The cardinal rule of mouse exclusion: seal every gap larger than 1/4 inch (the diameter of a pencil). Mice can collapse their skeleton to fit through any opening larger than this. Materials must resist chewing — foam and caulk alone are not sufficient as mice will chew through both.

Mice enter homes looking for food, warmth, and safety. The best way to stop them is to keep them from getting inside in the first place. This means paying attention to any small opening or source of food that might attract them. Here's everything you need to do, explained simply but in great detail.

Seal All Entry Points

Mice can squeeze through holes as small as a dime (about 1/4 inch). Check the entire outside of your house, especially near the foundation, around windows, doors, pipes, vents, and where cables come in.

• Use steel wool stuffed tightly into small holes, then cover with caulk. Mice can't chew through steel wool.
• For larger holes or gaps, use hardware cloth (a strong wire mesh), sheet metal, or cement to cover the area.
• Weather-strip doors and windows. Install door sweeps at the bottom of all exterior doors — make sure you don't see any light coming through when the door is closed.
• Fix or replace any damaged screens on doors, windows, and vents.
• Seal gaps around electrical wires, cables, and pipes with expanding foam. Inspect dryer vents and protect them with a screened cover.

Match the material to the gap size:

• Small gaps (under 1/2 inch) around pipes: stuff tightly with steel wool, then seal over with expanding foam or silicone caulk.
• Larger gaps (1/2 inch to 2 inches): hardware cloth (1/4 inch mesh) fixed with screws.
• Gaps in foundation or concrete: hydraulic cement or mortar — mice cannot chew through either.
• NEVER use regular foam alone — mice chew through it in minutes.

Eliminate Food Sources

Mice are always looking for something to eat. If they can't find food, they won't want to stay.

• Store all pantry foods like rice, pasta, cereal, pet food, and birdseed in metal, glass, or heavy plastic containers with tight lids. Never leave food in cardboard or thin plastic — mice can chew right through.
• Clean up crumbs and spills right away. Sweep and mop your kitchen regularly, especially under and behind appliances.
• Don't leave pet food out overnight. Pick up uneaten food and wash pet bowls daily.
• Take out the garbage regularly and use cans with tight-fitting lids.
• Compost bins should be sealed and kept well away from the house.

Reduce Clutter and Nesting Spots

Mice love places where they can hide and build nests.

• Keep closets, basements, attics, and garages as tidy as possible. Avoid piled-up boxes, paper, or clothes where mice can hide.
• Store items in plastic bins with secure lids instead of cardboard boxes.
• Keep firewood, brush, trash, and clutter at least 20 feet from your home's exterior.
• Trim shrubs, weeds, and grass near your house's foundation — mice use these as cover to sneak inside.

Maintain the Home's Exterior

A well-kept outside is your first defense.

• Fix broken vent covers, foundation cracks, missing siding, and rotted wood promptly.
• Install chimney caps and mesh over roof vents to stop mice from climbing in.
• Keep gutters clear so water doesn't pool and weaken building materials, which could create holes over time.

New Hampshire homes built before 1980 — especially those with stone or rubble foundations — have a significantly higher number of potential entry points than modern construction. If you live in an older NH home, a professional exclusion inspection is strongly recommended as a preventive measure, even without an active infestation.

Use Prevention Tools If Needed

If you've had problems with mice before, consider using extra tools to prevent them.

• Place mouse traps (even unbaited) along walls in basements, garages, and attics as an early warning system.
• Ultrasonic rodent repellents plug into outlets and emit noises unpleasant to mice (humans can't hear them). They're not foolproof, but they can help in combination with other steps.
• Consider professional pest control if you find lots of droppings or signs of damage — a pro can identify and close off hidden entry points you might miss.

Regularly Inspect for New Problems

Mice are persistent. Make it routine to:

• Walk around your house every few months and look for new gaps, gnawed spots, or droppings.
• Check attics, basements, garages, and under sinks for any sign of sneaky activity.
• Fix problems immediately — the sooner you act, the less likely mice will move in.

By following these steps, you'll make your home extremely unattractive and nearly impossible for mice to enter. The key is to stay consistent: keep things sealed, clean, and tidy, and be alert for any new signs of trouble.

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