How to Keep Mice Out of Your Garage: Sealing, Storage and Safe Removal

TL;DR

• Seal every gap larger than 1/4 inch (about 6 mm), starting with the garage door. Mice can squeeze through cracks as small as a dime (Health Canada).
• Mice already inside? It is usually best to trap them first, then seal once the catches stop, so you don't lock them in.
• Replace any door seal that is torn, flattened or no longer touches the door, and plug other gaps with materials mice usually can't chew: steel wool, metal flashing or cement, not foam or wood.
• Do it in late summer or early fall, before cold nights tend to push mice indoors, and don't leave the garage door open for long periods, never overnight.
• Store pet food, birdseed and grass seed in metal or glass containers if you can, and swap cardboard boxes for bins with tight lids.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

Figuring out how to keep mice out of your garage usually starts with an uncomfortable discovery: the door you close every night is not sealing much. The rubber gasket along the bottom cracks and warps as it ages, the side seals rarely meet the frame in the corners, and any strip of daylight under the door is a way in.

Sealing is only half the job, though. Mice already living behind the storage shelves have to be trapped first, or a fresh door seal simply locks them in with the birdseed, the cardboard boxes and your car's wiring.

Garage mice also follow a calendar. The same cold nights that send you looking for a jacket push them toward the nearest sheltered building, and a garage is often the closest one.

Why Do Mice Get Into Your Garage?

Mice get into your garage because it gives them shelter from the cold, food and nesting material behind a door that rarely seals tightly. To a mouse, a garage is a warm, quiet storage room with almost no traffic at night, which is exactly when mice are active.

Cold Weather

Cold weather is the main trigger. According to UC IPM, house mice frequently move into buildings in autumn, when nighttime temperatures drop, and Health Canada notes that deer mice invade buildings near fields and woodlands in the fall. In Canada, that makes late summer and early fall the time to get your garage ready.

Food Sources

Food sources in a garage are often better than outside: bags of dog or cat food, birdseed, grass seed, and garbage bins waiting for collection day. Mice can also find water there, from leaks or snow melting off your car.

Nesting Material

Nesting material is everywhere in a typical garage. Mice build nests from finely shredded paper or other fibres (UC IPM), so cardboard boxes, old rags, insulation and stored cushions all make good bedding. UC IPM lists garages among the places to search for nests.

Attached Garages

Attached garages can be a direct route into your home. A mouse that gets into the garage can follow pipes, wires and gaps in the shared wall into the house or up toward the attic. That is why sealing the garage is part of keeping mice out of your house and closing off the usual ways mice get into your house.

What Are the Signs of Mice in Your Garage?

Mice in your garage leave droppings, gnaw marks and shredded nesting material, usually along walls and near stored food. Mice are active at night, so you are more likely to find these clues than the mice themselves.

Mouse Droppings

Mouse droppings are the clearest sign. They are typically about 3 to 6 mm long, dark, and shaped like small grains of rice, and you will usually find them along walls, on shelves and near pet food or birdseed.

Gnaw Marks

Gnaw marks show up on food bags, cardboard boxes, plastic bins and the rubber seal at the bottom of the garage door. Chewed corners on the door seal are a sign mice are coming in right there.

Nests

Nests look like loose balls of shredded paper, fabric or insulation. Check behind boxes, inside drawers, under workbenches and in stored items you have not moved in months.

Musky Odour

A musky odour is commonly associated with mice, according to UC IPM. A stale, urine-like smell in a closed garage usually means mice have been there for a while.

Chewed Car Wiring

Chewed car wiring is the most expensive sign. UC IPM warns that house mice can damage vehicles by gnawing on electrical wires, and a car parked in a garage with mice may be an easy target. If you find droppings or nesting material under the hood, read our guide to mice in your car before driving.

How to Keep Mice Out of Your Garage by Sealing Entry Points

Keeping mice out of your garage depends on sealing every gap larger than 1/4 inch (about 6 mm), starting with the garage door. Health Canada says mice can squeeze through cracks as small as a dime, and UC IPM notes they can slip under gaps 1/4 inch tall. If mice are already inside, trap them before you seal, so you do not lock them in.

