How Mice Get Into Homes Through Gaps the Size of a Pencil.

Gaps cluster where different materials meet or where something passes through a wall. Those are places a builder had to cut, fit and seal, and over years the seal fails.

A flashlight and a few minutes will tell you a lot. Start inside, where signs are easy to see, and go outside after.

• Look under kitchen and bathroom sinks for open pipe holes.
• Check the garage door seal by closing the door at night with the lights on inside and looking for daylight.
• Look at the outside edge of the slab and the base of walls for cracks.
• Check dryer, bath and attic vents for covers and screens.
• Look at the roof edge from the ground, and from a ladder only if it is safe.

If you can slide a pencil into a gap, treat it as an entry point.

Rodents chew soft materials, so the fix has to be harder than a tooth. Metal flashing, hardware cloth and mesh packed into a gap and sealed in place are common choices. Foam alone does not hold, and caulk alone does not either.

• Mesh or hardware cloth for larger gaps, fastened on and sealed.
• Metal collars around pipes where practical.
• Replacement seals for garage doors.
• Metal screens for vents.

Our rodent exclusion page explains the order of work and the materials.

If you suspect an animal is inside, do not plug the hole. An animal sealed in can die in a wall and cause odor, or chew another way out. A technician removes the animal first, then closes the entry.

If you have already closed a gap and hear scratching, call and say what you did.

Write down where each gap is and take a photo. If you want to fix a few yourself, start with the accessible ones. For the roofline and anything hard to reach, hire a professional.

To see what the plan would involve, see mouse control. If you are not sure whether it is a mouse at all, an inspection names the animal.

Mice follow edges and feel their way with their whiskers. A gap that looks closed from standing height may open at the back, behind trim or inside a wall. They also use the same gap again and again, leaving rub marks and droppings along the route.

That is why the inspection looks for evidence, not only for holes. A line of droppings at the base of a wall points to the route, and the route points to the gap. Following it is faster than testing every seam in the house.

A seal fails slowly. Weather, movement and animals test it over time. A check once a season catches small failures early, and it takes less time than any one repair.