Seal Entry Points for Mice

Mice can squeeze through openings the size of a dime, which means your house has dozens of potential entry points you've never noticed. They don't need an open door or a broken window — a gap where the dryer vent meets the siding, a crack where the garage door doesn't quite meet the concrete, or the space around a pipe penetration in the foundation are all highways into your walls. Once inside, mice breed quickly and leave behind urine trails that invite more mice to follow. Sealing entry points is the only permanent solution. Traps and poison deal with mice already inside, but sealing keeps new ones from ever getting in. The work requires patience and a systematic approach — you'll crawl around your foundation, inspect every penetration, and fill gaps with materials mice can't chew through. Most homes have 15 to 25 entry points, and sealing them all takes a methodical afternoon, but the payoff is a house that stays rodent-free without ongoing intervention.

1. Find Every Entry Point. Walk the entire exterior foundation with a flashlight, looking for any gap or crack wider than a dime. Check where the foundation meets the siding, around basement window wells, and along the bottom edge of garage doors. Mark each opening with colored tape so you don't lose track of locations when you start sealing.
2. Scout the Hidden Gaps. Examine every spot where utilities enter the house — gas lines, water supply, electrical conduit, cable and phone lines, outdoor faucets, and dryer vents. Mice commonly enter through the gaps around these penetrations because builders rarely seal them completely. Pay special attention to older homes where settling has opened gaps that weren't there originally.
3. Check Doors and Vents. Check weatherstripping on all exterior doors, especially garage doors where the rubber seal often shrinks or cracks. Look at crawlspace vents, attic vents, and soffit vents for damaged screens or gaps around the frame. Test windows by closing them and looking for light coming through — if light gets through, so can mice.
4. Plug Foundation Cracks. Mix hydraulic cement according to package directions and fill any cracks in the foundation wider than a quarter inch. Push the cement deep into the crack with a putty knife, overfilling slightly, then smooth it flush with the foundation. This prevents mice from exploiting small foundation failures that will only grow larger over time.
5. Block With Metal Mesh. Push copper mesh or steel wool into each marked gap until it's packed tight but recessed about half an inch from the surface. Mice can't chew through metal mesh. Then seal over the mesh with exterior caulk for small gaps under a half inch, or expanding foam for larger openings. For pipe penetrations, wrap the mesh around the pipe first, then foam around it.
6. Secure Vent Penetrations. Remove the exterior vent cover and check for gaps between the vent pipe and the wall opening. Seal any gaps with foam or caulk, ensuring the pipe still has room to move slightly with temperature changes. Replace any damaged vent covers with metal models that have tight-fitting dampers, not plastic ones that mice can chew.
7. Upgrade Door Seals. Install new rubber weatherstripping on doors where the current seal is cracked or compressed flat. For exterior doors, add or replace door sweeps so they make firm contact with the threshold when the door closes. Garage doors need new bottom seals if you can see daylight underneath when closed.
8. Reinforce Vent Screens. Check all vent screens for holes or rust damage and replace any that show wear. Use quarter-inch hardware cloth, not window screen — window screen is too weak. Secure hardware cloth with exterior screws every few inches so mice can't pry up edges. Make sure vents remain functional and aren't blocked by the screening.