Why do I have mice in a clean house?

Updated 12 November 2026.

You wipe the counters, take out the garbage and keep food put away, and still you have mice. It is a common and upsetting experience, and it is not a sign that you did something wrong. This guide explains what actually draws mice into a tidy home and what to check.

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Why do I have mice in a clean house?

Mice come into clean houses because they need only three things: a way in, shelter and a small amount of food. A tidy kitchen does not stop mice from looking for warmth in fall and winter, and they can live on a few crumbs, pet food or birdseed. A gap the width of a dime is enough to let them in.

So if you have mice, the useful question is not whether the house is clean enough. It is where they are getting in, and what is drawing them to your property.

What attracts mice to a house?

In Ottawa homes, these are the draws we see most often:

• Cold weather. When nights drop toward freezing in the fall, mice move toward warm buildings. Many homes see the first signs from September to November.
• Gaps and cracks. Mice get in around pipes, cables, dryer vents, garage doors and the top of the foundation wall. See how mice get in.
• Food stored outside the house. Birdseed, grass seed, pet food and spilled seed under feeders are among the most common, especially in a garage.
• Garbage and compost with loose lids, or bins kept right beside a door.
• Clutter and cardboard. Boxes in a basement, garage or closet give mice material for nests and places to hide.
• Water. A slow leak under a sink or a damp basement gives mice a drinking source, which makes your home more comfortable for them.
• Hiding places outside. Firewood stacked against the house, dense shrubs and long grass against the foundation give cover.

I do not feed them. Why do they come anyway?

Because food is not the only reason. Shelter matters just as much, and a warm wall void or a quiet basement corner is ideal. A home that has had mice before often still has the gap they used, which is why signs can return.

Mice can live on very little. Crumbs behind the toaster, a few grains of cereal inside a drawer, pet food left out overnight or birdseed in the garage are enough to keep a few of them going, even in a home that looks spotless.

Where are they getting into a clean house?

Look first at ground level and at places where something enters the building:

• Where the gas line, air conditioner lines, outdoor tap, cable and internet lines go through the wall.
• The bottom corners of the garage door and the seal along the floor.
• The joint between the foundation and the siding, especially behind shrubs, decks and steps.
• Dryer and bathroom vents with a flap that no longer closes.
• Under exterior doors, if you can see daylight when you look from inside.

A pencil-wide gap is enough for a young mouse, and Health Canada says a mouse can squeeze through a crack about the width of a dime. Our winter mouse-proofing checklist takes you through every spot.

Do new builds and newer neighbourhoods get mice too?

Yes. Newer subdivisions are often built beside fields, ravines or open land, and construction disturbs mice that were already living there. In Kanata, Barrhaven and Orléans, mice often arrive from nearby land in the fall. Older homes have a different problem: more gaps in foundations and stone walls.

A new house is not mouse-proof. Gaps around utility lines and garage doors are common, and they can be sealed in the first year.

What should I do about it?

• Move food into hard containers, including pet food, birdseed and grass seed, especially in the garage.
• Close and move the garbage and compost away from doors, and use bins with tight lids.
• Cut back cover: move firewood away from the house, trim shrubs off the siding and clear long grass from the foundation.
• Reduce cardboard storage in basements and garages, or move boxes onto shelves and use plastic bins.
• Fix leaks under sinks and in the basement.
• Seal the gaps you can find with copper or stainless steel mesh and sealant, not foam alone. Do this once any mice inside have been dealt with.
• Check again after a week. New droppings in a cleaned spot mean mice are still using that route. Our guide to the signs of mice in the house shows how to tell old signs from new.

When cleaning is not enough

If you have done the above and still see droppings, hear scratching or find chewed packaging, the mice are established and at least one gap is open. That is when a professional inspection helps most. Our guide on DIY mouse control or an exterminator explains how to decide. For noises, see scratching in the walls at night.

How much does mouse control cost in Ottawa?

Our mouse and rat control is a flat $299 plus HST for houses, townhomes and condos. It includes a full inspection, locked bait stations placed away from children and pets, a photo report of the entry points we find, small gaps sealed with steel mesh on the first visit, a follow-up visit and a six-month guarantee. Larger sealing jobs are quoted separately as rodent proofing. See every price on the pricing page.

Quick answers about mice in a clean home

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Pick a day and time window on our booking page and tell us where you have seen signs. We inspect inside and out, treat with locked bait stations and show you the entry points we find. Have a question first? Read our pest control FAQ.

Book online See mouse & rat control ($299 + HST)

Not sure what you're dealing with? Call 343-341-2815 and describe it. We'll tell you what it is and what it costs.

Keep reading

• Signs of mice in your house
• How mice get in, and how to keep them out
• Winter mouse-proofing checklist for Ottawa homes

Sources

• Rats and mice, Health Canada

General information for homeowners. Every home is different; your technician will confirm what applies to yours.