Bat Box Plans: How to Build a Bat House
Invite Bats into Your Garden with a Decorative Bat House
Bats are one of the best natural defenders against the arial attacks from mosquitoes and other flying pests. Each bat can devour over 1000 flying insects every evening. They are interesting to watch as they streak through the twilight skies, swooping and diving to grab their prey on the wing.
Though bats are one of the most beneficial predators in suburban areas, they are also one of the most miss-understood and under appreciated backyard inhabitants. They are also declining in many areas across the country, primarily due to the loss of habitat for adequate nesting and roosting sites.
You can help preserve a healthy and diverse wildlife ecosystem by inviting more bats into your backyard habitat with these bat box plans for an easy to make and decorative bat house.
Bat Box Plans: How to Build a Bat House
The Cutting List
Rough cut boards to the following dimensions:
- Part A - Roof: 11 1/4" L x 6" W
- Part B - Sides: 14" L x 2 1/4" W(Qty = 2)
- Part C - Back: 24" L x 11 1/4" W
- Part D - Front: 18" L x 11 1/4" W
- Part E - Divider: 12" L x 9 3/4" W
Bat houses can be made from nearly any of the wood products found at your local home center and lumbar yard. Cedar and pine boards are readily available, easy to work with, take paint very well, and are economically priced. Exterior plywood is another suitable option, especially since the finished bat box will be painted or stained. Exterior plywood is also available in sheets and half-sheets up to 4 feet wide, which makes it easier to construct larger bat houses rather than edge joining cedar or pine boards to form wider panels.
For this project, I selected a 1 x 12 pine board which was 8' long and I had plenty of material to complete the project, plus some leftovers for my scrap bin. The actual dimension of the 1 x 12 board is approximately 3/4" thick by 11 1/4" wide. Look for a board that is flat (not cupped) and has relatively few knots.
The bat logo was cut from a piece of thin plywood.
Cutting the Angles
The pieces for the back (part C) and the front (part D) of the bat box are cut at a 22 1/2 degree bevel across the top, to fit tightly up against the sloped roof. I used a table saw with the blade tilted to 22 1/2 degrees to make this cut, but a circular saw with the blade set to 22 1/2 degrees will work too.
The side pieces (part B) of the bat house each need a 22 1/2 degree cut at one end to accept the roof, and either a handsaw or a power miter box saw works well for this cut.The finished side pieces will measure 13 1/2" from the longest point to the bottom end of the piece. Cutting the length a bit long will allow the sides to be trimmed (if necessary) when fitting the bat box together for final assembly.
The roof (part A) of the bat box was cut slightly over-sized to allow secondary cut at a 22 1/2 degree angle to match the top of the back (part C) and the sides (parts B).Milling the back edge of the roof to a 22 1/2 degree angle improves the visual appeal and makes it easier to eliminate drafts and to waterproof the joints between the roof, back and sides of the bat house.
If you have a table saw, tilt the blade to 22 1/2 degrees, set the fence to the finished width of 5 3/4" and then run the piece through..
Scallop the Edges
To create the scalloped bat wing shapes on the back (part C) and on the front pieces (part D), use the drawing as a guide to create a pattern out of heavy paper or lightweight cardboard.
I find it easiest to create a "half pattern", which is essentially just one side of the pattern (one half of the wing). Center the half pattern to trace one side of the bat wing, and then flip the pattern over to trace the other side, creating a mirror image.
Cut out the bat wing shape, and then soften the cut edges with a rasp or sandpaper. If you have access to a router, a 3/8 cove bit produces a nicely finished edge.
Bats need a rough surface to land on and to cling to, and they will have difficulties grabbing on to the smooth surface of the board. There are several ways to roughen the inside surfaces of the front (part D) and back pieces (part C) of the bat house, as well as both sides of the divider (part E).
One of the easiest and most effective is to use a hand saw to repeatedly score the board's surface. Position the saw across the board, at a slight angle rather than straight across. A couple of back & forth strokes will score the surface. Reposition the saw a 1/2" from the first score line and repeat until you have covered the interior.
Since the top bevels are already cut to attach the roof of the bat box, check twice to ensure that you are scoring the insides of back and front pieces.
Now, re-position the handsaw at the opposite angle, so the resulting score line will cross the original score lines at an angle, creating a series of diamond shapes between the score lines (see photo). Continue the scoring until you have covered the interior of parts C, D and E, including the lower landing section of the back (part C) which extends down below the bat house. Lightly sand the score marks to remove any splintered edges.
