Mice in the Walls: How to Find Where They Get In

What is that scratching in the walls at night?

Mice are most active from dusk until a few hours before dawn, which is why the sound seems to start when the house goes quiet. Light, quick scratching and pattering inside a wall or ceiling, often near the kitchen or a bathroom, is typical. Heavier thumps and gnawing that you hear in daylight are more likely squirrels, especially in an attic.

Confirm with droppings. Mouse droppings are about the size of a grain of rice, dark and pointed at the ends. You will usually find them in kitchen drawers, under the sink, behind the stove, along basement walls and on top of the sill plate. Fresh droppings look glossy and feel soft; older ones turn dull and crumble.

Once you know what to look for, a slow walk around the house with a flashlight finds most of them in an hour.

Indoor clues that point back to the gap

Mice travel along edges and inside hidden runs, so the trail they leave indoors usually bends toward the opening they use. Check these spots with a flashlight before you head outside, and write down which outside wall each clue sits against. That tells you where to start the walk-around instead of circling the whole house blind.

• Under the kitchen and bathroom sinks, where supply and drain pipes pass through a cabinet floor or back panel through a hole cut wider than the pipe.
• Behind the dishwasher, range and refrigerator, where gas lines, water lines and cords come up from the basement.
• Along the top of the basement foundation wall, where droppings pile up on the sill plate directly inside an outside gap.
• Around baseboard heating pipes and radiator lines that drop through oversized holes in the floor.
• At the bottom of basement and attic doors with no sweep, which mice use to move between levels.
• In the garage, behind stored boxes, birdseed or pet food lined up against the wall shared with the house.

How to find where mice are getting in: an outside walk-around

Go out in daylight with a flashlight, a small mirror and a notepad. Work your way around the house in order so nothing gets skipped:

1. 1

   Start where the utilities enter

   Gas lines, the electric service, cable and phone wires, the air conditioning line set and outdoor faucets all pass through the wall. Any gap around them larger than a pencil is a candidate.

2. 2

   Check the garage

   Look at the bottom corners of the garage door, where the seal often ends early or has been chewed, and at the gap between the door frame and the wall.

3. 3

   Follow the foundation line

   Look for cracks, missing mortar, and gaps between the foundation and the siding or the bottom of the wood sill.

4. 4

   Look at vents and openings

   Dryer vents with broken flaps, unscreened crawl space vents and foundation vents are easy entries.

5. 5

   Finish at the roofline

   Use the mirror or binoculars to check where gutters meet the roof, soffit corners and gaps around the chimney. Mice climb brick, downspouts and vines with ease.

How can you tell which gap the mice are actually using?

Not every crack is an active entry. Look for three signs together: dark, greasy rub marks on the edges where fur brushes past, fresh gnaw marks with light-colored wood or plastic showing, and droppings within a foot or two of the opening. A gap with old cobwebs strung across it and no marks around it is probably not in use right now.

To confirm a suspect, push a loose twist of newspaper into the gap or dust a little flour on the ledge in front of it, then check the next morning. Paper pushed aside or tiny tracks in the flour mean traffic. The same trick works after sealing: an opening you missed shows itself within a night or two.

Common mouse entry points and how to seal them

Use durable materials. Mice chew through plain foam, rubber and wood, so the fix needs to resist gnawing.

Mice in the attic: when the entry is up high

If droppings and noise are concentrated in the attic or upper walls, the entry is probably at the roofline. Mice climb surprisingly well, using rough brick, downspouts, vines and tree branches that touch the house. Common openings include gaps at the corners of the soffit, where a newer roof meets older trim, and around attic vents.

Look for greasy rub marks around the opening and droppings on the insulation nearby. Cutting branches back several feet from the roof removes the bridge, but the gap itself still needs sealing with metal, not foam.

Should you seal first or trap first?

Trap first when mice are active inside, then seal within a few days. Sealing a house with mice still in the walls can trap them inside, where they look for new ways out, often into living space. Set snap traps along walls where droppings are heaviest, with the trigger end facing the wall, and check them daily.

Once trap catches slow to zero for several days, seal every opening you found. Then set a few fresh traps to confirm nothing new is getting in. If catches start again, there is an entry you missed.

When to bring in professional help

Call if you cannot find the entry point, if mice keep showing up after sealing, if the gaps are high on the house, or if droppings show up in food storage. Our mouse control service combines trapping inside with a full exterior inspection, and our rodent exclusion work seals the openings with materials mice cannot chew through. The main rodent control page covers rats and other rodent issues too.