How to Build a Bat House

The goal of a bat house is to create a shelter that mimics the space between bark and tree trunk. That means that a bat house should:

Provide an inside space that is very narrow. Bats like tight spaces.
Allow for the bats to stay warm inside through the use of caulking the sides for insulation and through painting the house a dark color.
Provide a rough inside texture of the bat house which allows the bats to more easily climb and get a foothold.

You can find a bat house construction plan from Bat Conservation International's website. (They also have a Bat House Builder’s Handbook available for free in a digital version on their bat house pages.) Note that the size of this bat house is quite large: two feet wide and almost three feet tall! A successful bat house can be smaller (14 inches wide instead of 24 inches wide), but this plan is designed to easily use up a 2 foot by 4 foot piece of plywood with fewer cuts.

Have you ever seen bat houses for sale that are smaller or shaped like a bird house? That just means those houses were made by people less acquainted with bat needs.

As you’re familiarizing yourself with the plan, ensure that you have a location with:

Lots of sun
A mounting space at least 15 feet off the ground (to protect against predators)
Ideally a water source nearby (so the mother bat doesn't have to leave her young for too long).

Interestingly, bats are less attracted to bat houses mounted on trees. There's a few reasons for this:

It's too easy for predators to get bats as they exit
The branches causing obstructions to exiting bats which drop down then up into flight
It's too shady from branches above

Bat houses mounted on buildings retain heat better and are less accessible to predators. You can alternatively put them on a pole.

If you’re following the Bat Conservation International plans, the supplies needed are:

1/4 sheet ( 2' x 4' ) 1/2" AC, BC, or T1-11 (outdoor grade) plywood. DO NOT use pressure treated wood.
One piece 1" x 2" (3/4" x 1 1/2" finished) x 8' pine
20 to 30 1 1/4" coated deck or exterior-grade Phillips screws
One pint dark, water-based stain, exterior-grade
One pint water-based primer, exterior-grade
One quart flat water-based paint or stain, exterior-grade
One tube paintable latex caulk
1" x 3" x 28" board for roof (optional, but highly recommended)
Black asphalt shingles or galvanized metal (optional)
6-10 7/8" roofing nails (optional)

A collection of woodworking tools and materials is presented on a plywood table.

Tools Needed to Build a Bat House

Table saw or handsaw
Caulking gun
Variable speed reversing drill
Paintbrushes
Phillips bit for drill
Tape measure or yardstick
Scissors (optional)
Staple gun (optional)

For those of you who do not normally buy wood, here are some tips:

Try to purchase Forest Stewardship Council certified wood and/or recycle scrap wood.
When you buy a piece of wood that is advertised as 1 inch by 2 inches, it is not actually that big when you measure it. It's more like 3/4 inch by 1 1/2 inches. That was important for me to know because it allowed me to use scrap wood for part of the project.

In addition to the supplies on the plan, we also recommend the following:

Two clamps for clamping wood while you saw or drill
Safety glasses for when you use power tools
A small broom for sweeping sawdust

Time commitment: 30 minutes

Measure and mark where you need to cut the wood according to the plan. Clamp it down to a sturdy spot for safety. You cannot safely hold the wood and the circular saw. Adjust the blade to the correct depth depending on the width of your wood. It takes only five cuts. Don't forget your safety glasses.

At this point, you can even take the wood and lay it together to get a sense of how it will look. You'll see that the bottom piece is the biggest. The 1x2 inch pieces form the sides of the bat house and then there are two smaller pieces of plywood on top. The gap between those two is a ventilation slot.

A large slab of unpainted plywood is shown, as a comparison, next to a stack of cut and measured plywood to be used for a bat house.

Time commitment: 2 hours

A collage of four images showcasing the measuring and cutting of plywood using woodworking tools such as an electric and hand saws.

This may be the most difficult part of making the bat house, but it's the most important. The goal is take the plywood, which is very smooth, and roughen it up to provide places for the bat to crawl up into the house. You can do this by cutting grooves into the wood. If you are going to use plastic mesh to help the bats climb inside your bat house, now is the time when you will staple it on. Make sure it hangs all the way down to the "landing pad" area, so bats have something to grab onto.

A note on this step:

When it came time to cut the grooves, what I found challenging was that I didn't know what type of tool to use.

At first, I was shy about using the circular saw, so I tried to use a hand saw. After 30 minutes and only three grooves, I realized I would have to rely on technology.

I set the circular saw to only 1/16 of an inch, re-clamped the plywood and started cutting grooves into the backboard. They were not always perfectly straight lines, but that's not important because trees do not have perfectly straight grooves either.

Once I had cut grooves over the whole backboard with the circular saw, I took my hand saw and deepened some of the grooves. I did this because I was not sure if the circular saw went deeply enough and also to roughen it up even further.

Time commitment: 1 hour

With a soft brush, sawdust is swept off slabs of plywood. Each piece is then hand painted with a dark walnut brown stain.

Bats like it dark inside their houses so it's important to stain all inside parts a dark color. First you have to sweep all the sawdust carefully from the backboard, especially from the grooves that you cut.

It's important to use stain rather than paint because paint would fill in the grooves you just cut. Stain just soaks into the wood nicely.

It only takes two coats of the stain, and the stain dries fast if you are making your bat house outside in the sun.

Time commitment: 30 minutes

Before adding the side pieces, apply caulk. This seals the bat house to help keep the heat inside. Baby bats need a warm home - reaching 80 to 100 degrees Fahrenheit in July.

Next you use your power drill to attach the side pieces. Since these pieces are rather narrow, they can easily split. A way to avoid splitting is to pre-drill the holes with a drill bit that is smaller than the size of your screw. Then, when you drill in the screws, they go in much easier and your wood stays whole.

Pieces of painted plywood are screwed together using an electric drill. Caulking is applied to provide heat insulation for bats.

Time commitment: 30 minutes

Next, attach the top two pieces of plywood. First caulk to ensure a snug fit. Then follow the same advice for drilling and attach the larger of the two top pieces.

Before you attach the smaller of the two pieces, measure to make sure your ventilation slot is about half an inch.

Two side-by-side detail images of the bat house building process. The plywood is screwed, caulked, and getting ready for final assembly.

Time commitment: 15 minutes

To ensure there are no gaps between all these pieces of wood where heat could escape, leaving our poor bats shivering in the cold, put some caulk all around the sides in any gaps that you see.

Finally, add a piece of wood to the top to form a roof.

A detailed view of an electric drill securing a final piece of plywood to form the roof of the bat house.

Time Commitment: Variable given paint drying time

Finally, we need to ensure the bat house lasts a long time, so we prime and paint it. We prime it with an exterior primer that discourages the growth of any plants or mold. Once the primer dries, paint the dark paint.

Time commitment: 20 minutes

Bat houses should be mounted on poles or buildings, which provide the best protection from predators. Wood or stone buildings with good solar exposure are excellent choices, and locations under the eaves often have been successful. All bat houses should be mounted at least 12 feet above ground, but 15 to 20 feet is better.

We hope you enjoy building your bat house, whether it's in celebration of bats at Halloween or any time of the year. Remember, once you put up the bat house, it may take a few years for a bat to find it. They will come looking in the springtime, so ideally it should be hung by late winter.