Mouse-proofing your house comes down to two things: sealing every gap larger than a dime and eliminating the food sources that attract mice in the first place. A house mouse can squeeze through any opening it can fit its skull into, which means holes as small as 6 to 7 millimeters are fair game. The good news is that a thorough inspection and a weekend of work can dramatically reduce your risk.
Find Active Entry Points First
Before you start sealing anything, you need to know where mice are actually getting in. Walk the exterior and interior of your home looking for physical evidence: small dark droppings about the size of a grain of rice, dark grease smudges along baseboards or around holes (left by oily fur rubbing against surfaces), fresh gnaw marks on wood or plastic, and shredded paper or insulation tucked into corners.
Sketch a rough floor plan and mark every spot where you find signs. This map tells you where to focus first. If you suspect a particular gap but aren’t sure it’s active, sprinkle a thin line of flour or talcum powder on the floor in front of the opening. Check it after 24 hours. Fresh tracks through the powder confirm that gap is in use and should be your top priority.
Seal the Exterior
The most common entry points on the outside of a house are utility penetrations (where electrical, gas, water, and A/C lines pass through walls), gaps along the soffit line where the roof meets the walls, foundation cracks, and weep holes in brick veneer. Start at ground level and work your way up, checking every pipe, wire, and conduit that enters your home.
Utility Penetrations and Foundation Gaps
Gaps around pipes and wires are best filled with materials mice can’t chew through. Copper mesh or stainless steel wool stuffed tightly into the gap, then sealed over with caulk, creates a durable barrier. Expanding spray foam alone is not enough. Mice chew through standard foam easily. If you use foam, back it with metal mesh first. For larger foundation cracks, a combination of metal mesh and concrete patch holds up better long-term.
Weep Holes
If your house has brick walls, weep holes along the bottom course of brick are essential for draining moisture from the wall cavity. You can’t just plug them shut. Stainless steel weep hole covers with small punched holes (around 1.6mm diameter) block mice, cockroaches, and wasps while still allowing airflow. These screens are typically made from marine-grade 316 stainless steel and press directly into existing weep holes. They’re inexpensive and take seconds to install per hole.
Roofline and Soffit Gaps
Mice are decent climbers and will use overhanging branches, downspouts, or textured siding to reach your roofline. Inspect where the soffit meets the fascia board and where gable vents sit. Any gap along these joints should be sealed with metal flashing or hardware cloth (wire mesh with openings no larger than 6mm). Trim tree branches back at least 3 feet from your roofline to cut off that climbing route entirely.
Don’t Forget Doors and Garages
Standard door sweeps wear down over time and leave just enough gap for a mouse to slide under. Replace worn sweeps with rodent-resistant versions that incorporate stainless steel mesh or bristle barriers. Check the bottom corners of every exterior door, where the weatherstripping often pulls away from the frame.
Garage doors are one of the most overlooked entry points. The rubber seal along the bottom of a garage door degrades, cracks, and shrinks, leaving gaps at the edges and center. Rodent-proof garage door seal kits use stainless steel reinforcement built into the rubber to prevent chewing. These replace your existing bottom seal and also double as weather stripping against wind and rain. Pay special attention to the corners where the garage door meets the track, since that small triangle of daylight is more than enough space for a mouse.
Control Food Sources Inside
Exclusion is half the equation. The other half is making your home uninteresting to mice in the first place. Mice are opportunistic and will eat almost anything, but they’re especially drawn to grains, seeds, pet food, and crumbs.
Store dry goods like cereal, rice, flour, and pasta in hard-sided containers with tight lids. Glass, thick plastic, or metal all work. Thin plastic bags and cardboard boxes are no obstacle for a mouse. Keep pet food in sealed bins rather than leaving bags open in the pantry or garage. Pick up pet bowls at night rather than leaving food out. Clean up crumbs under appliances, behind the stove, and under the toaster regularly. These invisible food deposits are a buffet for mice.
Birdseed stored in the garage and fallen seed beneath outdoor feeders also draw mice close to the house. If you feed birds, keep seed in a metal bin with a lid and clean up spillage underneath feeders frequently.
Eliminate Shelter and Clutter
Mice nest in undisturbed clutter: cardboard boxes stacked in the garage, old newspapers, piles of fabric, or insulation in crawl spaces. Reducing hiding spots makes your home less hospitable even if a mouse does get inside. Store items in plastic bins with lids instead of cardboard. Keep storage areas organized so you can spot droppings or nesting material early. Outside, move firewood piles, lumber, and dense ground cover at least 20 feet from your foundation.
Why Ultrasonic Repellers Don’t Work
Ultrasonic plug-in devices are heavily marketed as an easy mouse solution, but controlled testing has consistently shown they don’t deliver. Studies reviewed by the USDA National Wildlife Research Center found these devices produced only a 30 to 50 percent reduction in mouse movement activity at best, and mice habituated to the sound within 3 to 7 days, after which the devices had no measurable effect at all. A wide range of frequencies and volume levels were tested, and strong, sustained repellent effects were never detected.
The EPA took legal action against several manufacturers for false advertising and misbranding, resulting in fines and court orders. Electromagnetic pest devices fared even worse in testing, showing no effect on feeding, drinking, mating, or infestation patterns. Save your money and spend it on caulk, steel mesh, and proper door seals instead.
Peppermint Oil and Other Natural Repellents
Peppermint oil is a popular home remedy, but there’s no reliable evidence it prevents mice from entering or staying in a home. Any effect from the scent is temporary and fades as the oil evaporates. Mice living in walls, attics, or crawl spaces are unlikely to encounter enough concentration to be deterred. Like ultrasonic devices, natural repellents don’t address the actual problem: open entry points and accessible food.
A Seasonal Maintenance Routine
Mouse-proofing isn’t a one-time project. Mice are most likely to push indoors in fall as temperatures drop, so late summer is the ideal time for your most thorough inspection. Walk the perimeter of your home, re-check every seal and caulk joint, and replace any weatherstripping that has cracked or pulled loose. Inside, inspect behind appliances and in storage areas for fresh droppings or gnaw marks.
A quick check in spring is also worthwhile, since winter weather can crack caulk and shift foundation materials. The homes that stay mouse-free long-term are the ones where small gaps get caught early, before a mouse ever discovers them.