Rainy Season Home Prep: A San Diego Roof & Drainage Checklist

San Diego County gets most of its annual rain in just a handful of winter storms, so roof and drainage problems sit hidden for months and only reveal themselves when the first real downpour hits. The fix is to prep before the rain, not during it. Walk this checklist in October or November – clear drainage, check roof flashing and underlayment, and seal window and door penetrations – so small flaws don’t become interior leaks.

Why San Diego homes hide water problems so well

In a wetter climate, a marginal roof or a clogged area drain announces itself early. Here, a home can go eight or nine months without enough rain to test anything. A cracked sealant joint, a lifted shingle, a downspout that dumps against the foundation – none of it matters on a sunny day in July. Then an atmospheric river parks over the county for 36 hours and every weak point leaks at once.

That long dry stretch also does real damage. Intense UV and heat bake roofing materials, dry out caulk and roof cement, and make asphalt shingles brittle. Coastal homes from La Jolla to Oceanside add salt air to the mix, which corrodes flashing, fasteners, and gutter hardware. So by the time the rain arrives, your roof and drainage have spent most of the year quietly degrading with no symptoms to warn you.

The takeaway: dry weather is not proof your home is watertight. It just means the test hasn’t run yet. The point of a pre-season walk-through is to run that test deliberately, on your terms, while repairs are still cheap and the trades aren’t slammed with storm calls.

Drainage: where the water goes after it lands

Most rain-related damage in San Diego is not a dramatic roof failure – it’s water that lands fine and then has nowhere good to go. Start at ground level, because grading and drainage problems cause more foundation and crawlspace trouble than the roof itself.

• Gutters and downspouts. Clear out leaves, jacaranda debris, palm fronds, and the grit that washes off aging shingles. Run a hose into the gutter and watch that water actually reaches a downspout and exits well away from the house. Sagging sections that hold standing water are a sign of failed hangers or undersized gutters.
• Downspout discharge. Water should be carried at least four to six feet from the foundation. A downspout that empties right at the slab is one of the most common causes of crawlspace moisture and slab-edge intrusion we see.
• Grading and slope. The soil around the house should fall away from the foundation, not toward it. San Diego’s expansive clay soils – especially inland in Escondido, El Cajon, and Santee – swell when wet and shrink when dry, and ponding water against the foundation makes that movement worse.
• Area drains and yard drains. Many local homes rely on subsurface area drains to handle patio, courtyard, and slope runoff. These clog with dirt and roots over a dry summer. Flush them now; a blocked area drain backs up and floods exactly where you don’t want it.
• Sump pumps. Less common here than in wet climates, but homes on slopes or with basements may have one. Test it by pouring water into the pit and confirming it cycles on and pumps out.
• Hardscape and slope drainage. Hillside lots in Poway, La Mesa, and the coastal canyons need swales and slope drains kept clear so runoff doesn’t undercut retaining walls or saturate the soil above the house.

The roof: flashing and underlayment do the real work

Homeowners fixate on shingles and tiles, but the parts that actually keep water out are the flashing and the underlayment beneath the surface. That’s also where San Diego’s sun does its quiet damage.

• Flashing at every penetration. Chimneys, plumbing vents, skylights, and the wall-to-roof junctions are the usual leak points. Look for rust, lifted edges, gaps, and dried-out or cracked sealant. Years of UV turn roof cement and caulk hard and brittle long before the roofing itself fails.
• Valleys. Roof valleys carry the most water during a storm. Debris dams and corroded valley metal send water sideways under the roofing instead of down and off.
• Underlayment and tile condition. On the clay and concrete tile roofs common across the county, the tiles are largely a UV shield – the felt or synthetic underlayment underneath is the actual waterproof layer, and it has a much shorter lifespan than the tile. Cracked, slipped, or missing tiles expose that underlayment to sun and accelerate its failure. On older homes, underlayment that has reached end of life will leak even with tiles that look fine from the street.
• Asphalt shingles. Look for curling, cupping, granule loss, and bald spots. Brittle, heat-baked shingles crack under foot traffic and wind, and the granules washing into your gutters are the shingle surface wearing away.
• Low-slope and flat sections. Many San Diego homes have flat or low-slope roof areas where water sits rather than runs off. Check for ponding stains, blistering, open seams, and failed parapet flashing.
• Skylights. Common on local homes and a frequent leak source. Inspect the curb flashing and the gasket or seal around the glass.

Safety first: don’t walk a wet, tile, or steep roof yourself. A lot can be assessed from a ladder at the eaves and with binoculars from the ground. When in doubt, bring in a professional – this is exactly what a roof inspection covers, and the right time to schedule it is before the rain, not after a leak shows up on your ceiling.

Window, door, and wall penetrations

Roofs get the attention, but wind-driven rain finds its way in through walls too. During a storm the rain rarely falls straight down; it’s pushed sideways against the windward face of the house.

• Window and door flashing. Check the exterior caulk joints around frames for cracks and gaps. Failed perimeter sealant lets water into the wall cavity, where it can rot framing and feed mold long before you ever see a stain.
• Wall penetrations. Hose bibs, electrical and cable entries, dryer and exhaust vents, and light fixtures all puncture the exterior envelope. Each needs intact sealant.
• Stucco cracks. Hairline stucco cracks are normal, but wider cracks and gaps at trim and transitions can wick water. Note any that have opened up over the dry season.
• Decks and balconies. Elevated decks and balconies have their own waterproofing that fails with age and sun. (For multifamily and HOA buildings, California’s SB-721 and SB-326 laws now require periodic structural inspection of these – a separate topic, but worth knowing if you own one.)

What you can’t see from a ladder

The most expensive rainy-season damage is the kind that’s already happening inside the wall or attic before any drip reaches the ceiling. Water tracks along framing and insulation and can wet a large area while leaving the visible drywall dry for weeks. That’s where thermal imaging earns its keep – an infrared scan reveals temperature differences from active moisture and missing insulation that a visual inspection alone will miss, so you can catch a slow intrusion before it turns into rot or mold.

When to inspect, and how to stay ahead

Do your own walk-through in early fall, before the first significant storm. That timing gives you room to clear drains, reseal joints, and book any repairs while the trades still have availability. Waiting until water is already coming in means competing with every other homeowner in the county for the same roofer.

If your roof is older, you’ve seen granules in the gutters, or you simply haven’t had eyes on it in a few years, a professional pre-season roof inspection is the smart move – and keeping it on a regular cadence is even better. Our bi-annual roof care approach catches the small flashing and sealant issues twice a year so they never become a winter emergency. A dry San Diego summer is exactly when these problems are easiest to fix and cheapest to ignore – until the rain proves otherwise.