Some Assembly Required
Assembling the bat box is straight forward and it can be simply glued and nailed or secured with screws; just make sure that the screws, nails and glue are all rated for exterior use. I used an exterior grade of yellow glue together with galvanized 1 1/2" finish nails to secure all of the pieces.
Before gluing or nailing, dry fit all of the pieces together to see if any adjustments are needed -- especially the width of the divider which needs to fit between the sides in the assembled bat house. It's much easier (and less frustrating) to test fit the pieces together now to make any final adjustments rather than trying to make changes after the bat house is halfway assembled.
One you are satisfied with the test fit, its time to begin the actual assembly of the bat house. I find it easiest to begin the assembly by attaching the sides (part B) to the front (part D). Position the sides on their back edge (the long side), and then lay down a bead of glue along the length of the front edge of the side pieces. Now position the front piece across the sides, ensuring that the scored section of the front piece is facing down towards the inside of the bat house. Also, line up the bevels at the top and then attach with nails or screws.
Don't Get Discouraged!
It can take a year or more before a colony of bats find your new bat house.
Flip the front and side assembly over on the workbench, spread a bead of glue along the long edges of the sides. Position the back (part C) and line up the bevels before nailing it into place. Then position and attach to the roof (part A) using glue and nails.
The last piece to nail into place is the divider, which separates the inside of the bat house into two sections. Since the opening is 2 1/4" wide, and the divider is 3/4" thick, positioning the divider in the middle of the opening will create two 3/4" wide chambers. With the bat box on its back, place two temporary spacers on the inside of the bat house, position the divider and then nail it into place. Now, just remove the temporary spacers and the divider is centered in the bat house.
Bats like warm, dark places for roosting and rearing their young. To help absorb and retain as much heat as possible, painting or staining the bat house with a dark color is recommended.
Lightly sand all of the corners and edges, for both a finished look as well as to help the paint adhere better. If there are gaps at any of the joints, seal the openings with an exterior caulk. I painted the bat box with three coats of a dark gray, flat exterior spray paint.
Add an Image of a Bat
To make the bat silhouette for the front of the bat box, draw an image of a bat with out stretched wings from a Halloween or similar model, or search web sites for anything bat-like to suit your taste. My version was derived from a movie advertisement, and drawn onto a thin piece of cardboard. The dimension is approximately 3" high x 8" long. I traced the cardboard pattern onto a thin piece of scrap plywood, and then painted it glossy black before attaching to the front of the painted bat house with glue and small nails.
Hanging Your New Bat Box
Hang the bat house facing an open area, preferably with a southern exposure to maximize the amount of warmth from the sun. The bat house should be mounted at least 10' up from the ground, and higher if possible.
The bat house can be mounted to the exterior of a building, or attached to a pole or a tree. Bat houses can be mounted at any time of the year, though bats are usually searching for new homes in the late winter and early spring as they emerge from hibernation or begin their annual migrations (depending on your geographic location).
Don't be discouraged if your bat box does not immediately attract any new residents; it can take time for the bats to find your "for rent" sign and move into their new accommodations.
The Bat World Sanctuary
A non-profit organization actively seeking to save and protect bats
From the Bat World Sanctuary web site website: "In a world where so many look away, Bat World Sanctuary is on the front line to end the abuse and destruction of bats. We are recognized as the world's leader in bat care standards and cutting-edge rehabilitation treatments, and we created specific guidelines for excellence in bat education programs that are used worldwide.
Each year we rescue thousands of bats who might otherwise die. Lifetime sanctuary is given to non-releasable bats, including those that are orphaned, injured, confiscated from the illegal pet trade and retired from zoos and research facilities.
Bat World Sanctuary was founded in 1994 and is a 501c3 non-profit, all volunteer organization with 20 rescue centers nationwide. Donations allow us to continue our rescue efforts for bats. You can help us save bats by educating others about their plight, and by donating to Bat World Sanctuary."
Please visit the Bat World Sanctuary web site for more information.
Bat Conservation International - We Need Bats, and the Bats Need Us
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Questions & Answers
Where do bats like to hide during the day?
Bats are nocturnal and active at night. During the day, bats take shelter in cracks and crevices in trees, rocks, and buildings. They leave their daytime roosts as dusk approaches. If you're lucky, bats will find your bat house and take refuge during the day in its tight spaces.
© 2011 Anthony Altorenna