London Bat Case Study: Big Brown Bats and a Backyard Night Roost

This Old South London bat problem had two separate parts.

Summer exterior of a brick bungalow in Belleville Ontario that may require professional bat-proofing — **Bats were living in and showing up inside this London, Ontario house.**

Bat droppings on concrete beneath an exterior inside corner used by night-roosting big brown bats — **The homeowners were also finding a disproportionate amount of bat droppings each day by the back door.**

A small number of big brown bats were living inside the house and occasionally showing up in the living space.

At the same time, bats were night-roosting beneath a protected backyard overhang and leaving piles of droppings beside a door the homeowners used every day.

So we bat-proofed the house and humanely excluded the bats living inside it.

Bat control technician applying exterior caulking between the soffit and brickwork on a London Ontario home — A Bat Control Specialists technician seals a soffit-to-brick gap as part of complete exterior bat-proofing.

Custom bat excluder secured with screws at an inside soffit-to-brick corner on a London Ontario home — A custom bat excluder was installed over the active opening in this protected soffit-and-brick inside corner.

That solved the indoor bat problem.

But the droppings beside the back door continued.

That was when the project became especially interesting.

The bats living inside the house were gone, but bats from throughout the neighbourhood were still returning to the same brick-and-soffit corner to rest between feeding flights.

We eventually stopped that activity with a simple custom flashing system that removed the exact surface the bats needed to land and hang there.

It worked immediately.

A Big Brown Bat Colony Was Living in the House

The homeowners initially called us because bats were occasionally appearing inside.

There did not appear to be a large colony. We found very little guano in the attic and no evidence of a large maternity roost.

This was a small, typical big brown bat problem.

Big brown bats often live in houses in relatively low numbers. They move between different sections of a building and between different buildings throughout the year. They are highly transient and do not always leave behind large piles of droppings in the attic.

That can make the problem look smaller than it is.

A homeowner may see one bat inside, then nothing for several weeks, followed by another indoor appearance.

That does not mean random bats are flying through open doors and windows.

It means bats are living in the structure and occasionally finding their way into the occupied parts of the house.

We Bat-Proofed The House & Excluded The Bats

This house was not especially difficult to bat-proof. We identified the exterior openings, sealed the secondary gaps and installed humane one-way excluders over the active entry points.

The bats left the structure and did not get back inside.

Alt text: Small opening where the soffit meets the brick wall, allowing bats to enter the house. — A complete exterior inspection identified the active and potential bat entry points.

Beige exterior caulking applied along a soffit-to-brick gap to prevent birds from entering — Secondary roofline openings were sealed before the one-way excluders were installed.

The Bigger Clue Was Beside the Back Door

The most obvious bat evidence was not in the attic.

It was outside, beside the back door.

The homeowners were finding repeated bat droppings below the inside corner of a covered backyard overhang. The wall was brick, the ceiling above was aluminum soffit and the corner provided exactly the protected position big brown bats prefer for night-roosting.

This was not the bats’ main entry point.

It was a night roost.

That distinction matters.

Close-up of big brown bat droppings beneath a protected inside corner used for night roosting — The brick wall and soffit created an ideal high, protected resting place.

Bats do not establish their main entrance beside a frequently used door. There is too much movement, noise and human activity. In more than 30 years of residential bat work, I have never found a main colony entrance directly beside a regularly used doorway.

Their actual entry points are somewhere higher up on the house, quieter and more concealed.

Nighttime house diagram showing bats night roosting under a porch and entering through a soffit-to-brick gap at the side peak — Bats may night roost in a sheltered porch corner while entering the house through a completely different opening higher on the structure.

Diagram of a single-story brick house with a dormer and chimney, showing common bat entry points around soffits, rooflines, fascia, dormer edges, and where the soffit meets the chimney. — This diagram shows the most common places bats enter a house, including gaps at the gable end, dormer rooflines, fascia and shingle edges, and where the soffit meets the chimney.

They use roof edges, soffit intersections, chimneys, dormers, flashing gaps and hidden openings around the sides or upper sections of the house.

The porch was not where they were entering.

It was where they were resting.

What Is Bat Night-Roosting? Or What Do Bats & Smart Cowboys Have in Common?

