Exterior Rodent Bait Station

Case Study: Rats Crawl Into Basement Walls in Old Toronto

The following case study describes the removal of a prolonged infestation of rats within the Casa Loma area. Rats that were burrowing outside had made their way into a family’s home by taking advantage of its structural vulnerabilities. With continued investigation and treatment, The Exterminators team was able to address the root causes of the issue and stop the pests from getting inside the house. A comprehensive treatment on both the interior and exterior of the home, along with a thorough exclusion of the premises has since left this Casa Loma house pest-free and should protect it for years to come.

Initial Inspection and Recommendations

The owners of the property reached out to The Exterminators after hearing scratching sounds coming from their son’s bedroom wall. The bedroom was located in the basement and the sounds could be heard at night, disturbing the son’s sleep. Hearing these sounds in the walls at night is a common symptom of a rat infestation, so rats were suspected to be burrowing in the wall. A technician promptly arrived on the scene to investigate.
During this first visit, the technician performed a thorough inspection of the home’s exterior and the bedroom inside. The home had a large deck in the backyard and an alley separating the property from the neighbours next-door. Wall vents were exposed on the side of the house facing the alley. Inside, rat droppings were found behind the drywall of the son’s bedroom. This could be observed by removing an access panel from the wall. Rats were burrowing into the walls of the house, but no direct entry point was found during the initial inspection. The technician thus recommended covering the wall vents outside to stop any pests from crawling through them and installing baits and traps on both the inside and outside of the home to begin the extermination process.

Initial Measures Taken

To suppress the rat population outside, the technician placed 3 bait stations along the home’s exterior walls. Bait stations consist of tamper-proof, plastic containers of rodenticide with holes on their sides for rats to enter. The rodenticides inside are specifically formulated to appeal to rats. After a few ingestions, rats begin to feel ill and retreat into their burrows to perish. This is the most effective way to get rid of rats outside and can only be serviced by a professional pest remover.
Inside, the technician set snap traps along the walls of the son’s bedroom. Snap traps are used indoors because they can be cleaned up immediately once a rat has been trapped. Using rodenticides indoors may result in there being dead rats in the walls, which will cause a stench. Cleaning this up is particularly difficult when there are walls in the way.

Initial Exclusion and Follow-up

A few weeks later, the customer agreed to exclude the wall vents. A technician then returned and covered the wall vents outside with a galvanized steel mesh. This material is strong enough to withstand the chewing and tearing of pests and is rust-proof so that it is not damaged by rain or snow. The gaps within the mesh are too narrow for mice to fit, yet wide enough to preserve the flow of air.

Wall Vent Cover Toronto
Rats and mice can climb walls and enter the home through the wall vents. Covering them with mesh keeps pests out.

Following the exclusion of the wall vents, the technician suspected that a pipe on the side of the house was responsible for letting the rats in. He then installed a one-way door to this entrance. The one-way door consists of a mesh tube with a flap inside it that swings outward, letting the animals out but blocking their re-entry. The door would simply let the rats out of the house when they wanted to venture outdoors and stop them from getting back inside. The evicted rats would then feed on the rodenticides outside.

Rat One Way Door in Side of House
One-way doors are highly effective at getting pests out of the home. Once out, they are forced to find another place to live.

During this second visit, the technician on site inspected the bait stations the previous technician had installed and found that the bait was nearly all gone. This proved that there were many rats living outdoors. The technician then refilled the stations and advised the homeowner to give the one-way door a few weeks to let the rats leave the house.

Exterior Rodent Bait Station
Bait stations are not only useful for keeping rats under control but for monitoring their level of activity. Here, all the bait was consumed within a few weeks, indicating a severe infestation.

Unfortunately, because the one-way door was in the alley, it was later crushed by a car. A member of The Exterminators team, however, quickly returned to fix the door. At The Exterminators, we provide warranties on all of our exclusion – if there is an accident or an animal breaks it during the warranty period, we will return and fix the problem at no additional cost.

Rat One Way Door Replaced Toronto
If a one-way door or piece of exclusion is accidentally broken, we will fix it. The one-way door in this case was replaced to continue to let the rats out.

