How to keep mice out of your house this fall: seal, clean up and know when to call a pro
Published October 31, 2026
Where mice get in, how to seal gaps with steel wool and caulk, what to clean up outside, and when to bring in pest control for exclusion work.
When nights turn cold, mice look for warm places to nest, and a house with a few small gaps is an easy target. Trapping and baiting deal with the mice already inside, but the lasting fix is exclusion: closing the openings so new ones can’t get in. Most of it can be done in an afternoon with inexpensive materials.
How small a gap is too small?
The CDC says a mouse can fit through a hole the width of a pencil, about ¼ inch (6 millimeters). The National Park Service’s rodent exclusion manual uses the same ¼-inch rule: find and close every hole, crack or gap that size or larger. That makes the job bigger than it sounds, because gaps tend to be where utilities enter the house.
Where to look inside
The CDC suggests checking:
- Inside, under and behind kitchen cabinets, and behind appliances.
- Around pipes under sinks and washing machines, and pipes that run to water heaters and furnaces.
- Around floor air vents and dryer vents.
- Around the fireplace and in closet corners.
- Around all electrical, water, gas and sewer lines.
- In the attic, the basement and the crawl space, and around floor drains.
- Between the floor and the wall.
Where to look outside
- Roof edges: rafters, gables, eaves and soffits.
- Around windows and doors, especially ones without weatherstripping.
- Between the foundation and the ground.
- Around attic and crawl space vents.
- Around holes for electrical, plumbing, cable and gas lines.
- Clothes dryer vents: the exhaust flap should close easily and not be propped open by lint (National Park Service).
How to seal the gaps
- Fill small holes with steel wool, then put caulk around it to hold it in place. Spray foam also works, according to the CDC.
- Cover larger holes with hardware cloth, lath screen, cement or metal sheeting. The National Park Service manual recommends ¼-inch hardware cloth for mice.
- Cut material to fit snugly around pipes, and don’t forget the garage and outbuildings.
- Keep door thresholds under ¼ inch, and use weatherstripping or a door sweep (National Park Service).
- Check again after storms and in spring. Weather and settling can open new gaps.
Make the yard less inviting
The EPA suggests removing the things that give rodents food, water and shelter:
- Remove nesting sites such as leaf piles and deep mulch next to the house.
- Keep kitchen garbage in containers with tight-fitting lids.
- Turn compost piles so newly added food scraps are covered.
- Stop feeding outdoor birds while you are controlling an infestation, or use only huskless items that leave less residue.
- Clean up spilled pet food and keep human and pet food in sealed containers.
Signs you already have mice
The EPA lists droppings around food packages, in drawers or cupboards and under the sink; shredded paper, fabric or plant matter used as nesting material; chewed food packaging; holes chewed through walls and floors; and stale smells from hidden areas. Follow the CDC’s guidance on safe cleanup before you sweep or vacuum droppings or nests.
When to call a pro
Consider a pest control company when you see signs of mice after sealing, when the entry points are on the roof or in places you can’t safely reach, or when there are too many to handle with traps. The CDC says a pest control specialist can help when rodents have gotten into areas that can’t be reached to clean. Ask for exclusion work and not just trapping or bait, and ask for the entry points they found and sealed in writing. Because exclusion prices depend on the size, age and construction of the house, compare written quotes for the same scope.
Put it on the calendar
Early fall is the best time to seal gaps, before mice move indoors. A free Estodia account adds an annual “seal gaps and check for pests” task to each home’s plan and lets you request pest control quotes without sharing your phone number or email with pros.
Sources: CDC: How to seal up to prevent rodents; CDC: Controlling wild rodent infestations; U.S. EPA: Identify and prevent rodent infestations; National Park Service: Rodent exclusion manual (PDF).
Quick answers
How do mice get into a house?
Through gaps as small as about ¼ inch (the width of a pencil), especially where pipes, wires, vents and gas lines enter the house, around doors and windows, and between the foundation and the ground.
What is the best material to seal mouse holes?
The CDC suggests filling small holes with steel wool and putting caulk around it, or using spray foam. For larger holes use hardware cloth, lath screen, cement or metal sheeting.
When should I seal gaps to keep mice out?
Early fall, before mice move indoors for the winter. Recheck after storms and in spring.
Does cleaning up the yard help?
Yes. The EPA suggests removing leaf piles and deep mulch near the house, using tightly lidded garbage cans, covering compost, and not leaving pet or bird food out.
Do I need a pest control company for mice?
Not always. Sealing gaps is a good do-it-yourself project. Call a pro if you keep seeing signs after sealing, if entry points are hard to reach, or if there are many mice. Ask for exclusion work, not just bait.