Every fall, millions of American homes are infiltrated by mice and rats seeking warmth. And every spring, homeowners discover the damage: chewed wiring (a significant house fire risk), contaminated insulation, droppings throughout the walls, and the expensive process of trapping, sealing, and replacing what was destroyed.
Rodent-proofing your home before winter is the single most effective way to avoid all of it. Here's how to do it right.
Know your gaps
A house mouse can compress its body to fit through a gap as small as 1/4 inch — the diameter of a dime. A Norway rat needs just 1/2 inch. This means any gap you can see light through is a potential entry point. The most common entry points are:
- Where utility pipes and wires enter the foundation or walls (look for gaps around gas lines, electrical conduit, and plumbing)
- The gap between the foundation and the bottom of the siding
- Crawl space vents with damaged or missing screens
- The space beneath garage doors (the rubber seal degrades over time)
- Gaps where the roof deck meets the soffit
- Around the dryer vent where the duct exits the house
Materials that actually stop rodents
Not all gap-fillers are equal. Rodents can and do chew through:
- Foam insulation (standard expandable foam is no barrier to a motivated mouse)
- Caulk alone (soft enough to bite through)
- Wood (mice can gnaw through thin wood in hours)
- Plastic screening
What rodents cannot chew through:
- Copper mesh — the ideal fill for gaps before sealing with caulk. Rodents dislike biting metal that shreds their teeth.
- Hardware cloth (1/4 inch galvanized wire mesh) — for larger openings like vents and crawl space access
- Sheet metal — for larger gaps along the foundation or at the garage door threshold
- Concrete/mortar — for cracks in the foundation itself
A room-by-room inspection checklist
Exterior
Walk the entire perimeter in daylight. Bring a flashlight to inspect underneath and behind anything attached to the house. Pay special attention to the area where the foundation meets the sill plate — this junction often develops gaps as the house settles.
Basement and crawl space
Check all utility penetrations. Look for droppings, which indicate existing activity. Inspect the threshold between the crawl space and the house interior.
Attic
Squirrels and rats enter through the roofline. Look for gaps at the soffit, along the ridge vent, and anywhere the roof structure meets the exterior wall. A few hours on a sunny day will reveal light coming through spots that shouldn't have any.
When sealing isn't enough
If you find evidence of rodents — droppings, gnaw marks, nesting material, or sounds in the walls — seal the home after the infestation is eliminated, not before. Sealing active rodents inside just traps them in your walls. A professional can place traps strategically, eliminate the population, and then perform exclusion work in the right order.
