Mice in the Walls: Signs, Causes and What to Do

Signs it is mice in the walls

Typical signs:

• Light scratching or scurrying, mostly at night when the house is quiet
• Noise that moves along the wall, up or down
• Droppings in cabinets, drawers or behind appliances on the same wall
• A musky smell near outlets or switch plates
• Pets staring at or pawing a particular wall

Rats are louder, heavier and often gnaw. If droppings are half an inch or larger, it is rats. See rodent noises at night.

How mice get into wall cavities

Wall voids connect to almost everything:

• Plumbing chases under sinks, where pipes pass through the floor or wall
• The gap behind stoves, dishwashers and fridges
• Attic top plates, where interior walls meet the attic
• The crawl space or the gap where the wall meets the slab
• Garage walls shared with the house
• Exterior gaps around pipes, cables and vents

Many early 1900s Memphis homes, especially in Midtown and Central Gardens, have balloon framing, where stud bays run from the foundation to the attic. A mouse in the crawl space can reach the second floor without leaving the wall.

What to do first

Before calling, gather clues:

• Note which wall, how high, and what time the noise happens
• Check under sinks for droppings and gnawed pipe insulation
• Look behind the stove or dishwasher with a flashlight
• Check the garage wall shared with the house

Do not stuff foam into interior gaps or drill holes yet. Blocking an inside opening can trap mice in the wall, where they may die.

How a technician handles it

A technician traces the noise to the likely route, then sets traps at the openings into the wall and along runways nearby, often inside cabinets or in the attic and crawl space. University of California guidance recommends traps close to walls, where mice travel, and no more than about 10 feet apart where mice are active.

Once catches slow, the exterior entry points are sealed with steel or copper mesh, metal and sealant, and interior pipe gaps are closed. Follow-up visits continue until the noise and fresh droppings stop. See mice in walls removal.

Why not poison?

Poisoned mice often die inside the wall. A dead mouse in a wall cavity smells for days to weeks, and finding it can mean opening the drywall. Traps let you remove the mouse. University of California guidance also notes that rodenticides are toxic to pets and people and should be kept out of their reach. See dead rodent smell.

Damage to watch for

Mice gnaw constantly. Inside walls, that can mean chewed wire insulation, pipe insulation and the paper backing on drywall. If you notice flickering lights, a burning smell or warm outlets, call an electrician. Nesting material and droppings inside the wall are another reason not to wait.

Memphis houses and wall voids

House age changes where mice get into walls. In early 1900s homes in Midtown, Central Gardens and Cooper-Young, open stud bays and old plumbing chases connect the crawl space to the attic. Mice often enter at a foundation vent or pipe gap and travel the full height of the house.

In 1950s and 1960s brick ranches in Whitehaven, Frayser and Raleigh, mice usually enter at weep holes, gaps under the brick ledge, or around old gas and plumbing lines, then follow exterior walls toward the kitchen.

In newer homes in Cordova, Bartlett and DeSoto County, the garage is usually the starting point, and the wall between the garage and the house is the first wall to make noise.

Should you open the wall?

Usually not. Opening drywall to chase live mice rarely helps, since they just move to another bay. The better approach is to trap where they enter and leave the wall and to seal the outside.

The exceptions are a dead mouse that cannot be reached any other way, a nest blocking a pipe chase, or wiring damage that an electrician needs to inspect. In those cases, a small, targeted opening is better than a big one. Ask the technician to pinpoint the spot first.

Keeping them out

Mice fit through gaps slightly larger than a quarter inch. Seal pipe gaps under sinks, garage door corners, dryer vents and crawl space vents. Keep food in sealed containers and pet food put away at night. In Memphis, check those seals each fall, when mice push indoors. See mouse control.