Mice exploit surprisingly small gaps around pipes, doors, garages, foundations, and siding transitions. Finding the entry route means following physical evidence from indoors toward the exterior rather than sealing random cracks.
Start where droppings or gnaw marks appear
Look along wall edges, behind appliances, and inside lower cabinets. Grease marks, nesting material, and gnawed food packaging help reconstruct the paths mice are using.
Inspect utility penetrations
Gaps around sink plumbing, HVAC lines, cables, and conduits are common entry points. Shine light from one side when practical and inspect both the indoor opening and its corresponding exterior location.
Doors and garages need true closure
A worn door sweep or open garage-door corner can leave enough room for entry. Adjust sweeps and seals so they close gaps without blocking ventilation openings the building needs.
Seal with rodent-resistant materials
Foam alone can be chewed through. Where appropriate, combine sealant with metal mesh, flashing, or another gnaw-resistant material suited to the surface. If mice are already inside, coordinate exclusion with removal so animals are not trapped in cavities.
Sources
- U.S. Environmental Protection Agency — Integrated Pest Management — Integrated pest management using sanitation, exclusion, monitoring, and targeted treatment.