Getting Ready for El Niño in the Bay Area: Gutters, Downspouts, Drains, and Rain Barrels
As of its September update, NOAA's Climate Prediction Center gives a greater than 90% chance of a very strong El Niño this fall and winter. On September 21, the Governor declared a statewide state of emergency to get California ready for it. His advice to the rest of us was short. Clear drains and gutters, sign up for alerts, and make a plan.
Here's the part that gets lost. El Niño tilts the odds toward a wet winter. It doesn't guarantee one, especially up here. The National Weather Service office in Sacramento counts six very strong El Niños since 1950, and Northern California got two wet winters, two normal ones, and two dry ones out of them. In 1997-98, San Francisco got about double its normal rain. In 2015-16, the last very strong one, Hayward got 84% of normal.
The good news is that getting ready costs the same either way, and most of it is an afternoon with a ladder. Here's where mesh helps, and where it doesn't.
Gutters: Clean Them, Then Guard Them
Cal OES puts it plainly. When gutters back up, they can overflow and cause damage and flooding to your home. Over 80% of San Francisco's rain falls between November and March, so October is the window. The rain doesn't always wait, though. On October 24, 2021, an atmospheric river dropped 4.02 inches on downtown San Francisco in a single day, which the Weather Service called unusually early for the region.
Clean them first. A guard over a gutter that's already full of leaves just hides the problem.
Then think about a guard, because this time of year your gutters have two jobs. Right now, in Diablo wind season, dry leaves in a gutter are a place for embers to land. In a month, the same leaves are what make it overflow. If you're building new or remodeling in a mapped fire hazard area, California's Wildland-Urban Interface Code (Section 504.4) requires gutters and downspouts to be noncombustible, with an approved way to keep leaves and debris out of the gutter. Existing homes don't have to retrofit, but a metal guard covers both seasons either way. For the rest of the fire side, see our pieces on ember-resistant vents and California's Zone 0 rule.
UC's wildfire guide for homeowners notes that there's no standard way yet to test how gutter guards perform, so we won't rank brands. Here's how we think about the mesh itself. A finer opening keeps out smaller debris. More open area lets more water through when it's really coming down. Every guard trades one against the other, and none of them means you never get on a ladder again.
Downspouts: Keep the Water Moving Away
A coarse screen where the gutter drains into the downspout keeps leaves from plugging the pipe, which is a much worse job to fix than a gutter. At the bottom, the City of Hayward says to make sure downspouts direct water away from foundations. The Department of Energy's building guidance says at least 5 feet away. A downspout that dumps next to the house just moves the flood to your crawlspace.
Storm Drains: Clear Them, Don't Cover Them
Hayward's stormwater guidance says clearing the storm drain inlets near your home, when it's safe, can help prevent backups. Work from the sidewalk and leave the grate where it is. Oakland's adopt-a-drain program flatly says lifting it is unsafe. If one is clogged and you can't clear it, call Hayward Public Works at (510) 881-7900. We wouldn't put mesh over a street drain. It's one more thing to clog, and it's the city's drain.
Hayward also hands out free sandbags, up to six per household, at a self-service station at 16 Barnes Court that's open around the clock. It's for residents of the city itself, so bring ID. Worth grabbing before the first big storm instead of during it.
Rain Barrels: Screen Them or Raise Mosquitoes
A wet winter is a good reason to catch some of it, and Hayward suggests rain barrels. The catch is that standing water is exactly where mosquitoes lay eggs. The Alameda County Mosquito Abatement District says to use a mosquito-proof screen, fine mesh of 1/16 inch, under the lid and over the overflow hole. For cisterns, it says to cover every inlet, outlet, and vent the same way. The CDC's version is that the holes have to be smaller than an adult mosquito.
Standard 18 x 14 insect screen is the usual choice. If you want a number you can check against the district's 1/16 inch (0.0625), our 16 mesh aluminum in .018 wire has a 0.044 inch opening.
If you're a Hayward water customer, the city offers a $50 rebate per rain barrel through BAWSCA, up to two for a single-family home. The barrel needs rust-proof screening or a sealed design to qualify, which is one more reason to get the screen right.
Crawlspace Vents: Leave Them Open
When the rain starts blowing sideways, it's tempting to block the foundation vents. Don't. Those vents are there to let moisture out of the crawlspace, and the Department of Energy's crawlspace guide warns that simply sealing the vents could make the situation worse, increasing the levels of moisture. Closing a crawlspace properly is a real project with a vapor barrier and conditioning, not a sheet of plastic.
What you can do is make sure the screens are intact, because fall is also when mice start moving indoors. The code caps crawlspace vent openings at 1/4 inch. Our rodent-proofing guide covers which mesh to use.
What We'd Use
| Job | What we'd use | Opening | Open area |
|---|---|---|---|
| Gutter guard | 8 Mesh aluminum, .028" wire | 0.097" | 60% |
| Finer, stiffer gutter guard | 1/16" hole on 1/8" staggered perforated aluminum, .032" | 0.0625" | 23% |
| Downspout screen | 4 Mesh aluminum, .047" wire | 0.203" | 66% |
| Rain barrel and cistern openings | 16 Mesh aluminum, .018" wire or 18 x 14 aluminum insect screen | 0.044" (16 mesh) | 51% (16 mesh) |
| Crawlspace vents | 4 Mesh 304 stainless, .035" wire | 0.215" | 74% |
Aluminum doesn't rust and it's light enough to work with on a ladder, which is why it's most of this list. If you're near the bay or the ocean and want something that lasts longer, ask about stainless in the same sizes.
Frequently Asked Questions
Does El Niño mean a wet winter in the Bay Area?
It raises the odds. It doesn't guarantee it. Southern California's link to El Niño is much stronger than ours, and the last very strong El Niño in 2015-16 left Hayward below normal. NOAA updates its forecast every month, so check back as winter gets closer.
When does the rainy season actually start?
Most Bay Area rain falls from November through March, but early storms happen. The October 2021 atmospheric river is the reminder. Doing this in October means you're done before it matters.
Do I need a gutter guard?
For new construction and remodels in a mapped fire hazard area, the WUI code requires an approved way to keep leaves and debris out of your gutters, and noncombustible gutters and downspouts. For everyone else, it's a trade between cleaning more often and having a guard to check once in a while. Either way, a guard doesn't replace cleaning.
What mesh size keeps mosquitoes out of a rain barrel?
The Alameda County Mosquito Abatement District says 1/16 inch or finer, under the lid and over the overflow. Insect screen does the job.
Should I cover my crawlspace vents for the winter?
No. They're there to let moisture out, and blocking them can make a damp crawlspace worse. Keep the screens intact and the vents open.
We cut aluminum, stainless, and insect screen to size, so you're not buying a full roll for one gutter run or a single rain barrel. Send us the lengths and what it's for, and we'll quote it, or ask for a free sample to see the mesh first. Family-owned since 1938, when we started on Howard Street in San Francisco. Now we're in Hayward, and a real person answers the phone at (510) 887-8787.
This article is general information about wire mesh and home maintenance, not engineering, flood, or building code advice. Forecasts change monthly. For local flood risk and alerts, follow your county's emergency information, and verify code requirements with your local building department.