How Mice Get In: A Room-by-Room Guide to Sealing Your CNY Home

If you trap mice every fall and they keep coming back, the traps aren't the problem — the open entry points are. Trapping clears the mice inside today; sealing the gaps is what keeps the next wave out when cold weather pushes rodents toward your home's warmth. In Central New York's older housing stock, those gaps are everywhere if you know where to look.

The basement and foundation

Start here — it's where most mice enter. Look at the sill plate, the seam where the wooden framing sits on the stone or block foundation; decades-old homes often have gaps along its length. Check every utility penetration: water lines, gas lines, electrical conduit, and cable all pass through holes that are rarely sealed tightly. Fieldstone foundations, common in the region, are especially leaky.

Doors, garage, and ground level

Worn or missing door sweeps are an open invitation, especially on garage and basement doors. The gap under an overhead garage door is a frequent entry point, and the garage then connects to the house. Check where the garage meets the foundation and where any additions join the original structure.

The roofline and attic

Mice (and squirrels) climb. Gaps at the roofline, unscreened gable and soffit vents, and the junctions where dormers and additions meet the roof all provide access to the attic, which then connects down into the walls. Overhanging branches give rodents a highway to the roof.

Why professional exclusion lasts

Sealing mouse entry points properly isn't a matter of stuffing steel wool in a hole — mice defeat that. Durable exclusion uses materials like hardware cloth and sealed metal that stand up to gnawing and weather, installed across the whole building envelope. There's a bonus, too: the same gaps that let mice in let heated air out, so a thorough job tightens the house. Done right, exclusion ends the annual reinfestation instead of just pausing it.

The openings people miss

The obvious gaps get found. The ones that keep a house on an annual mouse cycle are usually less visible: the gap where the sill plate meets the foundation, especially on fieldstone; utility penetrations for water, gas, electric, cable, and dryer vents; the junction where an enclosed porch or addition ties into original construction; garage door corners and the bottom seal; and where siding terminates at grade.

On the older housing common in Ithaca, Cortland, and Elmira, there is rarely one hole. There are a dozen small ones, which is why a methodical pass around the building outperforms fixing whatever was found first.

Doing it in the right order

Sealing a building that already has mice inside without trapping first can leave animals shut in, which is unpleasant in the obvious way. The usual sequence is to trap down the interior population first, then seal, then verify.

Verification is worth naming as a step. Fresh droppings, gnawing at a sealed point, or continued activity after sealing generally means an opening was missed, not that sealing does not work. On an old house, one follow-up pass a few weeks later is normal and is part of doing the job properly rather than a sign it failed.