Night-roosting is temporary resting behaviour.

Big brown bats leave their daytime roosts after sunset to feed and drink. They make several feeding flights during the night rather than remaining in the air continuously until morning.

Bat night roosting on a brick wall below a front door overhang, showing a common sign of bats using the porch or entryway area. — This bat is night roosting near the front door under the entryway overhang. Bats often rest in sheltered porch corners, front door overhangs, and covered entryways when they are using a home or nearby roofline.

Big brown bat hanging on the exterior wall of an Ontario home. — A big brown bat hanging outside an Ontario home. Big brown bats are the most common bat species found in Barrie, Ontario.

Between those flights, they need somewhere safe to rest.

They can return all the way inside the house, but that takes more effort and may repeatedly expose the colony’s main entry point to potential predators that eat bats like hawks and owls.

Instead, they often stop beneath a nearby porch, overhang or covered entrance.

The best night-roosting locations have:

A rough brick or stone wall they can grip
A soffit or ceiling directly above them
A protected inside corner
Enough height to remain away from people and predators
Open space below so they can drop and fly immediately

That is exactly what this house provided.

Overhead view of an Old West saloon showing a cautious cowboy sitting in the corner close to the exit — Smart Cowboy Theory: The smart cowboy sits in the corner close to the exit. He has fewer sides to watch and cannot easily be ambushed.

Two little brown bats wearing small cowboy hats hang in the inside corner of a porch on yellow brick beneath white soffits. — “Smart Cowboy Bats” — two little brown bats hanging in a porch corner like smart cowboys choosing the safest spot.

Why Bats Choose Brick and Stone (& Rough Surface Wood)

Alt Text Big brown bat hanging on the exterior brick wall of a London, Ontario home. Big brown bats commonly live in attics, walls, and roof systems and are frequently encountered during residential bat removal projects. — A big brown bat resting on the exterior wall of a London, Ontario home. Big brown bats are one of the most common bat species found living in residential structures throughout Southwestern Ontario.

Bat night roosting under the inside corner of a front porch — A bat hanging under the inside corner of a front porch. This is textbook night-roosting behaviour, where bats living in the house rest on porches, overhangs, brick corners, and sheltered exterior areas instead of returning all the way back into the attic or wall cavity between feeding flights.

Big brown bats need a rough, irregular surface they can grip.

Brick and stone work exceptionally well.

The joints, textures and projections give their feet and thumbs something secure to hold. That is why night roosts are so commonly found beneath brick and stone porches and overhangs.

Smooth vinyl siding and aluminum siding do not provide the same gripping surface.

Wood may occasionally work if it is rough, weathered or irregular enough, but the classic residential night roost is a brick or stone wall beneath a protected soffit.

This house had brick walls.

That detail was central to the problem.

Why They Press Themselves Against the Soffit

Bats do not choose these corners randomly.

Two bats outside their former entry opening after exclusion, unable to get back into the house. — Two bats remain outside their former opening after a humane exclusion prevents them from getting back into the structure. Note how high up they are against the soffits.

They are insect predators, but they are also prey.

A realistic nighttime illustration of a bat chasing a moth in flight while an owl swoops in from behind with talons extended. — Bats are both predator and prey: a bat hunts a moth at night while an owl closes in from behind.

Owls, hawks, snakes, raccoons and other animals will eat bats. That makes bats naturally cautious about where they rest and how exposed they are.

The bats at this house climbed as high as possible and tucked the upper ends of their bodies against the soffit.

That position reduced the number of exposed sides.

The wall protected them from behind.

The soffit protected them from above.

The inside corner protected one side.

They only had to watch the open space in front of them.

They were also high enough to drop away from the wall and become airborne immediately if something approached.

For a night-roosting big brown bat, it was almost perfect.

Night Roosts Often Reveal a Hidden Bat Problem

If bats did not night-roost around porches and leave droppings behind, many residential bat colonies would remain unnoticed much longer.

Bat droppings found on the ground outside an Ontario home below a possible bat roosting area. — Bat poop outside

Bat droppings scattered along a white window ledge beneath a screened opening used by bats. — Bat droppings collecting on a window ledge can indicate that bats are entering, exiting or roosting somewhere directly above the area.

