Closing Up the Cottage: Fall Bat-Proofing Before Winter

Fall is the ideal time to bat-proof a cottage. The humane exclusion window — mid-August through October — lines up exactly with when you close up for winter. Maternity season, May to early August, blocks any sealing until the pups can fly, so for a cottage you close each fall, that trip is the natural time to seal it for good.

If you own a cottage on Georgian Bay, Lake Huron, or Lake Simcoe, the weekend you winterize is your best chance to shut bats out for good. This guide covers why absentee cottages draw colonies, what to check before you lock up, and why fall is the window that fits closing up.

When is the best time to bat-proof a cottage?

The short answer: fall, roughly mid-August through October — and it is no coincidence that it lines up with closing up. From May through early August it is maternity season, when sealing would trap flightless pups inside, which is illegal and inhumane. Once the pups can fly by mid-August, the colony can be excluded and every gap sealed as you winterize.

Spring, before pups are born, is also a valid exclusion window. But fall is the one most cottagers can actually use, because it is when they are on-site draining pipes and packing up. The timing is set by the bats, not by convenience.

Bats spend the warm months raising young in Ontario roosts. From May through early August it is maternity season. The roost holds pregnant females in spring, then flightless pups through the summer, and sealing a cottage would trap them inside. That is both illegal under provincial law and something no humane operator will do. Once the pups can fly by mid-August, the colony can be excluded properly, and the practical exclusion season runs through October before winter weather shuts the work down.

That mid-August-to-October window is exactly when cottagers drain the pipes, pull the dock, and pack up. So the fall window lands right when you are already at the cottage thinking about winter. The trick is booking early — the reasons behind the calendar are laid out in our maternity season guide.

Season	What the bats are doing	Can you bat-proof?
Spring (April, before pups)	Bats waking from hibernation; no pups yet	Sometimes — a short, weather-dependent window before maternity season
May – early August	Maternity season — pregnant females, then flightless pups	No — sealing traps them inside; illegal and inhumane
Mid-August – October	Pups can fly; colony still active before winter	Yes — the fall exclusion window, and it lines up with closing up
November – March	Bats hibernating inside the walls and attic	No — sealing traps hibernating bats that cannot wake and fly out

Big brown bats, the species most often found colonizing Ontario buildings, commonly hibernate inside the same walls and attic they used all summer. That is one more reason to finish exclusion in the fall — before they settle in for winter — rather than trying to seal once they are already hibernating inside.

Why do empty cottages get bat colonies?

A colony forms best where nothing disturbs it — and an absentee cottage is one of the quietest buildings on the lake. Almost every feature of a seasonal property works in a bat colony’s favour.

Empty and undisturbed all summer. When a cottage sits closed from October to May, a colony that moves in during spring maternity season grows for weeks with no interruption. The everyday disruption that breaks up colony formation in a lived-in house — doors opening, lights switching on, footsteps overhead — is simply absent. By the time you arrive, the colony is established.

Older construction. Many cottages across Grey Bruce Simcoe are forty to eighty years old, with original soffit boards, failed vent screens, and roof flashings loosened by decades of freeze-thaw. Cottages built in stages — a 1960s core with a later addition — hide entry points at every roofline transition.

Cedar-shake roofs. Common on older cottages along the Georgian Bay shore. Every lifted shake corner is a potential doorway once the underlayment has failed.

Close to roost habitat. Cottages sit next to forest, wetland, and shoreline, far closer to natural bat populations than a town home. That keeps the local colony dense and looking for space.

Most owners never lay eyes on the colony itself. They notice the evidence — which is what the next section is about.

What should you look for when you close up the cottage?

Before you lock the door for winter, do a deliberate check for bats. Colonies leave a consistent trail, and catching it now means the cottage can be sealed during the same fall window instead of waiting a whole year.

• Guano on the deck or under the soffit. Small dark grains that crumble between two fingers, usually piled beneath an active entry point. If there is a large accumulation, leave it — cleanup is a careful job, covered in our bat guano cleanup guide.
• A sharp ammonia smell. Urine soaked into attic insulation produces an eye-watering odour you often catch when opening upstairs windows.
• Dark oily staining on siding. Bat fur leaves greasy marks at entry points where the colony slips in and out night after night.
• Scratching or rustling in the attic or walls, especially at dusk as bats leave to feed.
• A bat indoors. Often the first sign an owner finds. If anyone slept in a room with a bat, treat it as a possible exposure and call your local public health unit — see do bats carry rabies in Ontario? for the details.

