Mice: steel wool, steel mesh and caulking

Where they get in

Rodents don't need an open door. According to Health Canada, mice can squeeze through cracks barely the size of a dime. For rats, a hole the size of a quarter is enough. So a crack you don't notice as you walk by can be a way in.

Health Canada names several weak spots: holes around pipes, dryer vents, attic vents, roof overhangs, cracks in the foundation and the bottom of doors. A worn door threshold is enough to let mice in.

Insects often follow the same paths. A crack that lets cold air in also lets in ants, spiders and other small visitors. Sealing these openings solves two problems at once: pests and drafts.

To this list, we add what we often see in the field:

• Where wires and ducts pass through the wall
• Around range hood and ventilation outlets
• The joint between the foundation and the siding
• Gaps around door and window frames

Signs of a visit

Mice are discreet, but they leave traces. Before looking for entry points, it helps to know where they travel in the house. Note the rooms where you find traces: the search starts near their exterior walls.

• Droppings along walls, under the sink or behind appliances
• Scratching in the walls or ceiling, especially at night
• Chewed food packaging or bags
• Gnaw marks on wires, wood or insulation

Steel wool, then caulking

Health Canada gives a simple method: fill holes around pipes with steel wool, then cover them with caulking or plaster.

Each material has its role. A rodent can chew through a sealant or foam. Metal blocks its way. The caulking on top holds the metal in place and closes the path for air and water. Together, they seal the opening for good.

Technique matters as much as material. The steel wool must fill the whole opening, packed tight, with no gaps at the sides. The caulking must then cover the metal and bond to the surface all around. A half-filled opening is still a way in.

For larger openings, we replace the wool with steel mesh cut to the size of the opening, then sealed. It's sturdier and cleaner. The mesh is fixed in the opening, and the specialized caulking covers it all the way around, with no loose edge.

Vents, thresholds and door bottoms

Some openings must stay open. A dryer vent, an attic vent or a ventilation outlet is there to let air and moisture out. Blocking them creates another problem. Health Canada recommends covering them with fine metal screening instead. Air gets through, mice don't. The same logic applies to roof overhangs.

These spots are often up high. If you have to climb a ladder or get on the roof to reach them, leave the job to a professional equipped to do it safely.

The bottom of doors is another classic entry point, especially for garage doors and side doors. Health Canada advises installing metal weatherstripping under doors. Foam or thin rubber weatherstripping can be chewed. Check the threshold too: if it's worn, cracked or loose, a mouse will find its way in even if the door closes well.

Mistakes to avoid

A few common habits give poor results. The first is plugging an opening with foam or sealant alone. A rodent can chew through it and reopen the path.

The second is closing off a ventilation outlet completely. You solve a mouse problem and create a moisture problem. Screening does both jobs at once.

The third is sealing the entry points while mice are still inside. They end up trapped in the house. If you see signs of them, deal with the rodents first with an exterminator, then close the access points.

Finally, don't wait for winter to do your walk-around. It's when the nights get colder, in the fall, that mice try to get in.

How we seal entry points

We don't do extermination. Our job is to close the entry points. If mice are already living in the house, an exterminator takes care of them. We make sure they don't come back.

We can also combine this work with caulking doors and windows. That way, we go around the house just once: joints around openings, weatherstripping and pest entry points.

• A walk around the house to find entry points
• Specialized pest-proofing caulking
• Installing steel mesh in openings
• Sealing holes and gaps
• Replacing worn weatherstripping, on request