Having bats in your yard will help keep mosquitos and other bugs at bay. One bat box can host up to 50 brown bats who eat thousands of bugs each night!
You might be surprised to know that the minimum size for a functional bat house is still larger than most birdhouses. The finished overall size of this piece is 18” wide x 26” high x 2-3/4” deep, with the accessible inside space measures 16-1/2” wide x 22” high x 1-1/2” deep.
Natural cedar is ideal for a bat shelter. We used three 1x6 fence panels. Fence panels are typically less expensive than finished cedar boards that are typically used for interior woodwork. The three boards used here cost $7.50.
Use a pencil and a speed square to mark 26” from the end on one board then stack all three boards to be cut on the chop saw at the same time. Measure 22” on the remaining length and then use the chop saw to cut all three boards down to size. These boards will compose the front and back of the bat house.
Use a wood joiner to attach the two sets of three boards together. The biscuits and wood glue used here work together to create a very strong connection, though there are many joinery options to consider depending on your resources, including pocket screws.
The three short boards will align to create the front of the bat house (22” long) and longer boards will form the back panel of the bat house (26” long).
On the 22” boards, avoid placing joinery around 6” from the bottom of the boards. A ventilation channel will be routed at this mark and could damage the joint. Place joinery higher and lower on the boards.
There are a few different ways to create texture on the inside of the bat house. Rough texture is necessary, it makes it easy for bats to grab on and nest comfortably in their dwelling. One method is to staple plastic mesh on the inside of the panels. The alternative is to cut small 1/4” horizontal grooves in the wood, making a ladder on which the bats can climb and cling.
A palm router with a 1/4” straight bit is perfect for creating horizontal grooves. Use a piece of clamped wood as a straight edge and set the router depth to plunge 1/4” deep (the grooves will be 1/4” x 1/4”). Continue routing these lines from the top of each panel, towards the bottom.
Adjust the router depth to 3/4” and use the tool to create a ventilation strip 6” from the bottom on the front panel. You may find it easiest to mark the location of the ventilation strip and then re-route the opening once the house is assembled so the straight bit can plunge through easily.
Now that you’ve finished the front and back panels of the house, trim the remaining lengths of cedar to size. Use the circular saw to rip the boards in half lengthwise and the miter saw to cut them to size. Use these pieces as the side walls and the roof of the bat house. You will need two 22” pieces and one 18” length.
Use a drill bit to pre-drill in the cedar and galvanized screws to assemble the walls. Lap the corners of the wood and screw through into the front and back panels.
Dark colors like medium-brown, dark brown or black are recommended for bat houses, because they help generate and retain heat from sunlight. Use only latex paint or a natural stain. Bats prefer warmer temperatures, 85 to 100 degrees Fahrenheit. Choose and apply a stain or exterior paint for the bat house.
Location is a big factor to consider when it’s time to install the bat box. The ideal mount is 15’-20’ off the ground, mounted on a pole, stand-alone tree or on the side of a building. Position the box to get maximum sun exposure. If you’re installing on a building, be sure there is ground beneath for the droppings to collect (as opposed to allowing them to sit on the roof). Batconservation.org recommends placing a two-foot wide metal piece below the box, so raccoons and cats can’t jump over it, but you also have to make sure to place it at least a few feet away from the bat house to allow the bats to drop and fly out of the house.
Use appropriate mounting materials to attach the bat house. To mount it on a tree, a t-plate bracket is attached to the back panel and two additional holes were drilled for screws in the bottom of the house.
Use an extension ladder and exercise caution while you install the house. Use a level for accuracy, and a drill to attach the 3-1/2” galvanized screws into the tree.