Warehouse Rodent Control in Ontario: Where Rodents Get In

Quick answer

Rodents get into commercial buildings through a short, predictable list of openings: the gaps at the top and sides of roll-up door tracks, worn dock seals and dock levellers, personnel doors with more than a quarter-inch under them, unsealed pipe and conduit penetrations, floor drains with worn grates, and roof-level vents and utility chases. A mouse only needs an opening larger than about a quarter of an inch. Bait boxes around the outside of the building do not stop any of this — they count rodents, they do not exclude them. The fix is a documented exclusion pass on the building shell, done with metal and concrete rather than foam and weatherstripping, plus a weekly walk so that new gaps get found in days instead of seasons. Where there is already an active population inside, sealing comes after treatment and verification, not before.

Every November the same call comes in from facility managers across the GTA, Peel and Simcoe County: droppings on a pallet rack, a gnawed carton in receiving, something moving behind the compactor. Nothing about the building changed. What changed is outside it — outdoor food and cover collapsed with the first hard frosts, and a heated building with a loading dock is the most hospitable structure in an industrial park. A warehouse offers what a house cannot: constant warmth, uninterrupted horizontal runs along conduit and pallet racking, cardboard in volume, and a door that stands wide open part of every working day.

This is the part of the problem a facility manager actually controls — not the rodent population in the ditch behind the property, but the shell of the building and how disciplined you are about it.

The one measurement that governs everything

Before the inspection list, the number that makes the list make sense.

The University of California’s integrated pest management program, in its house mouse guidance revised in July 2025, states that house mice “can squeeze under gaps ¼ inch tall, and through openings 3/8 inch wide,” and sets the exclusion standard as eliminating “all gaps and openings larger than ¼ inch.” The University of Nebraska–Lincoln’s rodent-proof construction handbook puts the same threshold at any opening larger than ¼ inch (0.6 cm) for mice, and larger than ½ inch (1.3 cm) for rats.

Peel Region’s rat prevention guide for industrial, commercial and institutional facilities — prepared for the Region by urban rodentologist Robert M. Corrigan — makes the point in plainer language for rats: “It requires a hole the size of a quarter to allow a rat entry beneath a door or through a hole in the wall.”

A quarter of an inch is less than the thickness of a pencil. That is the standard your building is measured against, and it is why “the door looks closed” is not an inspection finding. On commercial sites across Mississauga and the rest of the Peel industrial belt — tilt-up construction, multiple dock positions, shared waste compounds — the number of openings meeting that description on one building is routinely in the dozens.

Where rodents actually get in

Overhead and roll-up doors

This is the first place to look and the one most often misread. The problem usually is not the gap at the bottom when the door is down — it is the vertical channel. The Nebraska handbook notes that rats and mice “can easily climb up the space between the door and the inner wall or track to the top,” which turns the door assembly into a ladder to an opening nobody inspects at eye level. Its recommended fix is to close the gap at the top or sides of roll-up doors with conveyor belt material shaped to fit the side channel frames.

Check the top of the door curtain and the side channels from inside, with the door closed, with a light behind it.

Dock levellers, dock seals and the pit

Dock levellers sit over an open pit. The pit is warm, dark, protected, and connected to the building. Perimeter dock seals and bumpers are rubber, and rubber is a consumable in this context, not a barrier: the Nebraska handbook is blunt that “rubber or vinyl weather stops are quickly gnawed through.” A torn dock seal on a trailer position used twenty times a day is an open door with a flap over it.

Personnel doors and thresholds

The specification is tight: the Nebraska handbook calls for the distance between the bottom of the door and the threshold not to exceed ¼ inch (0.6 cm), and for flashing to extend to within ⅛ inch (0.3 cm) of the door edge at the sides and bottom. It also recommends metal channel or flashing on the lower edge of doors, particularly softwood doors, because the alternative is that the door becomes the entry point.

And the correction most sites need to hear, from the Peel guide: “Weather stripping a door will not rodent-proof a door.” Weatherstripping is an air seal. It is not a rodent barrier and it was never designed to be one.

Pipe, conduit and sprinkler penetrations

Every service that enters the building is a hole that was drilled oversized on purpose. Sprinkler mains, electrical conduit, gas, water, compressed air, refrigeration lines, data. The Nebraska handbook’s method is to close openings around pipes and cables where they enter structures with Portland cement mortar, and to back holes three inches or more in diameter with ¼-inch hardware cloth. The Peel guide is explicit about the shortcut that fails: “Spraying canned foam or merely stuffing a wad of stainless steel into a hole is not sufficient.”

Floor drains

Routinely missed, and a direct route in. The specification is simple: metal grates held firmly in place, with grate openings not exceeding ¼ inch (0.6 cm). Walk your drains and look at the grates, not just the covers.

Roof level

Mice can, in the Nebraska handbook’s wording, “climb almost any rough vertical surface, such as wood, brick, concrete, weathered sheet metal, and many plastic products.” UC IPM agrees: they “are excellent climbers and can run up any rough vertical surface.” On a commercial roof that means unscreened intake and exhaust vents, gaps at curb flashing, and open utility chases where a rooftop unit was added and the penetration never properly closed. Vents can be screened behind the grill with ¼-inch hardware cloth.

The exterior is doing half the work against you

A perfectly sealed building in a badly kept yard still gets pressure on it every night, and pressure finds the one gap you missed.

