property after a light rain. Fill low spots that pond near the foundation and re-establish shallow swales so water flows away from the structure.
- Clear surface drains and drive-channel grates. Elevate stored items in garages or basements to reduce damage if water enters (SFPUC flood-readiness tips).
Basements, garages, and backflow
- Test sump pumps and backup power. Consider a battery backup or secondary pump if you have a history of water intrusion.
- Talk to a licensed plumber about a backwater valve where sewer surges are a risk. Standard homeowners policies usually exclude sewer or drain backups unless you add an endorsement, so prevention matters (sewer backup coverage basics).
Windows, doors, and sealant
- Re-caulk window and door trim and seal exterior penetrations. Replace worn weatherstripping to reduce drafts and moisture entry.
Trees, slopes, and retaining walls
- Trim dead or overhanging limbs to protect the roof and keep gutters clear.
- Inspect retaining walls, slope drains, and hillside areas for cracks or movement. Intense rain can trigger slope issues; consult a professional if you see warning signs (landslide and heavy-rain context).
During the rainy season
Storm-day routine
- Clear leaves and litter from nearby street drains. You can volunteer to keep a specific catch basin clear through the city’s Adopt a Drain program, which helps reduce localized flooding (how to adopt a storm drain).
- Place sandbags to divert water from doorways and garage entries if your site is prone to pooling. The city provides free sandbags during storms with limits per address and posted pickup details (sandbag pickup updates).
- Check that your sump pump is running and that downspout extensions are attached.
After a big storm
- Walk the interior and exterior. Look for new stains on ceilings, damp baseboards, water in low-level rooms, or erosion outside.
- Dry wet materials quickly and consider a dehumidifier in damp areas to reduce mold risk.
- Photograph any damage for insurance and future repair planning.
Longer-term resilience and local help
Grants and flood tools
- If your property has experienced flooding from the public right-of-way or combined sewer system, explore SFPUC Floodwater Grants that can help pay for on-property projects like barriers, backflow prevention, trench drains, and permeable paving. Check eligibility and application details directly with SFPUC (Floodwater Grants and map info).
Permits and pros
- Simple maintenance like gutter cleaning or minor roof patching usually does not require a permit, but structural repairs, retaining wall work, and major plumbing changes often do. Check current rules with DBI and plan timelines accordingly. Local reporting highlights ongoing permit-tracking efforts and timing considerations (permit process context).
Insurance and disclosures in San Francisco
- Standard homeowners policies generally exclude flood damage from surface water or overland flooding. If you are at risk, ask about flood insurance options through NFIP or private carriers and review waiting periods before coverage starts (flood insurance overview and resources).
- Sewer or drain backups are also usually excluded unless you add a specific endorsement. Review your policy language so you know what is and is not covered (sewer backup coverage basics).
- In San Francisco, sellers and landlords must disclose if a property is within the SFPUC 100‑Year Storm Flood Risk Map zone. Use the parcel lookup to check an address and get prepared (SFPUC flood maps and guidance).
Quick supplies and contacts
- Keep basic supplies ready: sandbags, plastic sheeting, duct tape, work gloves, and a flashlight with fresh batteries.
- Sign up for AlertSF and keep an emergency kit. For storm updates and small business alerts, see recent city guidance and reminders to call 311 to report flooding or clogged drains (city storm alerts and tips).
Preparing early protects your home and gives you peace of mind when the forecast turns stormy. If you are planning to buy or sell soon, getting rain-ready also helps inspections go smoothly and preserves value. For local, strategic guidance that pairs practical know-how with high-touch real estate service, reach out to Cooper Gaines.
FAQs
When should a San Francisco homeowner start rain prep?
- Start in September or October so your home is ready before November rains, then do a mid-season tune-up after the first big storm. City preparedness notices reinforce early action during rainy years.
How can I check if my SF address is in a stormwater flood zone?
- Use the SFPUC 100‑Year Storm Flood Risk Map’s parcel lookup to see stormwater flood risk for your address and understand the map’s scope and limits.
Where can I get sandbags in San Francisco before a storm?
- San Francisco Public Works distributes free sandbags during storm periods with limits per address and posted pickup details on city update pages.
What low-cost steps reduce water intrusion risk at home?
- Clean gutters and nearby street drains, add downspout extensions, re-grade small low spots, elevate valuables in garages, and test your sump pump.
Are floods or sewer backups covered by a standard homeowners policy?
- Flood damage is typically excluded and often requires separate flood insurance; sewer and drain backups are usually excluded unless you add a specific endorsement.
