Where Do Mice Enter Homes During the Fall and Winter?

When nights get colder in the Ottawa–Gatineau region, mice start looking for warm, sheltered places to spend the winter—and your home is at the top of the list. They squeeze through tiny gaps around the foundation, roofline, garage, and utilities, then spread through walls and ceilings. Understanding where they get in is the first step before you try any kind of mice removal or prevention.

Why mice target homes in fall and winter

In the fall, mice begin looking for shelter to spend the winter. In the Ottawa-Gatineau region, dropping temperatures, early frosts, and the arrival of snow make finding food more difficult. Homes become particularly attractive, as they offer more favorable conditions than the outdoors.

Once settled in, mice take advantage of the constant warmth, food supplies, and undisturbed areas—such as attics or spaces behind walls—to build their nests. Since they do not hibernate and can reproduce year-round, a subtle presence in the autumn can turn into a full-blown infestation during the winter.

The most common exterior entry points around your home

The most common places where mice enter homes are gaps along the foundation, under doors and garage doors, around utility lines and vents, and up at the roofline where the roof meets the walls. Mice also love sheltered spots under decks, porches, and exterior staircases, especially where snowbanks pile up and hide access points.

Foundation and ground-level gaps

Foundations and exterior walls near the ground sometimes have small openings that mice can use to enter the house. Pay particular attention to the following areas:

• Cracks in poured concrete or block foundations, especially near corners.
• Gaps where gas lines, cable, or air-conditioning lines enter the wall.
• Openings around basement windows.
• Damaged or missing mortar joints on brick homes, including around weep holes.

In winter, snow piled against the foundation can actually help mice: it gives them cover to explore cracks at the snowline that you cannot see from your driveway.

Doors, and garage doors

Check the ground-floor exterior doors, including garage and side entry doors:

• Worn or missing weatherstripping along the bottom of doors.
• Daylight showing under a garage door or side door.
• Warped frames or rotted door jambs, common in older central Ottawa homes.

A mouse can squeeze through an opening of about 6 mm—roughly the width of a pencil. Even a small gap under a door can therefore allow one to enter the house and settle in for the winter.

Vents, and building penetrations

Any place where something passes through a wall is a potential mouse entry point:

• Dryer vents, especially if the flap does not close tightly.
• Bathroom and kitchen exhaust vents with missing screens.
• Openings around electrical conduits or hose bibs.

Roofline, soffits, and upper levels

Mice can climb to the roof and enter through upper floors. Rough brick, stucco, wood siding, and even downspouts can act like ladders. Common upper-level entry points include:

• Gaps where soffits meet brick or siding.
• Open or unscreened roof vents and gable vents.
• Spaces around chimneys or skylights where flashing has pulled away.

Decks, porches, and exterior stairs

Spaces beneath outdoor structures can serve as shelters for mice, especially in the autumn. Sheltered from the wind and elements, they may settle there before seeking a way inside the house.

Be sure to inspect:

• Void spaces under wood decks or porches.
• Enclosed staircases leading to side or basement doors.
• Storage under exterior steps where debris accumulates.

These areas warrant special attention, as they can conceal openings where outdoor structures meet the house—particularly near the rim joist. This allows mice to gain access to the building without their presence being immediately apparent.

Hidden interior pathways

Once mice get into the structure, they rarely stay at the original entry point. They use wall cavities, ceiling voids, and utility chases to travel between food, water, and nesting areas. That is why you might hear scratching in a bedroom ceiling even though the actual entry was a gap behind a garage or deck.

Attics and ceiling voids

Attics are a favourite winter nesting site because they are relatively warm and undisturbed. Common signs of mice in attics include:

• Soft scratching or scurrying sounds, especially at night.
• Small dark droppings on top of insulation or near hatch doors.
• Runways or trails pressed into the surface of loose-fill insulation.

From the attic, mice can drop down inside wall cavities, following plumbing stacks or electrical runs to kitchens and bathrooms.

Walls, utility chases, and basements

Mice love the protected corridors created by framing and mechanical systems. Typical interior pathways include:

• Gaps around plumbing pipes under kitchen and bathroom sinks.
• Openings where furnace ducts or HRV lines pass through framing.
• Cracks along basement sill plates and band joists.

If you find droppings under a sink or behind a stove, it usually means there is a broader interior network at play—not just one random visitor.

Is professional intervention necessary?

The location where you spot or hear mice does not always reveal their entry points. For instance, you might catch several in the kitchen without noticing the opening near the foundation that allows them to access the house.

This highlights the challenge of relying solely on traps: while they may temporarily reduce the mouse population, they do not prevent new mice from entering the building. Furthermore, some entry points are difficult to detect without a thorough inspection—particularly those located behind exterior structures or in hard-to-reach areas.

Hiring a mice removal specialist like Aspen Wildlife Control allows you to address the problem at its source. Rather than focusing only on visible mice, the team examines potential entry points, identifies signs of activity, and determines the measures needed to secure the building. This approach targets easily overlooked openings, reduces the risk of recurring infestations, and protects your home from rodent-related damage.

The goal, therefore, is not merely to remove the mice currently present, but also to prevent them from returning through the same entry points.

 

FAQ’s

How small a gap do mice need to enter a home?

Mice can squeeze through an opening of about 6 to 7 millimeters—roughly the diameter of a pencil. Consequently, even a small crack in the foundation or a gap around a pipe can allow them to enter. To prevent intrusions, these openings must be sealed with rodent-resistant materials.

What are the most common mouse entry points in a house?

Mice can enter through cracks in the foundation, gaps around pipes and cables, poorly sealed basement windows, or openings beneath exterior doors and garage doors. Damaged vents, soffits, and roof junctions also provide potential entry points.

The spaces beneath patios and porches also warrant special attention. They offer mice sheltered areas where they can explore hidden openings at the junction of the foundation and the house structure.

How do mice get into upper-floor apartments or townhouses during winter?

Mice can reach upper floors by climbing certain exterior surfaces or by traveling along pipes and downspouts. In townhouses and apartment buildings, they also move through shared walls and connecting attics, passing through small gaps around pipes. Since the entry point may be located in a neighboring unit, an inspection of access points and shared spaces may be necessary.

What can I safely do myself before calling a mice removal company?

You can inspect for suspected mouse entry points, replace worn weatherstripping, and keep food and waste in sealed containers. Avoid using poisons that are accessible to children or pets, and do not seal off entry points without first checking whether mice are already inside. Mice removal company can then identify entry points, remove any rodents present, and implement measures to prevent their return.

When should you hire a company for mice removal in Ottawa-Gatineau?

If you regularly hear scratching sounds in the walls or ceilings, find droppings in several rooms, or suspect an infestation in the attic, it is best to act quickly. Aspen Wildlife Control can inspect your home, locate entry points, and implement tailored mouse removal and exclusion solutions. Early intervention helps minimize damage, contamination risks, and recurring infestations.