Homeowners frequently discover a bat problem because:

Droppings repeatedly appear near a door
A security camera records bats beneath an overhang
Bats are seen hanging on brickwork after dark
A bat occasionally remains there through the following day
A bat is later found inside the house

The visible porch activity is not going to be near their main entry point.

That was true here.

The droppings were beside the door.

The bats’ main exterior entry openings were elsewhere on the house.

Bat-Proofing Solved the Indoor Problem—but Not the Night Roosting

We completed the exterior bat-proofing and excluded the small number of bats living inside the building.

Small roof vent protected against bat entry on a London Ontario home — This small roof vent was secured as part of the home’s complete exterior bat-proofing.

ridge vent secured against bats during complete bat-proofing — A ridgevent was inspected and protected to eliminate another possible bat entry point.

Large roof vent covered with custom metal screening to prevent bat entry — Custom screening was installed over the larger roof vent to block bats while maintaining attic ventilation.

The indoor appearances stopped.

The colony was gone.

But the droppings beneath the backyard overhang continued. Why?

Because the night roost was not being used only by the bats that had lived in this particular house.

Other big brown bats from the surrounding neighbourhood were using it too.

The house sat directly beside Southcrest Ravine, part of the Coves subwatershed in Old South London.

This was prime big brown bat habitat.

The ravine offered:

Heavy insect activity
Mature trees
Sheltered flight corridors
Water nearby
Darkness
Open feeding areas
Houses immediately beside the feeding grounds

The bats were not living in the ravine.

They were feeding there.

They were living in houses throughout the surrounding neighbourhood.

The wooded ravine was their hunting ground, and this backyard overhang was a convenient rest stop right beside it.

Old South London Coves Ravine Big Brown Bat Habitat — The house sat directly beside Southcrest Ravine, giving neighbourhood big brown bats immediate access to feeding and watering habitat.

Backyard in Old South London overlooking a wooded ravine where big brown bats feed at night — This Old South London backyard overlooks a wooded ravine used by local big brown bats as nighttime feeding habitat.

Wooded ravine behind an Old South London backyard where big brown bats forage at night — Mature trees, insects, shelter and nearby water supported regular big brown bat activity.

These Bats Were Living in Neighbourhood Houses

Big brown bats in urban London are house bats.

They live in walls, soffits, chimneys, attics and other protected construction cavities.

Modern houses give them something natural roosts often cannot: multiple temperature zones.

A bat can move higher when it wants warmth, lower when it needs cooler conditions and into different sections of a structure as the weather changes.

Big brown bats also move between houses.

They are highly transient.

The bats using this night roost were likely living in several homes around the ravine. They fed over the trees and water, then returned to nearby houses or stopped beneath this overhang between feeding flights.

The small number living in the case-study house was only part of the activity.

The Custom Flashing Solution

Bat-proofing the house did not remove the night roost because the night roost was on the exterior.

The bats were not entering through that corner.

They were gripping the bricks and resting beneath the soffit.

We needed to remove the gripping surface without rebuilding the porch.

The solution was custom metal flashing.

We installed smooth flashing across approximately the upper six to seven inches of brickwork, extending about five feet in both directions from the inside corner.

That covered the exact area the bats needed.

They could no longer grip the upper brickwork.

They could no longer press themselves tightly against the soffit.

The metal was too smooth and the remaining exposed brick was too low and too far from the protected corner.

They did not simply move down the wall.

They stopped using the night roost.

It worked like a charm.

Before: exposed brick beneath the soffit

Protected brick and soffit inside corner before custom flashing was installed to stop bat night roosting — The rough upper brickwork gave the bats a secure gripping surface directly beneath the soffit.

Horizontal measurement of a brick wall before custom flashing was installed to prevent bat night roosting — The full length of the brick night-roosting area was measured so the custom flashing could be fabricated to fit properly.

Vertical measurement taken before installing custom flashing to stop big brown bat night roosting — Custom metal flashing was fitted across the upper masonry around the protected inside corner.

During: fabricating & installing the flashing

Technician fabricating custom metal flashings to stop bats from night roosting on a London Ontario home — Custom metal flashings were measured, cut and formed on site to cover the brick surfaces where big brown bats had been night roosting.