The Daylight Test

The daylight test is the fastest way to find gaps. On a sunny day, close the garage door and the lights, then look along the bottom of the door, the corners and the side door: every spot where light gets in is a spot a mouse can use. At night, you can do the reverse with a flashlight from outside while someone watches from inside. For a full checklist, see how to find mice entry points.

The Garage Door Bottom Seal

The garage door bottom seal is the most common entry point. Health Canada warns that even the small gaps from worn thresholds under doors let mice in. Rubber seals tend to crack and warp with age, and one pest control company recommends replacing rubber garage door thresholds every few years. Choose a seal that follows the contours of your floor and is long enough to leave no opening at the edges.

Garage Door Side Seals

Garage door side seals are the second weak spot, especially at the corners where they meet the bottom seal. Side gaskets get old and brittle and rarely seal well in the corners, and mice may chew a hole through rubber big enough to squeeze through. Replace any seal that is torn, flattened or no longer touches the door.

Metal Rodent Guards

Metal rodent guards add a layer mice cannot chew. Mice gnaw through wood, plastic and rubber, but metal reinforcements usually stop them. Products sold for this include stainless steel strips that stick inside the side seals and rubber bottom seals lined with stainless steel mesh. Buyer reviews are mixed: some say the adhesive does not hold or that mice chewed the trim beside the guard, so check them after installing.

The Side Door

The side door needs the same attention as the big door. Health Canada recommends metal weather stripping under doors, and UC IPM suggests covering the edges of doors with metal where mice gnaw. Make sure the door fits tightly in its frame.

The Door Into the House

The door into the house is your last line of defence. Fit it with a tight door sweep, and seal any gaps where pipes and wires pass through the shared wall between the garage and the house.

Foundation and Wall Gaps

Foundation and wall gaps let mice in even when the doors are perfect. Look for cracks in the concrete, gaps where the slab meets the walls and openings around water pipes, vents and utility cables. UC IPM recommends sealing these, for example with metal or concrete.

Sealing Materials

Sealing materials must be ones mice cannot chew. UC IPM and the Public Health Agency of Canada recommend wire screening, coarse steel wool, metal flashing or cement. Steel wool makes a good plug but may rust over time, so pack it in firmly and cover it with caulk or patching compound. Plastic, rubber, vinyl, expanding foam and wood are not enough on their own, because mice gnaw right through them.

Keeping the Garage Door Closed

Keeping the garage door closed matters as much as the seals. Avoid leaving it open for long periods, and never overnight, since that is when mice usually move around.

When to Seal Your Garage

The best time to seal your garage is late summer or early fall, before cold nights push mice indoors. Check the seals again in spring, and replace any that winter has cracked or flattened. If you also store a camper or trailer, our guide to keeping mice out of an RV covers it.

How Do You Make Your Garage Less Attractive to Mice?

Making your garage less attractive to mice means removing the food, garbage and hiding spots that let them settle. UC IPM notes that cleaning and decluttering will seldom remove mice on their own, but mice cannot survive in large numbers without places to hide and nest.

Food Storage

Food storage is the first fix. Health Canada recommends storing dry food and dry pet food in metal or glass containers, since mice may chew through plastic bins and bags. Do the same with birdseed and grass seed.

Garbage

Garbage should go in containers with tight-fitting lids. Metal cans are the safest, and loose garbage bags stacked on the garage floor are an open invitation.

Storage Bins Instead of Cardboard

Storage bins with tight lids beat cardboard boxes, which mice often shred for nests. Move holiday decorations, clothes and paper into sealed bins, and put anything soft, like cushions or blankets, in bins too.

Clutter

Clutter gives mice cover. Health Canada advises removing cosy nesting sites in unused clutter around your house and garage. Use shelving to keep items off the floor and away from the walls, so you can see droppings and sweep easily.

Firewood

Firewood is a favourite hiding place. Health Canada recommends raising woodpiles about 30 centimetres (1 foot) off the ground, and the Public Health Agency of Canada advises moving woodpiles away from buildings. Keep only a small amount of firewood in the garage.

The Area Around the Garage

The area around the garage can draw mice right to the door. Cut tall grass and weeds, trim plants growing against the walls, and keep compost bins and bird feeders away from the building.

