How mice enter Quebec homes during winter

When temperatures drop below 10 °C, thousands of mice actively seek warm shelter across Greater Montreal. An adult mouse can fit through a hole the size of a pencil — about 6 mm. That's tiny, and it's everywhere in a typical home.

Most common entry points

First hot spot: openings for gas, water and electrical lines crossing the foundation. Original sealing cracks over time. Second: garage doors, especially lower corners where the seal wears. Third: dryer and kitchen exhaust vents, especially if flappers no longer close properly.

Early signs

Before seeing a mouse, you'll notice droppings — small rice-grain black grains in drawers, under the sink, behind the stove. You may also hear scratching at night, especially in the ceiling or hollow walls. A strong urine smell in a closed closet is another indicator.

Why cleaning isn't enough

You often hear that mice "look for dirt." It's false. They look for warmth, water and an entry point. A spotless new house can be infested if the foundation has a crack or a conduit isn't sealed. Building tightness is what matters, not cleanliness.

The classic mistake: traps alone

Buying ten mouse traps at the hardware store and placing them around is an approach that kills a few individuals but doesn't stop the flow. While you catch two, ten more enter. Without professional sealing of entry points, the problem returns next year.

The two-phase approach

Professional intervention always happens in two phases: first elimination of the existing population (secured bait stations, strategic traps), then exclusion diagnosis — meticulous exterior inspection, precise identification and marking of every opening over 6 mm. You leave with a detailed report and the exact materials list (steel wool, mortar, specialized caulking) — you seal them yourself or with your contractor. That elimination + diagnosis duo is what prevents return.