Bat Houses After Exclusion: Should You Install One, and How?

After we have excluded bats from your attic or walls, many homeowners ask the same question: should we put up a bat house? The short answer is yes, if you are willing to install it correctly. Here is why bat houses matter, where they belong (and where they do not), and how to give yours the best chance of attracting tenants.

Why install a bat house at all

Bat populations across Ontario have collapsed. The little brown bat — the species most often displaced from homes across Grey Bruce Simcoe — is listed as endangered under the provincial Endangered Species Act. White-nose syndrome, a fungal disease that hit North American hibernation sites in the late 2000s, has destroyed millions of bats across the continent. The provincial summary, with current status and recovery information, lives at the Government of Ontario’s Little Brown Myotis page.

Excluded bats need somewhere to go. The colony we just removed from your attic was, in almost every case, doing useful ecological work — a single little brown bat eats thousands of flying insects per night. After exclusion, those bats scatter to find new roosts. Some succeed; some do not. A bat house gives the local colony a legitimate alternative habitat so it can stay in the area and keep doing that work, just not inside your roof.

There is a practical benefit too. A successful bat house with even a small colony noticeably reduces mosquitoes, moths, and other flying insects in your yard through the summer. People who install bat houses in cottage country often notice the difference within a season or two of a colony establishing.

The honest disclaimer: bat houses fail to attract bats more often than they succeed. The good news is that most failures are about location, mounting height, sun exposure, or model — all things you can fix before you ever drive a screw. The next sections cover what gets a bat house used.

Will the same bats move from your attic into the bat house?

Sometimes, but usually not right away. The colony we excluded does not gather politely at the bat house you put up next door. Individual bats find individual roosts as they scatter — barns, tree cavities, other attics, other buildings — wherever each bat ends up.

What more commonly happens is that a future colony establishes in your bat house over a one-to-three-year window. If your siting is right, you may see scout bats checking the box the very first summer. A full maternity colony often takes longer.

Patience matters more than most homeowners expect. The bat house gets quieter the more often you check on it during the day. Most failed bat houses fail because the homeowner gave up after one season or assumed the box was a dud. The boxes that succeed are the ones that stayed up long enough to be discovered.

Where to install a bat house (and where not to)

Siting is where most bat houses succeed or fail. The rules are specific.

Mount on a building or pole, not a tree. Trees are the obvious mounting spot for someone new to bat houses, and they are almost always the wrong choice. Trees provide too much shade, give predators easy access, and move in the wind. A south- or southeast-facing wall of a barn, garage, or dedicated post is the right answer.

At least 12 to 15 feet off the ground. Higher is better. Bats need clear flight paths under the entrance — they drop from the box to take wing rather than launching from a perch.

Six to eight hours of direct sun per day. Bat houses need to reach internal temperatures of 80 to 100°F (27 to 38°C) on summer days for maternity colonies to use them. In Ontario’s climate, that means lots of southern exposure. A north-facing wall almost never gets warm enough.

Away from bright nighttime lights. Streetlights, driveway floods, and barn lights deter bats — and worse, they attract owls, which are bat predators. Pick a spot that stays dark after sunset.

Near water, but not over it. Within a quarter mile of a pond, lake, river, or wetland is ideal. Bats drink in flight by skimming water and hunt insects over wetlands. Cottages along Georgian Bay, Lake Huron, and Lake Simcoe are well-suited to bat houses for this reason.

At least 20 to 30 feet from your home’s sealed entry points. This one is specific to post-exclusion installation. Do not mount the bat house right next to where we just sealed your soffit or fascia. Bats may probe the sealed area looking for re-entry, and proximity makes the wrong spot too tempting. Distance gives the bat house a clear advantage.

What not to do. Do not mount on a tree. Do not install in deep shade. Do not mount below 10 feet. Do not install over a busy walkway, a deck, or a doorway — guano accumulates below the box and you do not want it on a high-traffic surface.

What kind of bat house to buy or build

Once siting is sorted, the box itself matters.

Multi-chamber designs outperform single-chamber. A box with three or four internal chambers gives bats temperature options through the day and holds significantly more individuals.

Larger surface area is better. At least 14 inches wide and 24 inches tall is a sensible minimum. Larger boxes hold larger colonies and stay warmer through cool nights.

Untreated cedar or rough-cut pine are the standard materials. Avoid pressure-treated lumber and avoid painted interiors — bats grip the inside surface, and chemicals or smooth paint defeat that.

Exterior color matters by climate. In Ontario, dark colors — chocolate brown, black, dark gray — help the box absorb daytime heat and hold it through cool nights. White or light-colored boxes are designed for hot southern climates and run too cold here.

Roughened interior and a landing pad under the entrance let bats climb in. Most reputable manufacturers build this in.

Bat Conservation International–certified designs are a reasonable shortcut to a working model if you are buying rather than building. DIY plans are widely available too — the same dimensional rules apply.

What to expect after installation

Realistic timelines prevent unrealistic disappointment.

First month: likely no activity at all. The local bats are still establishing post-exclusion patterns and have not yet noticed the new option.

First season: you may see scout bats — single bats checking the box at dusk, roosting briefly, then leaving. This is a good sign and means the box has been discovered.

Second season: more frequent visits, possibly a small group roosting at dusk or briefly during the day.

Years two to three: if the siting is right, a small maternity colony often establishes. This is when the bat house earns its keep.

What success looks like. A small accumulation of guano on the ground below the box (compost it into your garden — it is an excellent fertilizer), plus visible dusk-emergence activity on summer evenings.

What failure looks like. No activity after two to three full seasons. The box is in the wrong spot. The most common fixes are moving it to a sunnier wall, raising it higher, or relocating away from a nighttime light source.

How this fits with our exclusion work

We do not sell bat houses, and the box is not part of any service we charge for. We recommend them to homeowners who want to support the local bat population after we have sealed their home — a small, voluntary conservation step that fits with the work we just did.

Our warranty is unaffected by whether you install a bat house:

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 bat house is alternative habitat for new colonies, separate from the structural work on your home. If a bat ever re-enters through one of our sealed points, the warranty applies regardless of what is or is not mounted on a pole at the edge of your yard. We have done this work on hundreds of homes and thousands of entry points across Grey Bruce Simcoe, and we treat the warranty as a permanent commitment.

When to call

If you are still in the exclusion stage — bats are active in your attic or walls, or you suspect they might be — start there before thinking about a bat house. Free on-site quotes for bat removal and exclusion across Owen Sound, Barrie, Collingwood, and the rest of our service area. Once your home is sealed and the colony is settled into its new patterns, the bat house is a kind, low-cost step you can take to give those bats somewhere worth going. More about us at our homepage or about page.