What's the single most effective way to keep mice out?

Exclusion — sealing every opening ¼ inch or larger with materials mice can't chew through, per UNH and University of Missouri Extension. Missouri Extension calls this 'building them out' and considers it the most permanent form of mouse control available, more reliable than traps or repellents alone. The highest-yield spots to check first are the foundation, sill plate, utility penetrations, and door thresholds, since those are where most ¼-inch-plus gaps are found in practice.

What materials should I use to seal gaps against mice?

Steel wool packed tight and anchored with caulk, copper mesh in damp locations, or ¼-inch, 24-gauge hardware cloth for larger openings. Plastic sheeting, screen, wood, rubber, and other soft or gnawable materials are unsuitable on their own because mice chew through them. The material has to be harder than a mouse's teeth and installed without leaving a bitable edge, which is why professionals pack hard mesh into a gap and cap it with sealant rather than relying on foam alone.

Is cleaning up food enough on its own to keep mice out?

No. Sanitation reduces what draws mice, but mice need very little food to survive and can persist on crumbs even in a clean kitchen, so it can't substitute for physically sealing entry points. Extension guidance treats exclusion as the foundation of mouse control and sanitation as the necessary partner — do both, since a home that's food-secure but still has ¼-inch gaps is still an easy entry for mice.

Daniel Brady · NH-Licensed Pesticide Applicator · License #782664

|Reviewed by Daniel Brady

What Steps Prevent Mice From Entering a Home?

Depends on sealing every ¼-inch gap — sanitation alone won't do it

UNH Cooperative Extension puts it directly: the best way to start any mouse control effort is to keep mice from getting inside to begin with, sealing up all exterior cracks around the house and paying special attention to the foundation and where pipes and utilities enter the home. University of Missouri Extension calls this 'building them out' — eliminating every opening larger than ¼ inch is the most successful and permanent form of control. Materials matter: fill small gaps with steel wool anchored by caulk (or copper mesh in damp spots) and cover larger holes with ¼-inch, 24-gauge hardware cloth or sheet metal, since plastic, wood, and screen fail because mice chew through them. Sanitation supports exclusion but doesn't replace it: store food and pet food airtight, clean crumbs daily, and reduce outdoor harborage like woodpiles and dense vegetation.

At a Glance

Short answer: Seal every gap ¼ inch or larger with chew-proof materials; sanitation and harborage reduction support it.
Key fact: 'Building them out' — permanent exclusion — is the most successful mouse-control method, per extension guidance.
NH relevance: Finish mouse-proofing by late September, ahead of Manchester's first frost (~Oct 19 at 50%, ~Oct 29 at 80%).
Action needed: Inspect the foundation, utility penetrations, and door thresholds with a flashlight, then seal every ¼-inch gap found.

The honest answer

The short of it

The verdict

Depends on sealing every ¼-inch gap — sanitation alone won't do it

UNH Cooperative Extension puts it directly: the best way to start any mouse control effort is to keep them from getting inside to begin with, by sealing up all exterior cracks around the house, paying special attention to the foundation and where pipes and utilities enter the home. University of Missouri Extension calls this 'building them out' — eliminating every opening larger than ¼ inch is the most successful and permanent form of mouse control. Sanitation (airtight food storage, clean crumbs, secured garbage) supports exclusion, but because mice need so little food and water, sealing is the step that actually keeps them out.

Key Numbers

What Steps Prevent Mice From Entering a Home — By the Numbers

¼ inch

Smallest gap a mouse needs — the exclusion threshold

24-gauge

Hardware cloth spec recommended for mouse-proofing larger holes

Rule of thumb: if light shows under a door, mice can enter

Deep Dive

The full picture

UNH Cooperative Extension puts it directly: the best way to start any mouse control effort is to keep them from getting inside to begin with, sealing up all exterior cracks around the house and paying special attention to the foundation and where pipes and utilities enter the home. University of Missouri Extension calls this 'building them out' — the most successful and permanent form of mouse control is eliminating every opening larger than ¼ inch.

Materials and the exclusion checklist

Fill small gaps with steel wool anchored by caulk, or copper mesh in damp spots, and cover larger holes with ¼-inch, 24-gauge hardware cloth, sheet metal, or cement. Plastic sheeting or screen, wood, rubber, and other gnawable materials are unsuitable because mice chew through them. Doors are a chronically overlooked entry point — if daylight is visible underneath, add a rodent-resistant door sweep. Inspect the full perimeter with a flashlight: foundation, sill plate, utility penetrations, door thresholds, vents, and rooflines.

Sanitation and harborage support exclusion

Exclusion is the foundation, but mice are nibblers that need almost no food or water, so sanitation is the necessary partner: store all dry goods and pet food in airtight glass, metal, or hard-plastic containers, clean crumbs and spills daily, and secure garbage. Reduce outdoor harborage too — elevate woodpiles 12 inches off the ground, trim vegetation away from the foundation, and clear debris — so mice have less reason to congregate against the house in the first place.

Bottom line — Seal every gap ¼ inch or larger with chew-proof materials, finishing before the fall frost window, then back it up with airtight food storage and reduced outdoor harborage. Exclusion does the heavy lifting; sanitation keeps the pressure from building back up.

Ready to build mice out for good?

Anchor's licensed NH technicians find and seal every ¼-inch gap sanitation alone can't fix, ahead of the fall push indoors.

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Local Context

Why this matters in New Hampshire

With Manchester's first frost near October 19 at 50% probability and October 29 at 80% (NOAA 1991–2020), complete mouse-proofing by late September across the service area to beat the seasonal push indoors, then re-inspect each fall.

Key local data

Much of southern and central NH's older housing stock has fieldstone or rubble foundations and wood sill plates that give rodents ground-level entry (UNH Cooperative Extension exclusion guidance).

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Service Area Map

Southern New Hampshire

Common Questions

Frequently asked

Sources (4)

[1]
UNH Cooperative Extension — How Can I Get Rid of Mice in My House?(2024)
[2]
University of Missouri Extension — Controlling House Mice(2024)
[3]
CDC — Rodent Control: Seal Up, Trap Up, Clean Up(2024)
[4]
UC IPM — House Mouse (Home & Landscape)(2024)

Written & reviewed by

Verified

Daniel Brady

NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)

Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.

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Preventive Rodent Control

Exclusion First, Sanitation Second

Anchor Pest Services inspects the full perimeter and seals mouse-sized gaps across southern and central NH before the seasonal push indoors. Family-owned since 2017, NH license #782664.

Get a Free Preventive Rodent Inspection (603) 785-0118

Free inspection — no flat-price guesswork
NH-licensed applicators (#782664)
Seasonal preventive plans across southern & central NH

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Keep Exploring

What Steps Prevent Mice From Entering a Home?

The short of it

What Steps Prevent Mice From Entering a Home — By the Numbers

The full picture

Materials and the exclusion checklist

Sanitation and harborage support exclusion

Ready to build mice out for good?

Why this matters in New Hampshire

Frequently asked

Exclusion First, Sanitation Second

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