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

The Sierra and the mountains: 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

Mountain homes and cabins come with a basement or a crawlspace, decks close to the ground and shingle roofs. Many sit closed up for long stretches, which is when mice move in for shelter.

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 foundation line

    Basement or crawlspace, look where the sill meets the foundation, starting at the corners. Cover crawlspace vents with 1/4-inch hardware cloth. Never block a vent.

    The foundation line
  • Low decks and porches

    Look where the deck framing meets the house, and underneath, where it sits close to the ground.

    Low decks and porches
  • Doors

    Check every outside door for daylight at the bottom and sides, including the crawlspace access door.

    Doors
  • Lines into the house

    Pipes, cables and propane or AC lines often come through the wall low down. Check each one with the finger-width rule.

    Utility lines
  • Rooflines and roof returns

    Look up at the soffits and roof returns with a flashlight. Screen soffit vents with hardware cloth and keep them open.

    Roof returns

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).

Most Californians who have had hantavirus were exposed in the state’s interior mountain ranges or the eastern Sierra Nevada (CDPH). In Yosemite, the deer mouse is the main carrier (Yosemite National Park). Opening up a cabin, shed or camper that has been closed for a while is when to be careful: air it out first and clean up the safe way (CDPH).

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. CDPH Vector-Borne Disease Section, 2023 Annual Report
  3. National Park Service, Yosemite, Hantavirus
  4. California Department of Public Health (CDPH), Rabies
  5. Centers for Disease Control and Prevention (CDC), Preventing Rabies from Bats
  6. Centers for Disease Control and Prevention (CDC), How to Clean Up After Rodents
  7. 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.