No Mice Here Mouse-proof my house
Regional guide · California

The Bay Area: the mouse-proof standard.

The same 10 spots, in the order that fits how homes here are built. Every home can be made mouse-proof, and mice come in for shelter, so sealing the gaps is what keeps them out.

How homes here are built

Northern California homes are built in the same styles we seal back east: many have basements and shingle roofs. That puts the sill line, the basement walls and the roofline first on the list.

The mouse-proof standard. Every home can be made mouse-proof. Seal for the smallest invader, the mouse, and you’ve closed the gaps the bigger ones use too. What the standard means →

Where to look first

  • The sill line

    Look where the wood sill sits on the foundation, especially at the corners, and where the siding stops above it.

    The foundation line
  • Lines through the basement wall

    Pipes, cables and AC lines often come in through the basement wall. Check each one with the finger-width rule.

    Utility lines
  • Basement and cellar doors

    Check where an outside cellar door frame meets the foundation, and the edges of the doors when they are shut.

    Bulkhead doors
  • Roof returns

    On shingle roofs, the short return where the roof edge meets the wall is a common gap. Look up from the ground with a flashlight.

    Roof returns
  • Siding corners

    Look behind vinyl corner posts and anywhere two materials meet, like siding and trim.

    Where materials meet

Rats, pigeons and bats use gaps like these too. Seal to the mouse-proof standard and those gaps are closed to them as well: one standard, not a separate fix for each animal.

Check for bats before you seal

Before you seal any gap up high, shine a strong flashlight up into the shadow: rooflines, roof returns, attic and soffit vents. Look for droppings, dark rub stains, a clean hole through the cobwebs, or bats tucked in the gap. If you see any, don’t seal it yourself, because bats need a proper exclusion so none get trapped inside.

Never seal anything in. If something could be living behind the gap, don’t seal it yet. On a two-story house, when in doubt, assume bats. Don’t touch a bat, alive or dead (CDPH). If you think you’ve had contact with one, talk to your health department (CDC).

More on bats in California →

The common mistake: stuffing a gap with steel wool or foam. Mice chew through foam, and steel wool rusts and pulls apart, so the gap opens again. Neither one is a lasting seal.

Mice and hantavirus here

The hantavirus that makes people sick in California, Sin Nombre virus, is spread by deer mice, which are found throughout California (CDPH). CDPH says the best way to prevent it is to keep wild rodents, especially mice, out of your home, workplace, cabin, shed, car or camper (CDPH).

Sin Nombre virus has been found in wild mice in San Mateo County (San Mateo County MVCD). Deer mice live mostly in rural areas or next to open space, and it’s rare for them to infest homes, but they may move into sheds, vehicles and outbuildings that stay closed up for a long time (San Mateo County MVCD). House mice don’t carry the virus (San Mateo County MVCD).

Fever or trouble breathing after being around rodents? Talk to a healthcare provider and mention deer mice (CDPH).

Catch the ones inside once

Once the outside is sealed, catch any mice still inside with enclosed snap traps set along the walls, out of reach of kids and pets. CDPH recommends snap traps, not glue traps or live traps (CDPH). Never poison.

Clean up droppings safely

  1. Open doors and windows for 30 minutes first, and stay out while it airs.
  2. Put on rubber or plastic gloves.
  3. Don’t sweep or vacuum droppings. It puts dust into the air.
  4. Spray droppings and urine with a disinfectant, or 1 part bleach to 9 parts water, until very wet. Let it soak 5 minutes.
  5. Wipe up with paper towels and throw them out in a covered trash can.
  6. Mop or wipe the area with disinfectant, then wash your gloved hands, take the gloves off, and wash your hands again.

Source: CDC, How to Clean Up After Rodents. Asthma or allergies at home? Mouse allergen settles in household dust, and NIEHS researchers linked higher levels at home to more asthma symptoms in people with allergies (Salo et al., 2009). Sealing the gaps and cleaning up this way both help.

CDPH gives California homes the same clean-up steps (CDPH). Your local mosquito and vector control district can help too: find yours on the MVCAC list of member agencies.

Pro matching is in Southwest Florida for now. The free basic check and the guides work anywhere. Not sure what you’re looking at? Send a photo.

Sources

  1. California Department of Public Health (CDPH), Hantavirus Infection
  2. San Mateo County Mosquito and Vector Control District, Hantavirus
  3. California Department of Public Health (CDPH), Rabies
  4. Centers for Disease Control and Prevention (CDC), Preventing Rabies from Bats
  5. Centers for Disease Control and Prevention (CDC), How to Clean Up After Rodents
  6. Mosquito and Vector Control Association of California, Member agencies

Health facts on this page were checked against each source on October 30, 2026.

Find the gaps. Seal them for good. Catch the ones inside once. No poison, ever.