Do Repellents Keep Mice Out of a Garage?

Repellents do not keep mice out of a garage on their own. University extension experts and Health Canada agree that sealing and storage generally do more than any smell or sound.

Peppermint Oil

Peppermint oil is the most popular home remedy, but the evidence is weak. Ask Extension (University of New Hampshire) says repellents overall, including essential oils, have not shown to be very effective, as their scent tends to fade quickly. Cotton balls soaked in peppermint are unlikely to stop a mouse from walking under a worn seal.

Ultrasonic Repellers

Ultrasonic repellers have very limited use, according to UC IPM: the sound is directional, does not reach behind boxes and shelves, and mice can get used to it. Health Canada notes that mice may adapt to these devices and return. If you still want to compare models, see our review of the best mouse repellers.

Mothballs

Mothballs are not a mouse repellent. They are pesticides labelled for clothes moths in airtight spaces, and using them against mice goes against the label and has little or no effect. Their vapours can also cause headaches, nausea and eye and nose irritation in a closed garage.

Cats

Cats catch some mice, but UC IPM says there are few situations where cats or dogs control a mouse population. A cat is not a substitute for sealing the garage.

How Do You Get Rid of Mice Already in Your Garage?

Getting rid of mice in your garage is usually a trapping job: UC IPM generally recommends trapping in garages and homes where only a few mice are present. Trap first, then seal the entry points once the catches stop.

Snap Traps

Snap traps are the simplest and most effective tool. Health Canada says snap traps and electronic traps are easy to use and very effective if they are well positioned and set properly. See how to set a mouse trap for the steps, and our picks for the best mouse trap.

Trap Placement

Trap placement decides how fast you catch them. Set traps close to walls, behind objects and in dark corners where you see droppings, at a right angle to the wall with the trigger end closest to it. Health Canada suggests 1 trap per metre along walls, and UC IPM recommends spacing traps no more than about 10 feet (about 3 metres) apart. Check traps daily, and keep them out of reach of children and pets.

Bait

Bait works best when it is strong-smelling and sticky. Health Canada suggests peanut butter, bacon grease mixed with oats, raisins or gumdrops. Use a small amount pressed onto the trigger, so the mouse cannot lick it off without setting off the trap.

Glue Traps

Glue traps are a poor choice. UC IPM notes that adult mice may sometimes avoid the glue, and garage dust and cold can make glue boards lose their grip. The US Centers for Disease Control and Prevention also advises against them, and UC IPM notes that captured mice defecate as they struggle, which increases the potential for contacting hantavirus.

Live Traps

Live traps catch mice without killing them, but releasing mice elsewhere does not work. UC IPM says mice moved some distance away may find their way back.

Poison Bait Stations

Poison bait stations are a last resort in a garage, where pets, children and wildlife pass through. Consumer (domestic class) rodenticides should only be used in tamper-proof bait stations, as the Government of British Columbia advises, and domestic products containing brodifacoum, bromadiolone or difethialone are prohibited in Canada, according to Health Canada's Pest Management Regulatory Agency. Always look for a PCP number on the label and follow it exactly. Poisoned mice can also die in walls or under stored items and cause odours.

Cleaning Up Droppings Safely

Cleaning up droppings safely protects you from hantavirus, which NC State Extension says is spread most commonly through contact with deer mice. Open the garage door and windows and stay out for at least 30 minutes, as Alberta advises. Then follow the Public Health Agency of Canada steps:

1. Wear rubber or plastic gloves, and an N95 respirator in a confined space.
2. Do not sweep or vacuum droppings, because that stirs up dust.
3. Spray droppings and nests with a Health Canada-approved disinfectant or 1 part bleach to 9 parts water.
4. Let it soak for 10 minutes, then wipe up with paper towels.
5. Double-bag the waste and put it in the garbage according to local by-laws.

Our guide to cleaning mouse droppings covers each step in detail.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when traps keep catching mice and new signs keep appearing, when mice have reached the house or the car, or when you cannot find where they get in. A licensed technician can inspect the garage, remove the mice, seal entry points with chew-proof materials and come back for follow-up checks. You can get a quote from a recommended local exterminator through Pest Agent's referral form. For other mouse topics, visit the mice hub.