Mice Move Indoors When It Cools: How to Rodent-Proof Your Calgary Home Before Fall

The first cool nights of late August are when it starts. As temperatures drop, mice begin scouting Calgary neighbourhoods for a warm place to spend the winter — and your house is the top candidate. A mouse can squeeze through a gap the width of a pencil, and the average Calgary home has dozens of those gaps hiding in plain sight.

The good news: rodent-proofing is mostly a handyman job, not a pest-control job. Seal the entry points, and the mice never get in to begin with. Here's how to do it yourself, what to look for around a Calgary home, and when it's worth calling someone.

Why Calgary homes are an easy target in late summer

Alberta's long winters make indoor warmth irresistible to mice. When Calgary nights dip toward single digits in late August and September, mice in every neighbourhood — from Brentwood and Haysboro to Acadia and Falconridge — start pressing against foundations, siding, and door sweeps looking for a crack. Once inside, a single breeding pair can multiply fast through the winter, and the damage goes well beyond gnawed cereal boxes: chewed wiring is a real fire hazard.

Calgary's housing stock gives them plenty of routes in. Older inner-city homes in Inglewood, Bowness, and Mount Pleasant have settled foundations, worn door sweeps, and utility penetrations that have been open for decades. Newer communities like Mahogany and Nolan Hill aren't immune either — mice follow the same gaps around gas lines, vents, and garage doors.

Where mice actually get in: the entry-point checklist

You don't need to be an exterminator to spot the problem. Walk the outside of your Calgary home with this checklist and mark every opening, no matter how small:

• Garage door bottom seal. The rubber strip under the door wears out, and the gap at the corners is one of the top entry points in any Alberta garage.
• Door sweeps and thresholds. Front, back, and side doors lose their sweep over time. If you can see daylight under a closed door, a mouse can get through.
• Utility penetrations. Where the gas line, air conditioner lineset, cable, or internet enters the house — often loosely sealed with caulk that has cracked.
• Foundation vents and weeping holes. Small openings that need screens, not wide-open gaps.
• Siding and trim gaps. Corners and joins where vinyl or wood siding has pulled slightly away from the wall.
• Roofline and soffit gaps. Mice climb brick and stucco in Calgary surprisingly well; an open soffit corner is an open door.
• The crawlspace or rim joist. In older Calgary homes the rim joist area in the basement is a patchwork of small holes around pipes and wiring.

How to seal each entry point (the handyman way)

The principle is simple: mice can't chew through steel or properly applied sealant the way they can through foam or soft plastic. Here's what actually works, done the way a Calgary handyman would do it.

1. Seal small gaps with the right materials

For cracks up to about a quarter inch, a quality exterior-grade caulk or silicone does the job. For anything larger, back the gap with steel wool or copper mesh first, then seal over it with caulk or foam. The metal is what stops the teeth — mice will chew straight through plain spray foam and use it as bedding.

2. Replace worn door sweeps and garage seals

A new door sweep costs a few dollars and takes minutes, but it closes the most-used entry point in a Calgary home. For the garage, replace the bottom seal when it's cracked, curled, or no longer touching the floor at the corners — the two spots mice find first.

3. Screen vents and close utility penetrations

Cover foundation and soffit vents with metal mesh, and re-seal around gas lines and AC linesets where the old caulk has shrunk. This is also the moment to check the weeping holes in brick veneer — they need small screens or weep-hole covers, not solid caulk, so the wall can still drain.

4. Walk the foundation and siding

Use a caulking gun on cracks in the foundation and any gaps where siding has pulled loose. In Calgary, freeze-thaw cycles open these cracks wider every year, so a gap you sealed two years ago may be back.

5. Tidy the perimeter (it helps more than you'd think)

Mice hide in what's stacked against your house. Firewood, lumber, and dense shrubs against the foundation create covered runways straight to an entry point. Keep firewood off the ground and a few feet from the wall — standard advice across Alberta's colder regions.

DIY or call a Calgary handyman?

Most of this is weekend DIY. But there are times when calling YOFF is the smarter call:

• You have gaps you can't safely reach — high soffits, second-storey corners, or a steep roofline.
• The garage door seal is beyond a simple strip — a bent track or uneven floor means the seal will never sit right until it's fixed.
• You've sealed what you can see and still find signs of mice — the entry point is hidden, and a pro's eye finds it faster.
• You want the whole perimeter done properly in one visit before the weather turns.

Sealing entry points is handyman work — caulking, weatherstripping, door sweeps, mesh, and garage seals. No pest contract, no poison, just closing the door before the mice walk through it.

The bottom line

The window to rodent-proof a Calgary home is right now, in late August and early September, before the nights turn cold and the mice start moving in earnest. Walk the perimeter, find the gaps, seal them with steel and caulk, and you'll skip the scratching-in-the-walls season entirely. It's one of the cheapest forms of home insurance in Alberta — and it's a lot less trouble than a winter of traps and chewed wiring.

Want the whole perimeter sealed before fall? → Get in touch with YOFF