Over the next few months, the property was re-inspected for rat activity and the bait stations were replenished. Rodent activity decreased and the sounds were no longer being heard in the basement bedroom walls. The one-way door was then removed and replaced with galvanized steel mesh.

Rat One Way Door Replaced with Mesh
The one-way door was replaced with mesh as soon as it was removed to ensure that no more rats would get in.

Rodent Return and Additional Exclusion

A few days after the door was removed, the homeowners of this Casa Loma property were hearing rats again. Some rats that were living indoors may have become trapped or there was another entry point to the home that was missed. A technician then returned to the property to re-inspect the home and see if a more thorough inspection could take place.
Upon returning to the property, the technician opened the access panel to the bedroom wall and found that the space behind it smelled terribly of rats. Fresh feces were found scattered in the wall void. Rats were clearly still living in this space, so the technician put the one-way door back. Snap traps were also placed behind the wall along with rodenticide. While rodenticide is usually used outside, it was used in this case to better reach the rodents living indoors. The technician spoke with the homeowner about the risk of foul odours in the walls, and they accepted. This was an ongoing problem that needed solving. If any terrible odours resulted from this treatment, the homeowner would agree to professional deodorizing. The Exterminators offer commercial-grade disinfecting and deodorizing services in which we remove all harmful pathogens and odours that pests leave behind.

Access Panel Rat Activity Toronto
Opening the access panel revealed what was happening within the wall void. Rats frequently burrow in walls, where they damage the insulation and contaminate it with feces.

A few weeks later, in late June, rat activity had decreased. The bait boxes outside showed signs of feeding but less so than the months prior. The rats were no longer being heard in the house, so the one-way door was removed once again. Over the next few weeks, the bait boxes were monitored closely for activity and rebaited as needed.
Rats are persistent pests, and in this case, they returned once again to plague this household. In October, the homeowners called The Exterminators again to report that they were hearing rats in the basement bedroom wall. The rats had clearly found another way into the house and attacking them with baits and traps was not enough.
A technician returned to the property, and this time, performed a thorough inspection of the deck and recommended opening the wall up to inspect the inside more closely. While no holes were found under the deck, there was evidence of burrowing there. There may have been a hole behind the drywall that connected to a crawlspace beneath the kitchen. The technician on duty suspected that rats were coming in from underground. The only way to find out would be to open the wall up, then seal it with mesh to stop the rats from getting in there.
A total of 21 feet of drywall was removed from the bedroom’s exterior wall, revealing some holes at the floor base. Rats commonly find weaknesses at the juncture where walls and floors meet, then nest in the insulation where it is warm. Here, they were indeed coming from the crawlspace beneath the kitchen. This could not have been found during the exterior inspection of the home as it was underneath the house. Using a HEPA vacuum, the technician safely removed the rat feces and debris within. The space was then disinfected with a fogger and galvanized steel mesh was installed against the wall to prevent any more rodents from entering. Another contractor that the homeowners hired would reinstall some fresh drywall.

Drywall Exclusion Rat-Proofing
Installing a galvanized steel mesh along the base of the wall would keep rats out for good.
Drywall Exclusion Galvanized Steel Mesh
Pest-proofing the wall like this also includes a thorough cleaning and disinfection of the wall, creating a fresh start that won’t be ruined by rats in the future.

Subsequent follow-ups showed that the interior exclusion worked. Rat activity within the home stopped and the rats outside were consuming bait. The technicians at The Exterminators continued to rebait the stations outside and monitor the situation closely to ensure that no more pests were getting inside. Over time, the rate of bait consumption decreased, so the rats were being eliminated.


Rats living behind walls are notoriously difficult to get rid of. Getting rid of them for good therefore takes thorough inspection and exclusion from the inside out. In this Casa Loma case, the rats did not stop until the wall was opened up and sealed from within. A full exclusion of the basement stopped the rats from getting inside while the bait stations outdoors kept them under control.
The Exterminators team vows to get to the bottom of every pest issue, no matter how difficult or complicated the case may be. If our initial treatment does not solve the problem, we will investigate further and follow a process of elimination to find the root cause. If contractual pests return during the warranty period, so will we. We send pests packing and keep them out with our guaranteed pest-proofing services. Call us today if you are experiencing a pest problem and we will arrive shortly for a detailed inspection and solution that works.