When the rainy season starts, and why this winter deserves attention
The South Bay rainy season runs from about November through March, and roughly four-fifths of a typical year's rain in San Jose falls in those five months, according to a National Weather Service climate summary for the city. A house that stayed dry all summer gets tested hard in a short window. The first storm is when a small problem becomes a visible one.
This year has an added reason to pay attention. NOAA's Climate Prediction Center has an El Niño Advisory in effect and expects a strong to very strong event to hold through the winter. Its seasonal outlook sees an elevated likelihood of above-normal precipitation across much of California, while noting that West Coast confidence is lower than in the Southeast because the range of possible outcomes is wider. Forecasts can miss, so we would not plan around either a flood or a dry year. We would spend one weekend checking the places water gets in.
This guide covers the roof, gutters, drainage around the foundation, windows and exterior wood, projects already under way, and electrical. You need a flashlight, binoculars, a garden hose, and a ladder only for low, safe spots.
Start at the roof
Most roof leaks start at a detail, not in the middle of the shingles. The weak points are the places where something pokes through or two surfaces meet: chimneys, plumbing vents, skylights, and valleys.
From the ground, with binoculars, look for cracked, curled, or missing shingles or slipped tiles. Check the metal flashing around chimneys and vents for lifting, rust, or gaps. Look for debris piled in valleys. Please do not climb onto a roof to check any of this. A fall is a much bigger risk than a leak.
Then go into the attic on a dry day with a flashlight. Look at the underside of the roof boards for dark stains, check the insulation for damp or compressed patches, and note any musty smell or daylight coming through. Also confirm the insulation has not been pushed into the soffit vents at the eaves. Blocked vents trap moisture, and the resulting stains and mold can look like a leak even when the roof is fine.
After the first real storm, check the same spots again. Stains show up when the wood is wet, and a small repair in November costs far less than drywall and insulation in February.
Gutters, downspouts, and where the water goes
A gutter only works if water can get in at the top and out at the bottom. Once the leaves are down, clear the gutters and the downspout outlets, then flush each downspout with a garden hose. If water backs up or trickles out slowly, something is blocked. Also look for gutters that sag or pull away from the fascia, joints that drip, and water that sits in the trough, which means the slope is off.
Overflow matters because it runs down behind the gutter and soaks the fascia board and the wall below it. Our guide to spotting dry rot lists clogged gutters and downspouts among the typical causes.
Then follow the water to the ground. Extensions should carry it at least 4 to 5 feet from the foundation, based on guidance from University of Minnesota Extension and the EPA. A downspout that empties right at the wall can be worse than none, because it dumps the whole roof's runoff in one spot. A splash block or a flexible extension is an inexpensive fix. Avoid pointing the outlet at a crawl space vent or at a walkway that slopes back toward the house.
Grading and the crawl space
Water that pools against a foundation will eventually find a way in, so the ground around the house should slope away from it. The California Residential Code (section R401.3) calls for the ground to fall at least 6 inches in the first 10 feet from the foundation. Patios, walkways, and other hard surfaces within 10 feet should slope at least 2 percent away from the house. Where a lot line or wall makes that impossible, the code allows drains or swales instead.
You can check this by eye. During the first heavy rain, stand outside with an umbrella and watch where the water goes. Look for puddles within 10 feet of the walls, soil that has settled into a dip against the foundation, planting beds or mulch built up against the siding, and a patio that tilts toward the house. Irrigation that sprays the wall all summer is another common cause.
If you have a raised foundation, open the crawl space access on a dry day and look inside again after the first storm. Standing water, wet soil, damp insulation, white mineral crust on concrete, or a musty smell all mean water is getting in. Make sure plants or soil are not blocking the foundation vents. A torn or missing plastic ground cover over the dirt is also worth fixing.
A little pooling can often be fixed with added soil and a corrected slope. Standing water in the crawl space, or a grade that has to be rebuilt, calls for a pro. The right fix, whether regrading, a French drain, or a sump pump, depends on where the water is coming from.
Windows, doors, and exterior wood
Wood that stays wet for weeks starts to rot, and it usually starts at a joint where water can get behind the trim. Walk the house with a screwdriver and check window sills and the trim under them, door thresholds, the bottom edge of the siding, the fascia under the roof edge, and any place a deck attaches to the wall.
Signs to look for include paint that blisters or peels in one spot, caulk that has shrunk or pulled away from the trim, gaps around window frames, and moss or algae on shaded boards. Press the screwdriver tip into any suspect wood. Sound wood resists. Rotted wood feels soft and the tip sinks in. Our dry rot inspection guide walks through the probe test and what a proper repair involves.
Fresh exterior caulk in cracked joints is a cheap and worthwhile fix before the rain. It is not a repair for soft wood or missing flashing. Caulk over rot hides the problem while the damage keeps spreading.
Inside, check the corners of window frames, the edges of ceilings, and the area around skylights after the first storm. Stains, bubbling paint, or a musty smell near a wall mean water is getting in somewhere. Also look for daylight around door edges, which tells you the weatherstripping is worn.
