7 Places Mice Get Into Midwestern Homes Before Winter

Fall home maintenance • Northern Illinois

The first chilly nights are a good reminder to check your furnace, put away the garden hose, and take a closer look at your home’s exterior. For homeowners in Naperville, Woodridge, and across Northern Illinois, fall is also a useful time to look for openings that could let mice inside.

Mice don’t need a wide-open door. According to the CDC’s rodent prevention guidance, an opening about 1/4 inch across can be enough. A house that looks well sealed from the driveway may have several gaps worth investigating up close.

Use these seven places as a starting point for your pre-winter inspection.

1. Garage Door Corners and Bottom Seals

Start where the garage door meets the floor, especially at the two bottom corners. Check for torn weather seals, uneven contact, and visible daylight with the door closed. Inspect the side door and the door connecting an attached garage to the house, too.

What to do: Have worn seals replaced and doors adjusted for a close fit. Keep the garage closed when it isn’t in use.

2. Gaps Around Utility Lines

Follow cable, electrical, plumbing, and air-conditioning lines to the points where they enter the building. The opening around a line deserves attention even when the line itself looks secure. Include unused openings left by old installations.

What to do: Have gaps closed with durable materials suitable for the penetration. For openings near wiring or gas equipment, involve the appropriate professional.

3. Foundation Openings and Siding Transitions

Walk the perimeter and look at the foundation, damaged mortar, and the transition where siding meets the structure below it. Take photos of questionable openings so you can compare the exterior location with what you see in the basement.

What to do: Repair actual entry openings with materials appropriate to the wall. Don’t indiscriminately fill intentional drainage openings or brick weep holes; have their purpose checked first.

4. Exterior Door Thresholds

Back doors, basement walkouts, and side entrances deserve the same attention as the front door. Check the sweep, threshold, and lower frame with the door fully closed.

What to do: Replace damaged weatherstripping and correct gaps. Put door repairs on the fall maintenance list instead of waiting until snow collects at the threshold.

5. Basement Windows and Window Wells

Look around basement window frames for loose trim, deteriorated seals, and damaged screens. Clear leaves from window wells so the frame and surrounding wall are visible during your inspection.

What to do: Repair the window assembly and surrounding openings. Keep drainage and emergency escape functions clear.

6. Crawl Space Vents and Access Doors

Check vent covers and crawl space access panels for damage or gaps around their edges. A cover can look intact from a distance while fitting poorly against the wall.

What to do: Repair or replace damaged components with suitable rodent-resistant protection. Preserve required airflow, and have a professional evaluate openings connected to mechanical equipment.

7. Soffits, Eaves, and Roofline Gaps

Your inspection shouldn’t stop at ground level. Mice are capable climbers, and damaged soffits, loose fascia, and openings around attic vents can offer another route into the house.

What to do: Inspect from the ground and arrange professional access for higher repairs. Avoid climbing onto a roof to investigate a suspected mouse opening.

Choose Repairs That Hold Up

A quick squirt of expanding foam alone isn’t a dependable mouse barrier. University of California IPM guidance recommends durable exclusion materials and notes that mice can gnaw through foam and other soft materials. The right repair depends on the opening and the building surface.

Also check for signs that mice are already indoors. The EPA lists droppings, chewed food packaging, and shredded nesting material among the clues. Store food securely, reduce clutter, and address active mice along with entry-point repairs. Sealing the exterior alone won’t remove mice already inside.