Mice in the Garage: How They Get In and How to Keep Them Out

Mice and rats usually walk into a garage through a door, either one left open or one with a gap under or beside it. To keep them out, close those gaps, keep the doors shut and take away the food and clutter that make the garage worth the trip.

Here is where that comes from. A 1994 chapter on rodent-proof construction in the University of Nebraska-Lincoln wildlife damage handbook, now hosted by ICWDM, says garages are easy for mice and rats to reach through open doors and under or beside garage doors that fit poorly. An overhead door that has warped, sagged or settled onto uneven concrete can leave just that kind of opening.

The opening does not have to be big. The University of Kentucky's entomology extension says a 1/4-inch gap, about as wide as a pencil, lets mice in, and a 1/2-inch gap is enough for a rat. It also points to the bottom corners as a common way in, so start your check there.

The garage is easier to get into, and it often holds more of what rodents want: food in bags, clutter to hide in and long quiet hours with nobody around. It also sits just one wall away from the rest of your home, so treat mice in the garage as an early warning.

Public Health Seattle & King County lists birdseed, pet food, food waste and garbage among the foods that draw rodents, and it warns that if you feed them, they stay. A lot of garages hold most of that list. The same agency names unsecured garages and sheds, along with vehicles, appliances and old furniture, as places where rodents take shelter.

A parked car is on that shelter list too. If you have found nesting material or chewed wires under the hood, read about rats in your car engine before you start the car again. And if the mice showed up as the nights got colder, the page on rodents in fall and winter explains why they come indoors at that time of year.

Yes. Once they are in the garage, mice and rats can follow wires and pipes into the house or squeeze through gaps in the wall the garage shares with your living space.

The ICWDM handbook chapter spells out the routes. Rodents travel along electrical lines and pipes, get through fire wall sheathing that was not sealed well, and slip in around furnace ducts, water heaters and laundry drains. If your water heater, furnace or washer hookup sits in the garage, several of those openings are in one spot.

Start here. Take a flashlight to the shared wall and look at each place a pipe, wire, duct or drain passes through it. Look for gaps around them, droppings along the base of the wall and fresh gnaw marks at the edges. Check the door into the house as well, since it needs the same tight seal at the bottom as an outside door.

Fit the overhead door with a rubber bottom seal that meets the floor all the way across, and put a rodent-proof sweep on the side door. Then check that no gap is left at the bottom corners.

The University of Kentucky extension recommends a rubber bottom seal for garage doors, noting that vinyl does a poor job of sealing once the weather turns cold. Use the same source's numbers as your test: 1/4 inch admits a mouse and 1/2 inch admits a rat. A quick way to find gaps is to close the door on a sunny day, switch off the garage lights and look for daylight along the bottom edge and at both corners.

For the walk-through door, NC State Extension draws a line between a rodent-proof door sweep and plain weather stripping. The rodent-proof kind seals tightly and has metal mesh packed inside. Weather stripping is a different product, so read the package before you buy.

A seal only helps when the door is shut. UC IPM's deer mouse guide says to keep the garage side door closed, above all after dark. That is the time of day deer mice and other rodents move around the most. A door propped open for a breeze on a summer evening undoes the rest of your work.

You can, as long as it goes into metal containers with lids that fit tightly. A bag of kibble or seed sitting on the floor is an easy meal for mice and rats.

NC State Extension notes that rats are heavy chewers that often gnaw through plastic to reach food, and it names metal containers with snug lids as the way to store these products. A plastic tote may keep dust out, but it will not hold up against a rat that keeps chewing. Scoop what you need, close the lid and pick up spilled food right away.

Seattle & King County's list also includes garbage and grease, such as the drippings on an outdoor grill. Keep trash cans in the garage lidded, and clean the grease tray before you roll the grill back inside.

Height and spacing count too. A University of Nebraska-Lincoln Extension guide on house mice advises keeping stored items at least 8 inches above the floor and at least 1 foot out from the walls. That makes the area less inviting to mice and makes it easier to inspect for them. Shelving set out from the wall does both jobs and gets boxes off the concrete.

Sealing keeps new rodents out, but it does nothing about the ones already living in the garage. Public Health Seattle & King County recommends the simple wooden snap trap for rodents inside a garage, shed or vehicle. Set traps where you find droppings or gnawing, and keep both traps and any bait where children and pets cannot reach them.

Cleanup carries its own risk. The Chelan-Douglas Health District in Washington says people can get hantavirus when virus particles float into the air and are breathed in, and it singles out cleaning garages, sheds, unused vehicles and other enclosed spaces where rodents have been.

So open the big door and let the garage air out before you start. Put on gloves and a respirator, and wet down droppings and old nests before you touch them. Leave the push broom and the shop vac on the wall, since both can kick dust into the air you breathe. For the full method, see how to clean rodent droppings safely.

Call a pro when mice keep turning up after you have sealed the doors, when you see signs inside the house, or when you cannot find how they are getting in. A big cleanup job in a garage that has been shut for months is another fair reason.

A pro starts with an inspection of the garage, its doors and the wall it shares with the house. That means checking door seals and corners for gaps, then following pipes, wires, ducts and drains to see where rodents could pass through. Trapping removes the animals already inside, and sealing closes the openings with materials that stand up to chewing.

Before any work starts, ask what the inspection covers, which openings will be sealed and with what, and whether return visits to check traps are part of the job. You can also ask whether the company is licensed.