London, Ontario Case Study

Case Study: Big brown bats removed from London, Ontario home.

Quick Facts

Location: London, Ontario
Bat Species: Big Brown Bat
Problem: Bats using attic and wall cavities were occasionally showing up inside living areas.
Colony Size: Small, just a handful bats
Time of Year: June
Solution: Full exclusion and sealing

The Homeowner’s Problem

The homeowner contacted us after several bats appeared inside the home during the two years since purchasing the property. Neighbours had also observed bat activity around the roofline and chimney on the driveway side of the house.

Additional concerns included:

• Potential rabies exposure from bats entering living spaces
• Concerns that a large and growing colony was present
• Potential health risks associated with guano accumulation

Inspection Findings

Our inspection identified one primary bat entry point.

And, like every home, thousands of potential entry points.

There were no signs of a major infestation. In fact, more evidence of mouse activity was noted than bat activity. This is not unusual, as mice are far more common than bats and frequently use the same openings to enter buildings.

The signs of bat activity were so minimal that, had bats not periodically appeared inside the home, the homeowner likely would never have known they were present.

Primary Entry Point

A gap at the peak between the fascia and the brick wall was being used by bats to enter the attic.

Secondary Openings

One of the biggest reasons wildlife control companies fail at bat removal is because they only seal the obvious hole while missing the many secondary access points found on all houses.

Many additional gaps and problems areas were discovered around:

• Soffits
• Chimneys
• Roof intersections
• Utility penetrations
• Flashing transitions
• Front entryway
• Basement window
• Additionally an old style gutter guard was noted to have been incorrectly installed over the eavestroughs and was blocking them completely.

The Bat Species

The inspection confirmed the presence of Big Brown Bats, one of Ontario’s most common building-dwelling bat species.

Only two bat species commonly live in Ontario homes, but Big Brown Bats are overwhelmingly more common in large urban areas such as London, Ontario.

To learn more about the two primary species living in Ontario, Houses click below

Big Brown Characteristics:

• Frequently overwinter in buildings
• Uses attics and wall cavities
• Well adapted to our modern towns and cities
• Many never live in natural roosts.
• Will use the same structures year after year if access remains available
• Genders spend most of their time apart.
• Males do not help raise pups.
• Highly transient, often moving back and forth among several houses.
• Mainly eat flying beetles, moths and grubs. And very few mosquitoes.

Observations

Observations

Signs of a large active colony were not observed. It is more likely that local Big Brown Bats were using the structure intermittently.

No droppings were found in the attic or around the exterior of the home.

After speaking with the homeowner and examining the structure, I believe local bats were occasionally entering the attic and then either descending through wall cavities beside pipes and ductwork into the unfinished basement or, more likely, emerging from the wall beside a decommissioned zero-clearance fireplace on the main floor.

The decommissioned fireplace appears to be the most likely source of the interior bat sightings.

Although this is a century home, a modern zero-clearance wood-burning fireplace had been installed much later. These fireplaces vent through factory-built stainless steel chimneys. It was clear that the chimney had been removed and the roof opening closed in, as no chimney components or flashing were visible on the roof.

The removal of the chimney would have left a large open cavity, commonly known as a chimney chase. Building codes require combustible framing to remain at least two inches away from factory-built chimneys, creating a substantial open space around the chimney system.

This chase would have extended from the attic, where the bats were entering, all the way down to the fireplace on the main floor, providing a convenient route for bats to move throughout the structure.

Our Solution

Step 1: Complete Structure Inspection

The entire exterior was inspected to locate every potential entry point.

Step 2: Installation of one of our custom bat-exclusion devices.

A standard short exclusion device was installed over the primary entry/exit point

This allowed any bats to leave naturally but prevent them from re-entering.

Step 3: Permanent Bat-Proofing

At the same time as installing the bat excluder we…

Sealed every potential entry point.

Sealed all the large gaps between the bricks and soffits with foam backers and a wide bead caulk.

Modified the roof vents to make them bat, squirrel and raccoon proof.

Refastened all the loose aluminum fascia pieces tightly in place with aluminum zip screws

Removed the improperly installed gutter guards that were completely blocking the eavestroughs.

Performed a moderate amount of mouse-proofing work down low, sealing gaps above a basement window and placing screens in several weep holes.

Sealed numerous gaps in and around two chimneys and difficult to reach gaps in soffits

Modified a chimney liner cap venting the water heater, to make it bat-proof.

Step 4: Follow-Up Verification

A follow-up conversation confirmed that no additional bats have been observed inside the home. The customer was also provided with a lifetime warranty, giving them confidence that the problem has been permanently resolved. Provided that no one modifies or damages our work, the bats will never be able to re-enter the building.

Because we believe in doing the job right the first time, we also assured the homeowner that they would never have to pay us any additional money if, in the highly unlikely event, bats were ever to return and further bat-proofing work became necessary. Any required follow-up work would be completed at no additional cost under our lifetime warranty.

Conclusions:

Although the bats likely gained access to the living space by travelling down the empty chimney chase above the decommissioned fireplace, this pathway no longer posed a concern once the exterior entry points were bat-proofed and the bats were successfully excluded from the structure.

This project highlights several important facts:

• Bat removal is never about sealing a single hole.
• Every home has multiple potential entry points that must be identified and addressed.
• Permanent exclusion and sealing are the only reliable ways to prevent re-entry.
• Finding occasional bats inside a home does not necessarily mean a large colony is present.

Benjamin Vaughan/Residential bat specialist

June 10 2026

Need Help With Bats In Your Home?
If you’re hearing scratching noises in your attic, seeing bats flying from your roofline at dusk, or finding bat droppings around your home, professional exclusion may be required.
Contact Bat Control Specialists for help anywhere in Ontario.