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

California: the mouse-proof standard.

Every home can be made mouse-proof. California homes are built in the same styles we seal: basements and shingle roofs up north, crawlspaces through the middle, and slab foundations with block walls down south. Here’s where to look first in each.

The mouse-proof standard

Seal for the smallest invader. Build every seal to keep out a mouse, and you’ve closed the gaps the bigger ones use too.

A young mouse can get through a gap about the width of a finger. The mouse-proof standard means every gap that size or bigger, on the outside of the house, is closed for good: back it with 1/4-inch hardware cloth (stainless or heavy galvanized) or exterior-grade metal, then seal it in with polyurethane, RTV or acetoxy construction sealant. Vents stay open, with hardware cloth over them. Weep holes are never plugged solid.

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.

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.

Where to start, by how your home is built

North: basements and shingle roofs

Mountains: cabins and closed-up homes

Central: crawlspaces

South: slab foundations and block walls

Next door: Nevada

Every region starts with the same 10 spots. Mice come in for shelter, so Check my house works for any house.

Bats: check first

Check for bats before you seal

California has many kinds of bats, in rural, suburban and city areas, and they may roost in attics (CDFW). In California, bats and skunks are the animals that most often get rabies (CDPH).

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).

Bats are protected in many places. Check your local rules on timing before you exclude them.

Mice and hantavirus in California

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).

Deer mice live mostly in rural areas, the desert and the mountains, and house mice don’t carry the virus (San Diego County)(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. California Department of Public Health (CDPH), Rabies
  3. California Department of Fish and Wildlife, Human-Wildlife Conflicts: Bats
  4. Centers for Disease Control and Prevention (CDC), Preventing Rabies from Bats
  5. County of San Diego, Department of Environmental Health and Quality, Hantavirus
  6. San Mateo County Mosquito and Vector Control District, Hantavirus
  7. Centers for Disease Control and Prevention (CDC), How to Clean Up After Rodents
  8. 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.