Most of us imagine a mouse slipping in through a crack in a wall. In practice, the route is often a plain, unremarkable opening that has been there for years: a pipe collar that never fit, a vent screen that rusted, a garage door seal that curled. You can find these on a single walk.
Before you start.
Choose a dry day when the light is good, though you can walk at dusk with a flashlight to spot daylight at the base of walls. Bring a pencil. If it fits into a gap, a mouse may be able to follow. Note each opening on a rough sketch of the house.
Stop 1: ground level.
- The foundation top, where mortar meets siding or sill plate.
- Cracks in the foundation wall, especially at corners.
- Basement window wells and the frames of small windows.
- Gaps beneath steps, porches and the edge of a slab.
The lowest stop yields the most findings, since animals meet it first. Probe mortar joints gently with a screwdriver. Crumbly mortar is a flag.
Stop 2: utilities.
Look for every place a pipe, wire or cable passes through the wall. This includes gas, water, electric service, air conditioner lines, cable and satellite wiring. The opening around the line is rarely tight.
| Opening. | Common problem. | What holds. |
|---|---|---|
| Pipe through a wall. | A loose ring of space around it. | Steel mesh packed in, then sealant. |
| Cable or conduit. | Unfilled hole larger than the cable. | Mesh plus cured sealant. |
| Dryer vent. | Flap stuck open or missing cover. | A metal hood with a screen. |
| Crawl space vent. | Loose or rusted screen. | Hardware cloth in a metal frame. |
| Garage door. | Curled bottom seal, gaps at corners. | A new seal and a rebuilt threshold. |
Stop 3: doors and windows.
Check the bottom of every exterior door. A door sweep that does not touch the threshold, or a weatherstrip that has worn away, leaves a slot. Hold a flashlight inside at night and look from outside for light. Garage doors are the most common weak spot, because the rubber ages and the corners lift.
Stop 4: the roofline.
Binoculars help from the ground. Look at the soffits, where the roof overhang meets the wall, and at the fascia boards, the gable vents and the ridge. Gaps where two roof sections meet are common. Branches touching the roof are bridges.
Rooflines are high and often unsafe for amateurs. If you see signs of chewing or gaps, photograph them and ask a technician to inspect. See sealing with steel and mesh for how we close them.
Does your attic or cellar match this picture? Give dispatch the details and ask what such signs usually point to.
(551) 274-5838What materials hold and what to skip.
- Holds: stainless or galvanized steel mesh, hardware cloth, sheet metal flashing, masonry patch compound, cured sealant.
- Fails: foam alone, caulk alone, plastic, rags, paper, wood filler.
Steel wool is sometimes recommended, but animals can pull it out, and it rusts. If you use it, treat it as a backing behind metal and sealant.
Different houses, different weak points.
Houses here went up over many decades, so their weak spots differ. Old footings may show crumbling mortar or fieldstone with wide joints. Additions and dormers leave seams where new framing joins old. Newer homes can have gaps beside pipes and cables that nobody filled. Each house earns its own list.
After the walk.
Rank your findings by size and height. Close the low, large ones first, with a short list for a weekend. Larger projects can be added to a plan after a walk-through and quote. If animals are already inside, book trapping first.
Walk the house each year in autumn, and repeat after any construction, storm or roof work.
Small precautions before the visit
You may tidy up before the technician comes, as long as you follow the order below and pause whenever a step confuses you.
- Dry rags raise the same cloud a broom does, so keep them for other chores.
- CDC guidance asks you to ventilate a closed area before cleaning, and a half hour is the figure it gives.
- Keep your hands covered for the entire job and wash them with soap and water when the gloves come off.
- Wetting everything down keeps dust grounded and gives the disinfectant time to act.
- Used towels, droppings and any dead rodent all go into one plastic bag, which you knot and put out with the weekly trash.
- When you see a doctor about any illness, mention the cleanup, since the clinician needs that detail.
Pages behind this advice
Direct links to the agency pages follow.
- EPA limits for rodenticide sales and use: Background on why bait products now ship in enclosures.
- CDC walkthrough for rodent cleanup tasks: Advice on dealing with urine stains, pellets and chewed nest material without kicking up dust.