The way to keep mice out of your house is to close the gaps they use to get in and take away the reasons they want to. That sounds simple, and it mostly is, but the gaps are smaller than most people expect.
A house mouse can get through an opening about the size of a dime.
In Southern California, where mice stay active all year, cool winter nights push more of them toward the warmth of a house, so now is when the sealing pays off. Here is where to look and what works.
If you already have mice inside, our rodent control service can handle the trapping and the sealing.
Why mice come inside in winter
Mice do not hibernate. When nights drop into the 40s and 50s here, a garage or a wall void beats a burrow in the yard. Food matters as much as warmth: a house has pet food, a pantry, and crumbs, and outside, the summer seed and insect supply has thinned out. We cover the seasonal pattern in more detail in why rodents move indoors as OC temperatures drop.
One mouse rarely stays one mouse for long. A female can have a new litter every few weeks, so a pair in October can turn into a real infestation by spring.
Where mice get into Southern California homes
Most of the guides you will find were written for houses with basements and wood siding. Homes here are different, and so are the entry points.
The garage door
This is one of the easiest ways in. The rubber seal along the bottom of the garage door cracks and shrinks in the sun, and the corners where the door meets the frame often leave a gap. Close the door, turn off the garage light, and look from inside. If you can see daylight, a mouse can get through.
The weep screed on stucco walls
Most stucco homes here have a metal strip, called a weep screed, along the bottom of the exterior walls where the stucco meets the foundation. It lets moisture drain out. It also often leaves a gap between the stucco and the slab that a mouse can slip into, and from there into the wall. Look closely along the base of the walls, especially behind bushes where you cannot see it from the yard.
Pipes, lines, and vents
Every place something passes through the wall is a candidate: AC lines, the gas line, hose bibs, cable and phone lines, and dryer vents with missing or broken flaps.
Raised foundations and crawlspace vents
Older homes with raised foundations have screened vents into the crawlspace. If a screen is torn or rusted out, the crawlspace is open, and mice can reach the house from there through gaps around plumbing.
Doors
Exterior doors without a sweep, or with a worn one, and the door between the garage and the house.
How to seal the gaps
Use materials mice cannot chew through:
Steel wool or copper mesh packed into small gaps, then sealed over with caulk to hold it in place
Hardware cloth (quarter-inch metal mesh) over vents and larger openings
A new bottom seal and corner seals on the garage door
Door sweeps on exterior doors and the garage-to-house door
Metal mesh or a sealant rated for pest exclusion along gaps at the weep screed. Do not block the drainage function completely; leave the weep holes clear and close the gap behind it
Foam and caulk alone do not work. Mice chew through both.
If you want the full checklist for the outside of the house, including roof-level openings that matter more for rats, we put one together here: how to rat-proof your Orange County home. Most of it applies to mice too.
Take away the reasons to stay
Sealing does most of the work. Removing the food and shelter around the house makes the rest of the yard less appealing.
In the garage. Move pet food, bird seed, and grass seed into hard plastic or metal bins with tight lids. Bags on the floor are a buffet. Clear out cardboard boxes stacked against walls, since they make ideal nesting spots.
In the kitchen. Store dry goods like cereal, rice, and crackers in sealed containers. Do not leave pet bowls full overnight.
Outside. Pick up fallen fruit from citrus and avocado trees. Keep firewood stacked off the ground and away from the house. Trim shrubs back so there is a clear strip along the foundation where mice have nowhere to hide.
What does not work
A few popular fixes are not worth the money.
Peppermint oil and other scents may bother a mouse for a short time, but they wear off quickly and will not keep mice out of a warm house with food in it.
Plug-in ultrasonic repellers are another one. The research on them is weak, and any effect tends to fade as mice get used to the sound.
Poison inside the house brings its own problem. Mice that eat it often die inside walls, which leaves a smell that can take weeks to clear.
Snap traps are the better tool for mice already inside. Set them along walls where you see droppings, with a small amount of peanut butter.
When to call for help
DIY sealing works well if you catch it early and the gaps are easy to reach. It gets harder when you are seeing droppings in more than one room, hearing scratching in the walls or ceiling, or you have sealed the obvious spots and still have activity. That usually means there is an entry point you have not found yet.
Finding that last gap is where a trained eye helps. Our rodent service starts with a full inspection inside and out to find the entry points and nesting areas. We set interior traps, seal the smaller entry points, and offer exclusion work for bigger openings. Your first service includes three complimentary trap checks, and if rodents return during the guarantee period, we come back at no charge. We cover homes across Orange County and the Inland Empire.
If mice have already found their way in, request a free quote or call (949) 943-5000. Hearing them overhead instead of in the walls? That points to rats, and our guide to getting rats out of the attic covers what to do.
Frequently asked questions
What is the best way to keep mice out of my house?
Seal the gaps. A mouse can fit through an opening about the size of a dime, so close gaps under the garage door, around pipes and lines, along the base of stucco walls, and under exterior doors using steel wool, copper mesh, or metal hardware cloth.
Why do I have mice in my house in winter?
Cooler nights push mice toward warm shelter, and a house offers warmth, food, and water in one place. In Southern California they are active all year, but activity indoors usually rises in fall and winter.
What smells keep mice away?
Peppermint oil and similar scents are often recommended, but they wear off quickly and will not keep mice out of a warm house that has food in it. Sealing entry points and storing food in sealed containers work far better.
Do ultrasonic mouse repellers work?
The evidence is weak. Any effect tends to fade as mice get used to the sound. Sealing entry points is a better use of the money.
How do mice get into a house with no obvious holes?
Through gaps most people do not notice: the bottom of the garage door, the gap behind the weep screed at the base of stucco walls, openings around AC lines and pipes, dryer vents, and torn crawlspace vent screens.
Can one mouse turn into an infestation?
Yes. Mice breed quickly, and a female can have several litters a year. If you have seen one, set traps and check for entry points right away.