A dusk walk-around with binoculars is the most useful thing you can do yourself. Stand back at sunset and watch the rooflines for a quarter-hour to see whether anything flies out, and from where. The full room-by-room version is in our complete bat-proofing guide.

Why can’t you just bat-proof in the summer?

This is the question we hear most, and the answer matters. It is tempting to seal the gaps the weekend you find them in July — but doing so in summer is the one thing that turns a bat problem into a disaster.

From May through early August, bat pups cannot yet fly. Seal the entry points then and you trap the pups inside the wall or attic with no way out. That is inhumane, it is illegal under Ontario law for protected species, and it leaves you with a far worse mess than you started with. Even later in the year, sealing an active entry point without a one-way device shuts bats in rather than out.

That is why proper work is never just “caulk the holes.” A humane bat exclusion installs one-way devices that let the resident colony leave on its own and not return. Only once the last bat is out does every gap get sealed for good. That sequence is why the calendar matters — and why fall, once the pups can fly, is the window that fits closing up.

The fall closing-up bat-proofing walkthrough

Here is the order to work through as you close up. None of it is urgent in the panic sense — same-week is the pace — but the fall window is short, so the booking step matters.

1. Walk the exterior at dusk before you pack up. Binoculars, sunset, a quarter-hour of watching the rooflines. Note where any bats fly out.
2. Check the usual entry points in daylight. Soffit-fascia seams, gable and roof vents, chimney flashing, lifted cedar-shake corners, and rooflines where additions meet the original cottage. Oily staining marks an active door.
3. Read the signs inside. Guano, ammonia smell, scratching. Do not sweep or vacuum droppings — dried guano can release fungal spores when stirred up.
4. Leave the sealing to a humane exclusion. Do not close any gap yourself while bats may be inside. One-way devices let the colony out first; then everything is sealed.
5. Book the inspection now to hold a fall spot. The mid-August-to-October window fills fast across cottage country. An early booking gets the cleanest scheduling and a sealed cottage before winter.

Cottage country: Georgian Bay, Lake Huron, and Lake Simcoe

Cottage bat-proofing across our region sorts into a few shoreline patterns, and the fall timing works for all of them.

Along the Lake Huron shore, Sauble Beach is the most cottage-heavy town we serve — long exposure to lake weather wears on soffits and fascia, and cedar-shake roofing is everywhere. Our Lake Huron coast cottage guide walks that shoreline town by town. Up the Bruce Peninsula, Wiarton and the peninsula cottages back onto dense forest and shoreline where bats roost. Across Georgian Bay, Midland and the harbour towns carry deep heritage housing stock, with older soffits and rooflines that hide entry points. The full shoreline breakdown, county by county, is in our cottage bat removal guide for Lake Huron, Georgian Bay, and Lake Simcoe.

Wherever your cottage sits across Grey Bruce Simcoe and Huron, the exclusion process is built to run with or without you present. The inspection can happen whether the cottage is open or closed. One-way devices go up after maternity season, and the days it takes the colony to clear out do not need the cottage occupied. Most weekend owners hand us a key or share a code, and we keep them posted through each stage.

What does cottage bat-proofing cost, and what is the warranty?

Every cottage is different, so the honest answer comes after a look at the building. A single confirmed entry point is a smaller job than a full exclusion with several entry points, roofline work, or guano cleanup. After a free inspection you get a clear quote up front, with no pressure to book. You can see how a standalone job runs on our bat-proofing service page.

Every job we do is backed by our Lifetime Warranty:

If a bat re-enters through any point we sealed, we come back and do all the work necessary — at no extra cost. Forever.

The warranty is transferable to new owners with no expiration date. On a cottage — bought, sold, and passed between family for decades — that is a genuine asset to hand along, and it takes the bat question off a pre-sale inspection before it can ever cost you a deal.

Book before the window closes

If you are heading up to close the cottage this fall, that trip is your best shot all year to shut bats out for good. Walk the exterior, note what you find, and book a free, no-obligation inspection before you lock up. We cover the full Georgian Bay, Lake Huron, and Lake Simcoe shoreline across Grey Bruce Simcoe and Huron, the fall exclusion calendar opens in mid-August, and the earliest bookings get the cleanest windows. Seal it once, seal it right, and hand the next owner a bat-free cottage with a lifetime warranty attached.