Get your San Francisco home ready for a super El Niño rainy season

The first storm of a wet winter does more damage than the fifth. Leaves that have sat in a gutter since August go down the spout all at once, and a roof that has been dry since April finds out where its flashing has cracked. This winter the Bay Area has a forecast worth taking seriously, so here is the work in the order it pays off, written for the houses that actually stand here: flat roofs behind parapets, garages at the sidewalk, and windows that have been painted shut since the 1950s.

#El Niño 2026 in one minute

On September 10, NOAA's Climate Prediction Center put the odds of a very strong El Niño this fall and winter at more than 90%, and gave a 75% chance that October through December brings a historic event, stronger than any recorded since 1950 (NOAA Climate Prediction Center). Eleven days later Governor Newsom proclaimed a statewide state of emergency and directed state agencies to stage sandbags and pumps ahead of the storms (Office of the Governor). NOAA's next update is due October 8.

What that means for one house on one block is less certain than the headlines. El Niño tilts the odds toward a wet California winter; it does not promise one. San Francisco's own record shows both sides: the very strong El Niños of 1982-83 and 1997-98 brought 38 and 47 inches of rain downtown, while the very strong one of 2015-16 brought about 23, close to an ordinary year. The city's emergency department makes the point that matters for a house: how quickly rain falls counts, not just the season's total, and a single storm can do serious damage in a winter that ends up normal (SF Department of Emergency Management). On December 31, 2022, downtown San Francisco took 5.46 inches in one day, its second-wettest day since records began in 1849 (National Weather Service).

Season totals are from Golden Gate Weather Services' record of downtown rainfall; the average is NOAA's 1991-2020 normal for the downtown station.

When does the rainy season start in San Francisco?

The SFPUC describes the rain season as typically October through April, but the bulk of it falls later: by NOAA's 1991-2020 normals, November through March brings about 84% of downtown San Francisco's yearly rain, and December is the wettest month at 4.76 inches (NOAA). This year the National Weather Service outlook the city cites favors a wetter than normal December through February in Northern California. Treat the end of October as your deadline: gutters, drains and the easy sealing done before the first soaking storm, not after it.

#The work, in the order it pays off

Here is the whole job on one page. The first list needs no ladder. The second is what to finish before the first big storm. The third is where most people should hand off, because it means a roof, a second-story ladder, a sewer line or a permit. Tick items off as you go; your progress stays on this device.

#Roofs, flashing and the flat-roof drain nobody checks

Most San Francisco leaks do not start in the middle of a roof. They start where something interrupts it: a chimney, a vent stack, a skylight, the joint where a parapet wall meets a flat roof. The stucco row houses of the Sunset and the Richmond typically have a flat roof behind an ornamented parapet (SF Planning). On those roofs water collects at a low point, runs to an area drain, and from there usually into a downspout inside the building (SFPUC).

That is why one wad of leaves can flood a whole ceiling. The residential code requires a second, emergency overflow drain or scupper wherever a parapet would trap water if the main drain backs up (2024 IRC R903.4.1), and it is fair to ask whether your roof has one. Look from the ground, not from the roof: a wet roof is slick, and the fall is the injury roofers fear most.

San Francisco requires a permit before roofing material is installed, repaired or removed (SF.gov), and whoever does the work should hold a C-39 Roofing license, which takes a minute to check at the CSLB.

#Gutters and downspouts, the cheapest insurance you can buy

An overflowing gutter does its damage quietly. Water runs behind it, soaks the fascia board, wicks into the top of the wall, and shows up months later as blistered paint or a soft window sill. The SFPUC's advice is to clear downspouts and clean gutters before and after the rain season (SFPUC). With trees close to the house, plan a second pass in midwinter, once the last leaves are down.

Where the downspout empties matters as much as the gutter. The EPA's Indoor airPLUS specification asks for roof water to discharge at least 5 feet from the foundation on sloping ground (EPA). On a San Francisco lot that usually means an extension or a splash block, not a trench across the yard. If your downspout disappears into the ground, run a hose into it on a dry day. If the water backs up, the buried pipe is clogged and the next storm will go into your foundation instead of away from it.

The ladder is where gutter cleaning goes wrong. OSHA's rule is one foot out at the base for every four feet up, with the rails reaching 3 feet above the edge you step onto (OSHA). On a two or three story row house with a narrow side yard, there is often nowhere safe to set that ladder. That is the moment to hand the job off.

#Keep water moving away from the walls

The ground around a house should fall away from it, and the code puts a number on it: at least 6 inches of fall within the first 10 feet, with drains or swales where a lot line or a neighbor's wall makes that impossible (2024 IRC R401.3; the 2025 California Residential Code says the same).

Plenty of older Bay Area lots never had that slope, or lost it to years of mulch piled against the wall. Rake the beds so they fall outward, keep soil off the siding, and watch where water stands during the next rain. A puddle against the foundation is the clearest instruction your house will ever give you.