If you have a project under way
Open walls, bare framing, and exposed soil all need a rain plan before the forecast turns. If a crew is working on your house now, ask these questions this week:
- Protection: How is the roof or open framing covered when the crew leaves for the day, and who checks the tarps after a storm?
- Openings: What is covering any window or door openings that are not installed yet?
- Water paths: Where will runoff from the work area go, and are the gutters and downspouts connected on any new roof section?
- Soil: If the project disturbs soil, as an addition, an ADU, or landscape work does, what erosion and sediment controls are in place?
- Schedule: Which tasks are sensitive to weather, and what is the fallback if a storm lands on that day?
Erosion control on soil-disturbing projects is required. The City of San José says all construction and demolition projects must comply with its Grading Ordinance, and it uses October 15 through April 15 as the rainy season for grading permits. Other jurisdictions use other dates. Santa Clara County's guidance, for example, says rainy-season grading usually runs October 1 through April 30. Ask your contractor which dates apply at your address.
Interior work such as cabinets, tile, and paint is largely unaffected by weather. Roofing, siding, stucco, and foundation work depend on the forecast. A winter start can work well when the crew plans for rain, and most of that planning happens before the first day on site.
Electrical and outages
Storms bring outages, and wet weather exposes weak spots in outdoor wiring. Check outdoor outlets, exterior lights, and the area around the meter and panel for cracked covers, missing weatherproof gaskets, rust, or signs of moisture. An outlet that trips every time it rains is telling you water is getting in. Stop resetting it and have an electrician look.
If you own a portable generator, decide where it will run before you need it. The CDC says to use generators only outdoors, more than 20 feet from windows, doors, and vents, and never inside a home or garage, even with the doors open. The Consumer Product Safety Commission warns that carbon monoxide can build up within minutes in an enclosed space, and it recommends battery-operated or battery backup CO alarms in the home.
Whole-house backup power, such as a standby generator with an automatic transfer switch, is electrician's work. Plan it with a licensed electrical contractor before the first outage rather than during one.
A one-weekend checklist
Everything above fits into one weekend, and none of it requires climbing onto the roof.
Saturday morning, from the ground
- Roof: Scan with binoculars for missing or lifted shingles and damaged flashing.
- Gutters: Clear them and flush every downspout.
- Downspouts: Add extensions or splash blocks so water lands at least 4 to 5 feet from the foundation.
- Grade: Look for soil sloping toward the house, mulch against siding, and sprinklers hitting walls.
Saturday afternoon, wood and openings
- Wood: Probe sills, thresholds, fascia, and deck connections with a screwdriver.
- Caulk: Re-seal cracked joints and replace worn door weatherstripping.
Sunday, inside and underneath
- Attic: Look for stains, damp insulation, and blocked soffit vents.
- Crawl space: Check for standing water, wet soil, and blocked vents.
- Electrical: Inspect outdoor outlets and lights, and decide where a generator would run.
- Insurance: Ask your agent about flood coverage, which generally takes 30 days to start.
After the first storm
- Repeat the walk: Look for stains, pooling water, and anything that drips or trips a breaker.
Frequently asked questions
When should I do this prep?
Before the first sustained storm, which for most South Bay homes means late October through mid-November. If you are reading this later, do it anyway. Plan a second look after the first storm, and a wood inspection in late February, when our dry rot guide says wood is at its wettest.
What does the El Niño forecast mean for my house?
A wetter winter is more likely than usual, but it is not certain. NOAA's Climate Prediction Center expects a strong to very strong El Niño through the winter and sees an elevated likelihood of above-normal precipitation for much of California. It also notes a greater range of possible outcomes on the West Coast than in the Southeast. Preparing costs a weekend and a few supplies, and it pays off whether the winter turns out wet or ordinary.
Does homeowners insurance cover storm and flood damage?
It depends on the policy and the cause, so ask your agent. California's Department of Insurance says most homeowners policies exclude flooding, mudslides, and debris flows, though some may cover certain water damage from wind-driven rain. It also says flood insurance generally takes effect 30 days after purchase. We are contractors, not insurance advisers, so confirm the details with your agent.
Which jobs can I do myself, and which need a pro?
Gutter cleaning, downspout extensions, fresh caulk, and small grade corrections are reasonable DIY jobs if you stay on the ground or a low ladder. Leave roof repairs, flashing, structural rot, standing water in the crawl space, and electrical work to licensed professionals.
When to call a contractor
Call a licensed professional if you find damaged roof flashing or slipped shingles, soft or crumbling wood, standing water in the crawl space, water that keeps pooling at the foundation, or fresh stains on a ceiling or wall.
Monte Builders handles repairs for dry rot and water damage, including sub-frame replacement, siding repair, and framing, as well as window and door weather-sealing and threshold rebuilds. The water source gets identified before anything is rebuilt. Estimates are free, and we reply to every inquiry within one business day. To start, request an estimate.
We work with homeowners in San Jose, Santa Clara, Mountain View, Los Gatos, Milpitas, and Morgan Hill.
