Where the rat you saw actually came from
The first thought, when you see a rat near your home, is the sewer. Sometimes that is right. Often it is not. The City of Montreal's rodent control page sets out two distinct routes.
The first runs through the network. Rats come up when sewers or drains are damaged, and during excavation work that opens the street. In that case the problem sits in the line connecting your building to the collector, not in your kitchen.
The second runs through the building. An unused plumbing opening, a broken pipe, a crack wider than 15 mm is enough. That route has nothing to do with roadwork, and it stays open year-round.
The distinction matters because the fix is not the same. Sealing a crack solves nothing if the line under the slab is broken, and a camera inspection of the sewer is wasted if the rat walks in through an open vent shaft.
What construction changes, and what it does not
A worksite does not create rats. It relocates the ones already living nearby. When an excavation opens the ground, burrows and shelters disappear at once and the animals spread toward neighbouring buildings. That is why a street with no history of problems can produce several reports within weeks.
The trend is documented city-wide. According to Radio-Canada reporting (in French), 311 logged more than 1,700 rat-related calls in 2024, up from roughly 1,000 two years earlier, with Ville-Marie and Villeray-Saint-Michel-Parc-Extension leading. The same report notes that a 2023 motion calling for a city rat control plan, including how rats are managed during sewer work, was never acted on.
What that means for you: if a worksite is opening on your street, the time to close up your building is before it starts, not after the first sighting.
Rodents are not only a nuisance. Montreal's regional public health authority lists rodents among the unwanted animals that determine whether a dwelling is fit to live in, alongside cockroaches and bed bugs.
The openings a rat uses to get inside
An adult Norway rat gets through an opening of roughly two and a half centimetres. It gnaws to widen, it climbs, it swims. The points worth checking, in the order they usually turn up.
- Floor drains and basement drains with a jammed or missing backflow valve.
- Plumbing stacks capped off during a renovation and never properly sealed, which the City lists explicitly.
- Foundation cracks wider than 15 mm, especially around service entries.
- Garage door thresholds and basement windows with rusted-out screening.
- Private sewer access covers that no longer seat properly.
Find out how they are getting in
An inspection covers inside and outside, and identifies the route before anything is treated. From $99, with a written guarantee.
What the City handles, and what it leaves to you
The split surprises people. For a problem in a public space, a park or an alley, you call 311. For a food establishment, you contact food inspection. But for a private home, the City states the owner must call a qualified exterminator and carry out the necessary corrections.
The City works on its own property. It will not treat your basement. A tenant reports to the landlord without delay, and the landlord arranges the work. We covered that split, and the available recourse, in our article on who pays the exterminator in Quebec.
Telling a rat from a mouse
Getting this wrong costs weeks, because the treatment differs. The reliable markers.
- Droppings. Rat droppings run one to two centimetres. Mouse droppings are the size of a grain of rice.
- Burrows. Rats dig, usually against a foundation, under a deck or a shed. Mice do not.
- Sound. Rats move along the floor and low walls, mice in ceilings and upper partitions.
- Grease marks. A dark, polished trail along a baseboard or pipe means a heavy animal using the same route repeatedly.
If you are still unsure, our article on the signs that separate rats from mice goes further.
When to call an exterminator, and what they do
Three things, in this order. Find the route, remove the animals, close the route. Skipping the third is the usual mistake, and the population rebuilds through the same opening within weeks.
Retail baits raise a specific problem with rats. An animal that dies inside a wall cavity or under a slab produces an odour that lasts weeks and draws flies. That is one reason a professional job pairs control with sealing rather than relying on poison alone.
The point to call is when one of these applies. You see a live rat indoors in daylight, which means an established population. You find one to two centimetre droppings in more than one room. You hear movement in low walls or under the floor. Or you have set traps and the problem continues, which means the way in is still open.
That is what our rodent control service in Montreal covers, where inspection, treatment and sealing are part of the same job.
Before cleaning up droppings, do not sweep and do not vacuum. Read the precautions public health actually recommends first: the instinctive move is exactly the wrong one.
Treat and seal in one job
Removing rodents without closing the access points does not hold. At Axion, sealing is part of the work.
Common questions
Does a rat in the alley mean I have rats indoors?
No. An alley already offers food and shelter, and a rat can live there without entering any building. What should concern you are the indoor signs: droppings, noises, grease trails or gnawed packaging.
Will the City exterminate my basement?
No. The City states that the owner of a private home must call a qualified exterminator and carry out the necessary corrections. The 311 line is for problems in public spaces, parks and alleys.
Should I wait until the roadwork on my street is finished?
No, the opposite. Excavation scatters the animals toward nearby buildings. Closing your access points before or during the work avoids treating an established infestation afterward.
Do rats always come from the sewers?
No. The City describes both routes: rats coming up through damaged sewers or drains, and rats entering through the building itself, such as unused plumbing or a crack wider than 15 mm. An inspection tells you which one applies to your property.