Mice in the garage: how to get them out and keep them out
Updated 19 September 2026 · 8 min read
Published by CAVE4MAN — storage, workshop and man-cave kit for UK home garages. The shop is not open yet.
Mice are in your garage because they can get in and there is something to eat or nest in. Seal the gaps under and around the doors and around pipes, get bird seed, pet food and cardboard into sealed containers off the floor, and clear the clutter they hide in. Traps deal with the ones already inside.
Why the garage, and why now
Mice come into a garage for the same two reasons they come into anything: it is warmer and drier than outside, and there is something to eat or nest in. The first cold nights of autumn push them in, which is why the droppings appear in October. A garage is easier than a house because the door has a gap under it and nobody sits in the garage at night to notice.
What they are eating is usually not what you would think. Bird seed is the big one, then pet food, grass seed and lawn feed, the bag of compost, and anything in the car. What they nest in is cardboard, old carpet, rags, insulation offcuts and the paper you keep meaning to recycle. A garage with a sack of sunflower hearts on the floor and a stack of boxes in the corner is a mouse hotel with the sign lit.
The signs are droppings, small and dark, along the base of walls and on shelves; gnawed corners on packets; a shredded nest of paper or fabric in a box or a drawer; a smell; and a dog or cat suddenly very interested in one corner. Mice run along edges, so look along the base of the walls first, and behind whatever is against them.
Find how they are getting in
Exclusion is the whole game. Trapping mice that can walk back in is a hobby, not a solution. The usual rule of thumb is that a mouse gets through any gap it can fit its head into, which for a young one is about the width of a pencil, so the search is for small gaps, not holes. In a garage the candidates are predictable.
The bottom of the up-and-over door is first: the rubber seal is worn, or the corners were never sealed, or the floor is uneven and the door sits on the high point. Then the side door, which usually has daylight under it. Then the air bricks, whose grilles break or were never there. Then wherever a pipe or cable comes through the wall, gaps under the fascia and at the eaves, cracks in the blockwork, and the gap between a door frame and the brick.
- 1Go in during the day with the lights offEvery point of daylight at floor level or in a wall is a candidate. Mark each one with tape before you start sealing.
- 2Check the door seals by feelRun a hand along the bottom of both doors from inside. Where you feel a draught, a mouse can get through.
- 3Look for the runsMice follow the same routes and leave smear marks and droppings along them. The run leads to the hole.
- 4Check the outside faceWalk the outside at ground level: pipe entries, air bricks, damaged pointing, gaps under cladding.
Sealing: what works on which gap
Not every filler works, because mice chew. Expanding foam on its own is chewed through in a night; they treat it as bedding. The standard answer for small holes is coarse wire wool or steel mesh packed tightly into the gap, then mortar, filler or sealant over it to hold it in place. The wire is what stops them; the filler is what stops the wire falling out. On bigger gaps use metal mesh fixed over the opening, and mortar for masonry.
The door seals matter most, and they also fix the draughts the heating and condensation guides ask you to fix, so they pay twice. A rubber bottom seal on an up-and-over door has to touch the floor along its whole length; on an uneven slab that can mean a threshold strip fixed to the concrete to give it something flat to meet. Check it with the door shut from inside, looking for daylight.
| Gap | What works | What does not |
|---|---|---|
| Under the up-and-over door | New rubber bottom seal, brush strip, a threshold strip screwed to the slab | Foam, or a draught excluder that lifts with the door |
| Under the side door | A new door seal or a metal threshold, and fix the frame gap | A rubber sausage that gets pushed aside |
| Around pipes and cables | Wire wool or steel mesh packed in, then sealed over | Foam or sealant alone |
| Air bricks | Fine steel mesh over the outside, keeping the airflow | Blocking it, which starts a condensation problem |
| Cracks and holes in blockwork | Mortar, with mesh in larger holes | Filler, which they chew |
| Eaves and fascia gaps | Mesh or eaves comb | Foam alone |
Remove what they came for
Sealing the building and leaving the bird seed on the floor is half a job. Everything edible goes into a rigid, lidded container: metal or hard plastic, because a mouse goes through a paper sack and a bag-for-life without slowing down. That includes bird food, pet food, grass seed, fertiliser, the emergency biscuits in the car and the dog treats in the cupboard.
Then the nesting material. Cardboard boxes become lidded plastic crates. Rags and old towels go in a lidded bin or out. Insulation offcuts get used or thrown. Old carpet on the floor is a nest with a roof; get rid of it. And clear the floor along the walls, because that is where mice travel and where they hide: freestanding shelving lifts everything off the slab so you can see the whole floor edge, and hooks get the long things off the floor and onto the wall.
The car deserves a mention. A car that sits for weeks in a garage with mice in it becomes a nest, in the engine bay, the air filter box or the cabin. Chewed wiring is a genuinely expensive result of a cheap problem. Drive it regularly, keep food out of it, and if it is stored for winter, check under the bonnet every couple of weeks.
Dealing with the ones already inside
Once the building is sealed and the food is gone, the mice inside are a finite number and traps deal with them. Snap traps along the base of the walls, trigger side to the wall, baited with something they have to work at, peanut butter or chocolate spread rather than cheese. Several at once, not one. Check them every day. Live-catch traps are a choice you can make, but they need checking within hours, not days, because a trapped mouse dies quickly of stress and cold, and a mouse released at the end of the garden is back inside by the weekend.
This guide does not cover poison. It is a risk to pets, children and wildlife, and a poisoned mouse that dies inside a wall or under a floor smells for weeks. If the numbers are beyond a few traps, or they keep coming back after you have sealed everything you can find, that is what a professional pest controller is for, and they will find the entry point you missed.
Clean up with gloves and a mask, and do not dry-sweep the droppings, because the dust can carry disease. Spray them with disinfectant, wait, wipe, and bag it. Then keep the floor edges clear and the food sealed, and the garage stays boring to a mouse, which is the aim. Check the door seals again each autumn, because the seal that kept them out this year is a year more worn by the next.
Common questions
- How are mice getting into my garage?
- Almost always under the up-and-over door, where the rubber seal is worn or the corners were never sealed, or under the side door. After that: broken air-brick grilles, gaps where pipes and cables enter, cracks in blockwork and gaps at the eaves. Go in by day with the lights off and look for daylight at floor level; a mouse only needs a pencil-width gap.
- Will mice chew through expanding foam?
- Yes, easily, and they use the shreds as bedding. Foam on its own is not a mouse-proof seal. Pack the gap with coarse wire wool or steel mesh first, which they will not chew through, then mortar, filler or sealant over the top to hold it in place. On larger openings, fix metal mesh over them.
- What attracts mice to a garage?
- Food and shelter. Bird seed is the commonest food source, then pet food, grass seed and anything edible left in the car. For nesting they want cardboard, rags, old carpet and insulation offcuts, and a cluttered floor along the walls to hide in. Sealed rigid containers for food and lidded crates instead of boxes remove most of the attraction.
- Do mice nest in cars in the garage?
- Yes, especially a car that sits for weeks. They get into the engine bay, the air filter box and the cabin, nest there, and chew wiring, which is expensive. Drive it regularly, keep food out of it, and if it is laid up over winter, look under the bonnet every couple of weeks and deal with the garage's mouse problem rather than the car's.