The Peel guide’s exterior guidance for ICI sites is specific. On waste: bins and lids clean and tightly closed, collection not delayed for days, and the space under a compactor kept clean because it collects food fragments. On frequency it warns that “once-a-week cleanups will not necessarily prevent rats.” On grounds: keep shrubs and landscaping from growing thick enough to form low “caves,” keep the yard clear of junk piles and old equipment, and keep stored materials in sheds elevated off the floor by about 40 to 45 cm.

Two distances from that guide are worth writing on the wall: rats generally nest within about a 30 m radius of a food source, and untidy waste areas are usually found within roughly 50 to 75 m of where rats are being seen. If staff report sightings at one end of the property, the harbourage is close — and findable.

Materials: what holds and what does not

The pattern across all three sources is consistent: metal and concrete hold, gnawable materials do not.

UC IPM states that “plastic screening, rubber, vinyl, insulating (expanding) foam, wood, and other gnawable materials are ineffective” for plugging holes used by house mice, and directs that openings around pipes, vents and cables be sealed “with metal or concrete.” The Nebraska handbook adds that “neoprene seals, spray-in-place foam, and similar products commonly used to close openings are not rodent-proof,” and gives working specifications: woven 19-gauge, ½- x ½-inch mesh to exclude rats; 24-gauge, ¼- x ¼-inch mesh to exclude mice; galvanized sheet metal at 24 gauge or heavier for wall and pipe barriers, 22 gauge or heavier for kick plates and door edging.

Both sources treat steel wool as a temporary plug only, and both note it rusts. Foam has one legitimate role — filler behind or over hardware cloth that is doing the actual work — and none as the barrier itself. Which material belongs in a residential wall void is a separate question covered elsewhere on this site; on a commercial shell the answer is almost always metal, mortar or mesh.

Why the bait boxes around your building are not a plan

Most commercial sites in Ontario already have a ring of exterior bait stations and a service sticker on the electrical room door. That programme is doing something — measuring pressure and intercepting some of it. What it is not doing is keeping rodents out of the building. The Peel guide says it directly: exterior bait boxes “will not prevent rodents from invading,” and good housekeeping matters more. If your rodent programme consists entirely of boxes checked on a route, you have monitoring without exclusion — useful, but not control.

Sequence matters, and it differs by situation

If the shell has no active interior population — nothing in the catch records, no fresh droppings, no gnaw damage — exclusion is straightforward preventive work. Seal it, properly, now.

If there is already an active population inside, sealing first is the wrong move, and it is the most common error we are called in to undo: closing the exits traps a live population in the wall voids and ceiling spaces of a building you then have to work inside. Our method runs the other way — treat and station on day one, leave the exit routes open by design so rodents leave the structure and die outside it, verify at about three weeks, and only then seal every entry point. That order is what keeps a dead-rodent problem out of the ceiling grid above a production line. It is never a single visit, and it is never sealing on day one.

The weekly walk

The Peel guide’s recommendation for ICI facilities is that “property managers or business owners should perform weekly inspections,” covering foundations, doors, grounds, burrows and waste handling. It is a recommendation rather than a legal requirement, but it is the highest-value habit available to a facility and it takes about fifteen minutes.

Walk the perimeter and look for fresh burrow openings at the foundation line. Stand inside each dock position with the door closed and look for light. Put a hand on every dock seal. Check the threshold gap at every personnel door. Look at the floor drains. Open the waste compound and look under the compactor. Note what you find, with a date, in the same log your pest provider signs — that log is what turns a vague “we keep seeing mice” into a work order a contractor can scope.

What a commercial programme should actually include

Four things: a documented inspection of the shell with every gap identified by location, exclusion work specified in materials that hold, a treatment and verification sequence matched to whether there is an active interior population, and a service record good enough to show an auditor or an insurer.

Sani IQ is licensed under the Ontario Pesticides Act and registered with the Ministry of the Environment, Conservation and Parks, and our technicians are employed, licensed and background-checked rather than subcontracted. Where product is required we work from reduced-risk materials and the lightest intervention that will hold. Inspection is credited when you book.

FAQ

How do I know whether rodents are getting in, rather than just living outside? Interior evidence is the test: droppings along wall-floor junctions and on top of pallet racking, gnaw damage on cartons or wiring, smudge marks on conduit runs, or captures in interior devices. Exterior burrows and yard sightings tell you about pressure; interior evidence tells you the shell has failed.

We had the whole building sealed last year. Why are they back? Buildings move and get used. Dock seals tear, thresholds wear, a rooftop unit gets installed and its penetration never gets closed properly, a trade drills a conduit hole and foams it. Exclusion is not a one-time capital project — it is a sealed condition that has to be maintained, which is the reason for the weekly walk.

How long does it take to get a facility clean? Where there is an active interior population, plan on treatment and station placement on day one, a verification visit at about three weeks, and sealing after that verification. Exclusion scope on a larger building may run across more than one visit depending on how many openings the inspection finds. No one should be promising you a single visit.

Who is responsible for exclusion in a leased industrial unit — us or the landlord? It depends on how the lease allocates responsibility for the building shell versus the interior, so get the clause read before the work is scoped. In practice the inspection findings settle the conversation, because they identify each gap by location and whether it is structural.

---

Rodent pressure on an Ontario commercial building peaks between now and February, and the gaps that let it in are findable in an afternoon. To have the shell of your building assessed properly, start with our commercial pest elimination programme, or answer a few questions through our free quote quiz and we will come back with the right scope for your site. For background on the species doing most of the structural damage on commercial sites, see our pest library entry on the Norway rat.