How do mice get into my house?
Mice can squeeze through any gap the size of a dime (about ¼ inch) — and your house almost certainly has dozens of them. The most common entry points are the gap between the garage door frame and the foundation, utility penetrations (where pipes and wires enter), dryer vents, and weep holes in brick. Traps catch what's inside; exclusion seals the door.
A single mouse inside usually means there are more — and they're using the same 3–5 entry points repeatedly. Finding and sealing those gaps is the permanent fix. Traps alone are a treadmill.
Where mice are actually getting in
Garage door frame gap
$20–$60 DIY / included in exclusion serviceWhat It Looks LikeGap between the door frame / weatherstripping and the foundation or floor — often visible as daylight from inside
Why Mice Use ItReplace the door bottom sweep and corner seals; add a threshold seal if the gap persists
Utility penetrations (pipes, conduit, cables)
$15–$40 DIY / included in exclusion serviceWhat It Looks LikeGap around any pipe or wire entering through the foundation or exterior wall — check under sinks, behind the dryer, at the water meter
Why Mice Use ItPack with steel wool and seal with expanding foam rated for rodents (standard foam is chewable)
Dryer and bathroom exhaust vents
$15–$50 DIY / included in exclusion serviceWhat It Looks LikeVent flap stays partially open or the flap is missing; gnaw marks around the vent collar
Why Mice Use ItInstall a rodent-proof vent cover with a tight-closing flap ($15–$30 at hardware stores)
Weep holes and foundation cracks
$20–$50 DIY / included in exclusion serviceWhat It Looks LikeVisible gaps at the base of brick veneer (weep holes are intentional — every 3–4 bricks); any crack wider than ¼ inch in the foundation
Why Mice Use ItFill weep holes with copper mesh inserts (steel wool works but rusts); seal cracks with hydraulic cement or polyurethane caulk
Gaps under doors (non-garage)
$10–$25 DIY / included in exclusion serviceWhat It Looks LikeDaylight visible under entry door or crawl space access door; door sweeps cracked or missing
Why Mice Use ItInstall or replace door sweeps — this is one of the cheapest and most effective exclusion steps
Roof and attic access
$50–$200 DIY / $300–$600 pro exclusionWhat It Looks LikeGaps at the roofline, around fascia boards, where pipes exit the roof, or where HVAC lines enter the attic; squirrel-size openings let mice in easily
Why Mice Use ItHardware cloth (¼-inch mesh) over any opening at the roofline; caulk small gaps; check gable vents for torn screens
Start here: the entry-point audit
- Walk the perimeter of your foundation at dusk with a flashlight — look for any gap larger than ¼ inch (dime-sized). Pay special attention to corners, where the garage meets the house, and anywhere utilities enter.
- Check under every sink and behind every appliance that has a water or gas line — these utility penetrations are consistently the #1 missed entry point.
- Look for rub marks (dark greasy smudges) along baseboards and walls — mice follow the same paths repeatedly and leave grease trails at entry points and travel routes.
- Snap traps along active runways (against walls, behind appliances) confirm you have mice and start reducing the population while you identify and seal entries. Victor snap traps with peanut butter work as well as anything.
Unlock the hiring checklist
Use this before you call a pest control, so you know what to ask and what to avoid.
Call a pro when…
- You're finding droppings in multiple rooms — a widespread infestation is beyond a trap-and-patch DIY job
- You've sealed the obvious gaps and traps keep catching new mice — there's a hidden entry you haven't found
- You hear activity in the walls or ceiling, not just under cabinets — mice in wall voids are harder to eliminate and can chew wiring
- You find a nest with pups — the population is established and actively reproducing
- The infestation is in a crawl space or attic — these require PPE (hantavirus risk from droppings) and are best handled by a licensed pest control company
Repair or replace?
For mice, the equivalent of repair vs. replace is traps-only vs. a full exclusion program. Traps alone cost almost nothing but never end the problem — new mice find the same entries. A professional exclusion program runs $300–$1,200 depending on house size and entry complexity, and it seals the house so you're not trapping indefinitely. If you've been buying traps for more than two seasons, the exclusion math almost always wins.
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Related questions
How small a gap can a mouse fit through?
A mouse can compress its skeleton to fit through any opening roughly ¼ inch wide — about the diameter of a pencil or the edge of a dime. If its head fits, its body follows. This is why visual inspection plus a smoke pencil (or even a candle near suspected gaps) is the only reliable way to find every entry.
Why do I suddenly have mice?
Most mouse invasions happen in fall — temperatures drop and mice start actively seeking shelter. A new construction project nearby, changes to landscaping (woodpile close to the house, overgrown shrubs), or a neighbor treating their own infestation can also push mice toward your house. The entry points were almost always there before; the mice just found them.
Does having one mouse mean I have more?
Almost always yes. Mice are social and leave scent trails that lead other mice through the same entry points. A single sighting — especially during the day — usually means the colony is large enough that they're competing for space and resources, which pushes the bolder ones into visibility.
What's the difference between mice and rats in the walls?
Mouse sounds are light and fast — rapid scurrying, often at night. Rat sounds are heavier and slower. Mouse droppings are ⅛–¼ inch, pointed at both ends; rat droppings are ½–¾ inch with blunt ends. The fix is the same (exclusion + trapping) but rat exclusion is more intensive — rats need a ½-inch gap or larger, which actually makes them slightly easier to block.