Partially installed custom metal flashing beneath a soffit to stop big brown bat night roosting — Custom metal flashing was installed beneath the soffit to cover the rough brick surface and prevent big brown bats from night roosting there.

Technician installing custom bat flashing beneath a soffit on a brick house to stop bat night roosting — Custom bat flashing being installed beneath the soffit to stop big brown bats from night roosting on the exterior of the home.

Technician installing custom metal bat flashing beneath a porch soffit on a London Ontario home — Custom metal flashing being installed beneath the overhang to stop big brown bats from night roosting on the brick wall.

Custom metal bat flashing being caulked beneath a soffit on a London Ontario home — The custom bat flashing was carefully caulked along the soffit to create a clean, continuous seal and prevent bats from getting behind it.

Custom metal bat flashing being caulked against a brick wall beneath a soffit — The custom bat flashing was carefully caulked along the brickwork to create a continuous seal and complete the night-roosting repair.

After: completed smooth flashing

Custom metal flashing installed along a brick porch overhang to stop big brown bats from night roosting — **The finished flashing removed the bats’ foothold and stopped the night-roosting activity.**

The Final Result

We solved both parts of the problem.

First, we bat-proofed the house and humanely excluded the bats living inside it.

The indoor appearances stopped.

Then we addressed the separate exterior night roost.

The custom flashing prevented neighbourhood bats from gripping the brickwork beneath the backyard overhang.

The droppings stopped.

The bats moved elsewhere.

They are almost certainly still living in other houses around the ravine and feeding over the Coves at night.

They simply cannot use this particular porch as their rest stop anymore.

What This London Bat Case Study Proves

This project demonstrates several important facts about big brown bat behaviour:

A night roost is not an entry point.
Bats commonly night-roost beneath brick and stone overhangs.
They strongly prefer high inside corners directly beneath soffits.
Heavy porch droppings can be produced by more bats than are living in the house.
Bat-proofing the structure may not stop exterior night-roosting.
Smooth custom flashing can eliminate a preferred night roost.
Homes beside ravines and wooded corridors can experience heavy neighbourhood bat activity.
Big brown bats in cities live in buildings, not in the woods where they feed.

Frequently Asked Questions About Bat Night-Roosting

Bat Control is A Complicated Speciality.

Bat control is more complicated than it looks, and not every wildlife company knows how to do it properly.

Watch the video and read the article below to learn the difference between national chains, local wildlife companies, and true bat specialists—and what to look for before hiring anyone.

What to Look for in a Bat-Control Specialist

Why are bats leaving droppings beside my door?

They may be night-roosting beneath the porch or overhang above it. Bats often rest between feeding flights and leave droppings below their temporary resting place.

Does that mean the bats are entering beside the door?

Usually not. The night roost and the main entry point are often in completely different parts of the house.

Why do bats night-roost on brick?

Brick and stone provide rough surfaces bats can grip securely. Smooth siding usually does not.

Why do bats choose inside corners?

Inside corners provide protection from above, behind and from one side. Bats can rest with fewer directions exposed to predators.

Will bat-proofing the house stop night-roosting?

Not necessarily. Bat-proofing prevents bats from entering the structure. Exterior night-roosting may continue if bats from other nearby colonies still use the porch.

How do you stop bats from night-roosting beneath an overhang?

The gripping surface must be altered or covered. In this case, smooth custom metal flashing installed over the upper brickwork stopped the bats from landing and remaining beneath the soffit.

Are the bats living in the nearby ravine?

They feed and drink in the ravine, but big brown bats in urban London primarily roost in houses and other buildings nearby.

Can a small colony create a lot of droppings outside?

Yes. A night roost may be used by bats from several nearby houses, so the exterior droppings may greatly exceed what would be expected from the colony inside one building.

Need Bat Removal in London, Ontario?

Bat Control Specialists provides humane big brown bat exclusion, complete exterior bat-proofing and custom solutions for difficult night-roosting problems.

Request a London Bat Control Assessment

Our completed bat-proofing work is protected by our lifetime warranty, so if bats regain access through an area we treated, we return and correct it at no additional charge.

Why Our Warranties Are Different

London Ontario Bat Case Study: Big Brown Bats Night Roosting on a Ravine Home