Table of Contents
Trapping mice already in the attic is the easy part – see how to get rid of mice in the attic for that. Getting them out and having more move in two weeks later is the frustrating part. Attics are ideal mouse habitat: warm, dark, undisturbed, and full of cardboard and insulation for nesting. These seven steps cut off the access routes and remove the welcome mat. Do them in order – step one matters more than the other six combined.
1. Seal entry points with foam, steel wool, or cement
This one isn’t negotiable. You can trap every mouse in your attic today and three more will show up tomorrow if you leave the door open.
Mice get through openings the size of a dime (about 6 mm). Check along the roofline, where utilities enter the house, around vents and pipes, and anywhere two different building materials meet. Pay close attention to soffits and eaves – those gaps are often an inch wide and completely ignored.
For small gaps, pack tightly with steel wool first, then seal over it with expanding foam. Foam alone won’t hold because mice chew right through it. Steel wool they won’t bother with. For larger holes, cut a piece of hardware cloth (1/4-inch wire mesh), screw it in place, then seal the edges with cement or caulk.
Do this before anything else. There is no point in any other prevention step if mice can still walk in through your roofline.
2. Add a chimney cap and close the fireplace damper
An uncapped chimney is an open door. Mice, squirrels, and birds all use them. They don’t necessarily climb down into the fireplace – they drop into the attic from the flue collar or find a gap in the chimney surround.
A metal chimney cap with mesh screening costs under $50 at any hardware store and takes 30 minutes to install. It also keeps rain out. There is no argument for not having one.
If you have a fireplace, keep the damper closed when it’s not in use. Mice can climb up through the firebox just as easily as they come down from the roof.
3. Trim vegetation away from house
Overhanging tree branches are a bypass. Mice are good climbers but they’d rather run along a branch than cross open ground where predators can spot them. Any branch that touches or overhangs the roof gives them direct access to your roofline, bypassing whatever ground-level deterrents you’ve set up.
Trim branches so nothing is within 4 feet (1.2 m) of the structure. Focus on anything that overhangs the roof, eaves, or upper-story windows. While you’re at it, clear leaf litter from the gutters – packed debris at the roofline is exactly where mice look for a foothold.
Shrubs pressed against the foundation are the same problem at ground level. Keep a clear gap between foundation plantings and the house.
4. Move firewood away from foundation
A woodpile against the house is a mouse condo. They nest in the gaps between logs, breed there through spring and summer, and when the temperature drops they follow the warmth into your walls through gaps you didn’t know existed.
Stack firewood at least 30 feet (9 m) from exterior walls and get it off the ground on a rack or pallets. Elevated storage cuts down on nesting and keeps the wood dryer anyway.
Check each log before bringing it inside. Mice hitch rides in on firewood more often than people realize. Same rule applies to lumber piles and construction material stacked near the foundation. If it’s against your house, move it.
5. Store attic items in sealed plastic bins
Cardboard boxes are mouse housing. They chew through the walls for nesting material, nest inside the boxes, and use the stacks as cover while moving around. An attic full of cardboard is functional mouse habitat.
Replace them with hard plastic bins with tight-fitting lids. Brand doesn’t matter – Rubbermaid, Sterilite, whatever seals properly. Fabric items, old clothes, and holiday decorations are especially attractive for nesting; get those into sealed bins first.
An attic with plastic bins and clear floor space gives mice nowhere to hide and nothing to nest in. It also makes fresh droppings a lot easier to spot.
6. Clean up pet food immediately
Don’t leave bowls down when pets aren’t actively eating. Mice will work around a sleeping dog to reach a bowl of kibble left out overnight. Pick up bowls after meals, store opened bags in hard-sided sealed containers, and sweep up any spilled kibble.
For outdoor pets, bring food bowls inside at night. An outdoor feeding station after dark is a guaranteed draw.
Birdseed and wild animal feed are equally attractive – often more so, since they’re usually stored in the bags they came in, inside a shed or garage with gaps. Move them to metal garbage cans with tight lids. A reliable food source near your house gives mice strong incentive to find the entry points you missed. Take away the food and most of that motivation disappears.
7. Don’t count on ultrasonic repellers
Ultrasonic repellers are what people buy instead of sealing, and the research doesn’t back them. UC IPM is flat about it: high-frequency electronic devices aren’t effective, and there’s little evidence that sound, magnetic, or vibrational devices of any kind drive out established house mice or provide any prevention or control. The ultrasonic sound is directional, doesn’t carry behind objects, and loses intensity fast with distance – so even where it reaches a mouse at all, it isn’t doing much.
That makes them a poor substitute for the work on this page. If the entry points are already sealed and you want to plug one in near a wall where you’ve seen activity, there’s no harm in trying it. But don’t expect the device to do what steel wool and hardware cloth do, and don’t keep paying for it if fresh droppings keep appearing.
Seal the house first. That is the strategy, not the repeller.
