How to Keep Mice Out of Your House This Fall

The way to keep mice out of your house is exclusion: find and seal every gap about 1/4 inch or larger on the outside of the house before nights turn cold, using materials mice cannot chew, then remove the food and shelter that draw them to your foundation in the first place. House mice can squeeze through an opening roughly the size of a dime, so the job is mostly about detail: door bottoms, garage door corners, utility penetrations, vents, and the gap where siding meets the foundation. September and October are the time to do it, as mice start looking for warm shelter. This checklist walks you around the house from the ground up.

Part of our Pest Control guide →

In this guide

1. How Mice Get Into Houses
2. Choose the Right Materials
3. Fall Exclusion Checklist
4. Yard Habits That Invite Mice
5. Sheds, Garages and Garden Storage
6. Keep It Mouse-Proof Year-Round
7. What About Repellents?
8. Signs Mice Are Already Inside
9. When to Call a Pro
10. Frequently Asked Questions

How Mice Get Into Houses

Mice are excellent climbers and jumpers, can run along wires and pipes, and squeeze through openings far smaller than their bodies look. They tend to follow edges, so they find the gaps along foundations, under doors and around pipes. The most common entry points are:

• Gaps under exterior doors and at the corners of garage doors
• Holes where utility lines, AC refrigerant lines, cable and gas pipes enter the house
• Dryer, bathroom and kitchen exhaust vents without proper covers
• Foundation and crawlspace vents with torn or missing screens
• The joint between the foundation and the sill plate or siding
• Weep holes in brick veneer and gaps in damaged mortar
• Gable vents, soffits, roof returns and gaps where gutters meet the roofline
• Openings around window AC units and basement windows

Once they are inside walls, mice travel easily between floors. If you are already hearing scratching, see our guide on getting rid of mice in walls first, then come back to seal the house. Sealing a house with mice still inside can trap them where you do not want them.

Choose the Right Materials

Material	Use it for	Notes
Copper mesh	Stuffing gaps around pipes and wires	Does not rust like steel wool; pack tightly and seal over it
Steel wool	Small gaps indoors or protected areas	Rusts outdoors; cover with sealant
1/4 inch galvanized hardware cloth	Vents, crawlspace openings, larger holes	Fasten with screws and washers or staples; cut edges are sharp
Exterior sealant or caulk	Sealing over mesh, small cracks	Mice chew it alone; always back with metal
Pest-block expanding foam	Large irregular voids with mesh packed in	Standard foam is chewed; mesh is what stops mice
Metal flashing or sheet metal	Chewed corners, door frames, large holes	Durable; can be painted
Mortar or concrete patch	Foundation cracks, masonry gaps	Permanent fix for masonry
Door sweeps and garage seals	Bottom of doors	Choose models with a rigid or brush insert

Fall Exclusion Checklist

Pick a dry day, grab a flashlight, a pencil to test gap sizes, and a notebook. Walk the outside of the house slowly, then repeat inside in the basement, crawlspace, garage and attic.

1. Doors

• Close each exterior door and look for daylight underneath and at the corners. Install a door sweep where you see light.
• Replace worn thresholds and weatherstripping.
• Check the door between the garage and house; it should seal as tightly as a front door.
• For garage doors, replace the cracked bottom rubber seal and add a seal or brush strip to the sides. The bottom corners, where the seal meets the jamb, are a favorite entry point.

2. Foundation and siding

• Look along the line where siding or the sill plate meets the foundation. Seal gaps with copper mesh and exterior sealant.
• Patch foundation cracks with mortar or concrete patch.
• Leave brick weep holes open for drainage, but fit them with purpose-made weep vent covers rather than stuffing them solid.
• Check where decks, porches and steps attach; gaps behind them are easy to miss.

3. Pipes, wires and lines

• Inspect every place a hose bib, gas line, AC line, cable, phone or electrical conduit enters the house.
• Pack openings with copper mesh, then seal with exterior sealant or a pest-block foam.
• Repeat indoors, especially under sinks, behind appliances and around water heaters and furnaces where pipes come through floors and walls.

4. Vents

• Fit dryer vents with a rodent-resistant cover that still opens freely; never fully screen a dryer vent, since lint buildup is a fire risk.
• Check bathroom and kitchen exhaust vent flaps close fully.
• Cover foundation and crawlspace vents with 1/4 inch hardware cloth.
• Inspect gable and soffit vents; replace torn screens with hardware cloth.

