How Mice and Rats Actually Get In, and the Gaps Everyone Misses

The pencil test

A house mouse fits through a gap about six millimetres across, roughly the width of a pencil. A rat needs something closer to the size of a quarter. Neither number is intuitive, and it is why so many people are certain their house is sealed while rodents come and go nightly.

The gaps that get missed

Utility penetrations are the biggest offender: where the gas line, the air conditioning line set, the dryer vent or the cable enters the wall, there is usually a hole cut oversized and never properly closed. After that, the bottom corners of garage doors, where the rubber seal never quite meets the frame. Then weep holes in brickwork, gaps under siding at the foundation line, unscreened crawlspace vents, and the void where the deck ledger board meets the house.

Steel wool is not a repair

Stuffing a hole with steel wool slows a mouse down and nothing more. Rodents pull it out, and it rusts. Proper exclusion means hardware cloth or metal flashing fastened over the gap, sealed at the edges, with the surrounding timber repaired if it has been chewed. Expanding foam on its own is worse than useless, because rodents chew through it easily and it hides the evidence.

Trapping without sealing is a subscription

If you only trap, you will keep trapping. The population outside your house is effectively unlimited, and an open entry point is an advertisement. The order that works is: trap out what is inside, seal every way in, then verify that activity has stopped. Reverse those steps and you seal rodents into your walls.

Do the outside work before winter

The first properly cold week of the year produces a predictable spike in rodent calls. Sealing in early autumn is far easier than dealing with an established indoor population in January. If you would rather have someone else crawl the foundation line, call (833) 652-6912.

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