Case Study Rats Infest Basement Walls in Dundas West

Case Study: Rats Infest Basement Walls in Dundas West

The following case study details a rat extermination in Toronto. A home in the Dundas West area suffered an interior and exterior infestation and had them removed with a comprehensive removal program and pest-proofing of the house.

Dundas West, Toronto

Dundas West, a heavily gentrified neighborhood in west Toronto, has come a long way in the past several years. Its proximity to downtown has attracted many young families into the area as well as exquisite restaurants, renowned galleries, and an assortment of small businesses that thrive in this buzzing nook of the city.

Dundas West 1953
Dundas West (looking east from Dufferin 1953).

With its dense population and century-old homes, Dundas West is prone to rat problems. Pests crawl from one property to another and take advantage of their aging structures to nest indoors.


The customer in this case called us to investigate the possibility of rats being present in the home. Rats had also been seen on the exterior of the property.

We dispatched one of our certified exterminators to conduct a thorough walk-through of both interior and exterior areas of the house. This is done for a couple of reasons. We first look for rat activity- any food scraps, droppings, damaged structures, etc.- to understand where rats are predominantly present. We then search for any entry points, both outside and inside, that can be used for rats to enter the home. This will help our professional exterminators determine the extent of the problem and plan the treatment.

Rat Entry Point Exterior
A potential point of entry was identified on the exterior of the property.

At this specific location, our technician was able to confirm activity both outside and inside the home. Entry points were also identified on the exterior of the property along a wall’s foundation. It was determined that an exclusion around that area was required to prevent rats from entering the home.

Foundation Gap Rodent Entry Point
The base of the exterior wall would need to be excluded to prevent rats from entering the home.

Initial Steps

As an initial measure, we placed two bait stations in the yard of the home near the compromised wall. These bait stations are filled with an attractive rodenticide that kills rats once ingested. The reason for the placement of these stations is to control the exterior rat population. They are also tamper-proof and locked with a key that only our technicians have access to.

Rodent Bait Station
Bait stations were placed outside the home to control the exterior rat infestation.

Inside the home, we placed several snap-traps. These traps are usually baited with a food item such as bacon or peanut butter. They instantly kill rats when set off. Placing rodenticide inside of home is rarely done because rats can die inside walls, subfloors, or other hidden spaces in the home, causing a fowl smell.


We returned soon after our first visit to preform an exterior exclusion. Our technicians placed a fine galvanized steel mesh sealing the point of entry and metal flashing along the base of the wall to both sides. This extra precaution will keep rats from digging near by and access the hole on the wall.

Foundation Gap Exclusion Metal Flashing
Metal flashing was used to seal off the bottom of the exterior wall.

Our technician also installed a one-way-door, which will stay in place for a few weeks. This door is especially designed to allow rats to exit the premises and not be able to re-enter. It will then be removed and sealed.

Rat One Way Door 1 1
A one-way-door was installed to allow any remaining rats to exit the house.

During the same visit, we re-filled all bait stations on the exterior as they had still shown some reduced activity.


We returned to the site after rat activity was apparently still present inside the home. We decided to relocate the one-way-door to a secondary entry point. This will eliminate the possibility that the rats could still be trapped inside the home and were not able to exit through our first one-way-door installation. After a few days, we returned to remove the one-way-door and sealed the hole.

After a few months, rat activity was still being seen inside the home. We re-visited the customer to investigate further.

At this point it appeared that most activity was concentrated in the basement area. An inspection behind the drywall showed exposed dirt and concrete deterioration. We suspected the rats were penetrating the home through the piping system and making their way up the walls and into the subfloor.

Rat Droppings Behind Basement Wall
An inspection behind a basement wall revealed rat activity, including rat droppings.

As a result, we proceeded to conduct an indoor exclusion in which we removed a section of the drywall in the basement and installed a fine galvanized steel mesh to protect the area from intrusion. This durable and strong mesh a capable of withstanding gnawing from rats and will prevent them from moving upwards the walls.

Wall Exclusion Galvanized Steel Mesh
Galvanized steel mesh was installed inside the basement wall to prevent rats from moving through the structure.

Our exclusion work is guaranteed for 2 years. If rats breach our exclusion within that time frame we will return and rectify the breach.

When we returned a few months later, we found that activity was still taking place outside the house, but our customer informed us that there were no more rats inside the home.


Rats can be a tricky pest to get rid of. They are capable of infiltrating spaces through different entry points and are incredibly good at concealing their hideouts. Our approach to eliminating a rat infestation usually begins with the elimination of the obvious points of entry- any holes, crevices, vents, etc. that expose the interior of the home. By controlling the rats both inside and outside with bait stations and snap-traps, we hope to have them all gone in no time.

In this particular situation we had to dig deeper into the problem as they remind a presence inside the home. Once exterior points of entry are sealed, we then look for access points inside. Our licensed exterminators are trained and experienced in finding these areas and were quickly able to target a specific area in the basement.

The customer now has a rat free home and peace of mind during our warranty period of six months.