5. Roofline and attic

• Look at roof returns, fascia gaps and where gutters meet the roof. Mice climb siding, downspouts and vines to reach them.
• Seal gaps with metal flashing or hardware cloth.
• Check that chimney caps and plumbing vent boots are intact.

6. Windows and inside the garage

• Repair torn window screens and seal gaps around window AC units.
• Check basement window wells and frames.
• Inside the garage, seal gaps around the wall that adjoins the house and around utility penetrations.

Yard Habits That Invite Mice

Mice that live comfortably near your house will keep probing for a way in. Make the area around the foundation less attractive:

• Stack firewood at least 20 feet from the house and off the ground on a rack.
• Keep shrubs and groundcovers trimmed back from the siding, and avoid dense ivy against the foundation.
• A strip of gravel 12 to 18 inches wide along the foundation discourages burrowing and nesting better than thick mulch.
• Clean up spilled bird seed, or move bird feeders away from the house and use trays that catch spills.
• Feed pets indoors, and store pet food, bird seed and grass seed in metal or heavy plastic bins with tight lids.
• Keep trash and recycling in lidded bins, and rinse food containers.
• Use enclosed compost bins and do not add meat, dairy or cooked food.
• Remove clutter and stored cardboard boxes from the garage floor, where mice nest unseen.

The same idea, removing food and shelter while blocking access, works for other garden pests too. Our guides to keeping squirrels out of the garden and keeping rabbits out of the garden apply it outdoors.

Sheds, Garages and Garden Storage

Outbuildings often host the mouse population that eventually moves into the house. Garden sheds full of seed packets, bulbs, grass seed and fertilizer bags are ideal nesting sites. Store anything edible, including bird seed, flower bulbs and vegetable seed, in sealed metal cans or heavy bins with locking lids. Lift stored items onto shelves so you can see the floor, and sweep it out each season. Check shed doors for gaps at the bottom and corners just as you would on the house, and screen any vents with 1/4 inch hardware cloth.

In the garden, pull back thick mulch from the base of the house each fall, harvest or clear fallen fruit and vegetables, and avoid piling brush or leaves against the foundation over winter. Raised beds and compost bins placed near the house should have hardware cloth bottoms and tight lids if mice are a problem.

Keep It Mouse-Proof Year-Round

• Spring: check for winter damage to door sweeps, garage seals and siding; trim back shrubs as they leaf out.
• Summer: inspect new utility work, such as cable or AC installs, and seal any new holes the installers left.
• Early fall: do the full exclusion walk-around and move firewood into place away from the house.
• Winter: keep a couple of snap traps set in the garage and basement as an early warning system, and check them weekly.

What About Repellents?

Peppermint oil, mothballs, dryer sheets and ultrasonic plug-ins are popular, but evidence that they keep mice out over the long term is weak, and mothballs are a health hazard used indoors. They are no substitute for sealing gaps. Cats can help in some homes but do not stop entry. Save your money for copper mesh, hardware cloth and door sweeps.

Signs Mice Are Already Inside

• Droppings about the size of a grain of rice, often along walls, in drawers or under sinks
• Gnaw marks on food packaging, baseboards or wiring
• Shredded paper, insulation or fabric in hidden corners
• Scratching sounds in walls or ceilings, especially at night
• A musky odor in closed cabinets or closets

Not sure whether you have mice or rats? Droppings and damage size differ; our guide to mice vs rats explains how to tell. If mice are already inside, set snap traps along walls where you see droppings, baited with a small amount of peanut butter, and keep sealing entry points as you trap. Our roundup of the best mouse traps compares snap, electronic and live-catch styles. Wear gloves and wet droppings with a disinfectant before cleaning them up; do not sweep or vacuum them dry.

When to Call a Pro

Call a pest control company if you keep catching mice after sealing, hear activity in multiple areas, find gnawed wiring, or cannot reach roofline and attic gaps safely. Many companies offer exclusion services, where they seal the house and set traps, along with follow-up visits. Our guide to mouse exterminator cost explains how these services are typically priced, and our pest control guide covers prevention for other common household and garden pests.