📋 Steps
1
Inspect with a flashlight at ground level on the exterior
The most revealing inspection technique: get low and look along the foundation with a bright flashlight. Gaps that are invisible standing up are obvious from ground level. Do this inspection in early October before mice seek winter harborage.
2
Seal utility penetrations — the #1 missed entry point
Every pipe, wire, and cable entering the structure through the foundation or sill plate is a potential entry. Fill gaps with copper mesh (stuff into the hole) and seal with paintable caulk or expanding foam. Mice can compress their bodies through any gap a pencil passes through.
3
Install door sweeps on every exterior door
Standard doors have enough gap at the threshold for mice. Install rubber door sweeps (not brush-style — mice chew through brush) on all exterior doors. Check garage doors — the rubber gasket at the bottom is often the largest unprotected gap.
4
Seal gaps where the foundation meets the sill plate
In older construction, the junction between the concrete foundation and the wood sill plate is often cracked or gapped. This continuous horizontal gap runs the entire perimeter and is a major entry highway. Caulk or expand foam this junction thoroughly.
5
Inspect and protect utility boxes and HVAC penetrations
Gas meter boxes, electrical conduit, hose bibs, and HVAC line sets all penetrate the foundation and are common entry points. Check that all conduit and pipe have tight seals at the point of foundation entry.
💡 Tips
- Copper mesh is superior to steel wool for sealing gaps — it doesn't rust and mice don't chew through it as readily as steel wool
- The garage is often the weakest link — gaps under the service door, gaps in the wall where the garage door track attaches, and gaps in siding near the roof line are all common mouse entry points
- Do exclusion work before setting traps — the goal is to stop the flow of new mice while trapping existing individuals
- Inspect the attic for openings above the fascia line — roof rats and mice access attics through gaps at the fascia-soffit junction
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