Water that reaches the foundation shows up below the floor first: a musty crawlspace, dark soil, rust on nails and hangers. Standing water under the house after a storm is a job for someone who does waterproofing and drainage. On a hillside lot the water may be arriving from uphill, which is a drainage design question that can involve retaining walls, not a shovel.

#Windows, doors and stucco: where sideways rain gets in

San Francisco rain rarely falls straight down. It arrives on a southwest wind and finds the joints in a wall: the caulk around a window frame, the gap under a door, the crack where stucco meets trim. The rule of thumb is to weatherstrip the parts that move and caulk the gaps that don't.

In the next storm, check the inside corners of your windows and the sills for wet spots and fresh staining. Cracked, shrunken caulk is a quick fix. Rot under the paint is not. Press a screwdriver into the bottom rail and the sill, and if it sinks in, the window needs repair before it needs caulk. The old weight-and-pulley sash windows that let in rain usually let in drafts too; the drafts guide covers those.

Stucco is the Sunset's other weak point. A hairline crack is usually cosmetic. A wide or stepped crack, or one running from the corner of a window, can let water behind the finish, where it stays. That repair belongs to someone who does stucco and siding. The small jobs, fresh caulking and sealing and new weather stripping, are classic handyman work.

#Garages at the sidewalk, and the sewer under them

The tuck-under garage is San Francisco's classic flood point. The driveway slopes toward the garage door, the street gutter fills, and water runs in under the door. The SFPUC's own list of places that have historically flooded in heavy storms includes 17th and Folsom in the Mission, where a new stormwater tunnel is not due to finish until 2030 (SFPUC). If your garage has flooded before, three things help: a clear drain in front of the door, a tight seal along the bottom of the door, and sandbags placed before the storm rather than during it.

Under the garage sits a second problem. San Francisco has a combined system: stormwater and sewage share the same pipes (SFPUC). In a hard storm those pipes fill, and water can push back up a house's sewer line and out of its lowest drain, often a garage floor drain or a toilet below street level. A backwater valve is a flap on that line that closes when water flows toward the house. The SFPUC explains which properties need one and says to have it checked before every rainy season (SFPUC).

You own your sewer lateral, the pipe from the house to the city main, and keeping it clear is your job. If an SFPUC inspection finds that the lower lateral needs repair or replacement, the agency says that under most circumstances it will do that work at no extra cost after a 311 report.

#City help you can use this winter

• Free sandbags

  San Francisco residents and businesses can pick up as many as 10 at the Public Works operations yard, Marin Street and Kansas Street gate, Monday to Saturday, 8 a.m. to 2 p.m. Bring proof of address and plan to load them yourself.

  Open the official page

• The flood grant

  The SFPUC Floodwater Grant helps owners whose property flooded from the sewer or the street during heavy rain pay for flood protection. It is taking applications now.

  Open the official page

• AlertSF and 311

  Text your ZIP code to 888-777 for alerts. Call 311 for flooding and sewer backups that are not life-threatening, and 911 for anything that is.

  Open the official page

• Adopt a Drain

  Volunteer to keep one of the city's 25,000 storm drains clear through the winter. One clear grate can keep a whole block dry.

  Open the official page

#Storm week: before, during and after

1. Two days out

   Last checks

   Clear the curb drain again, set sandbags at the garage or a low door, charge phones and power banks, and park off the lowest streets.

2. When it starts

   Watch, don't climb

   Look for water where it should not be: at window corners, under the garage door, in the crawlspace. Stay off roofs and ladders, and never walk or drive through moving water. Six inches of it can knock you down (Ready.gov).

3. If water gets in

   People first

   Call 911 for anything life-threatening, including a downed power line, and then PG&E. If you smell gas, leave and call 911, then PG&E at (800) 743-5000. For flooding or a sewer backup that is not an emergency, call 311.

4. If the power goes out

   Generators stay outside

   Never run a generator in the house or the garage, even with the door open. The CDC says to keep it outdoors and more than 20 feet from the house, its doors and its windows (CDC).

5. Within 48 hours

   Dry it out

   The EPA says to dry wet materials within 24 to 48 hours to prevent mold (EPA). Photograph everything before you throw anything away. The first 48 hours after a leak guide walks through it.

6. After it passes

   Walk the house again

   Check ceilings and the attic, look at the gutters, and write down every place water showed up. That list is your repair list for the next dry week.

#Why October beats December

Every roofer, gutter cleaner and drainage contractor in the Bay Area is about to get the same call at the same time. On September 25 a San Francisco roofer told the SF Standard: “This is going to be an insane season for roofers” (The San Francisco Standard).

Book the roof check while the sky is clear. In January you wait behind everyone who didn't.

The same roofer had a warning worth repeating: do not sign anything from someone who shows up at your door saying El Niño is coming, because normal roofers don't sell contracts door to door. Before you hire anyone, look the license up at the CSLB, and read what California law says about hiring a handyman before work starts.