How to Build a Bat House for the Backyard

Bats are one of the best natural defenses against mosquitoes and other flying pests, with each bat devouring over 1000 flying insects every evening. Bats 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. Bats 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 this easy to make and decorative bat house.

Difficulty: Moderate

Instructions

Things You'll Need:

• 1x12 Pine or Cedar board
• Basic woodworking tools

1. 
    

   Bat houses can be made from nearly any of the wood products which are commonly available at home centers and lumbar yards. Cedar and pine 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 house 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. The bat logo was cut from a piece of thin plywood. Look for a board that is flat (not cupped) and has relatively few knots.

2. To start, rough cut the 8' foot pine board to the following dimensions:
   
   Part A - the Roof: 11 1/4" long x 6" wide
   Part B - the Sides: 14" long x 2 1/4" wide (quantity of two pieces needed)
   Part C - the Back: 24" long x 11 1/4" wide
   Part D - the Front: 18" long x 11 1/4" wide
   Part E - the Divider: 12" long x 9 3/4" wide

3. The pieces for the back (part C) and the front (part D) of the bat house each have a 22 1/2 degree bevel cut across the top, to fit tightly up against the sloped roof. This bevel is cut easiest on a table saw with the blade tilted to 22 1/2 degrees, but the cut can also be made using a circular saw with the blade set to 22 1/2 degrees.

4. 
    

   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 house together for final assembly.

5. The roof (part A) of the bat house 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. 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.

6. 
    
   Bat house pattern

   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 light weight 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.

7. 
    

   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). Since the top bevels are already cut to attach the roof, check twice to ensure that you are scoring the insides of back and front pieces. 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.

8. 
    

   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.

9. Assembling the bat house 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 exterior grade glue 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 half way assembled.

10. 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.

11. Now flip the front and side assembly over on the work bench, 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 roof (part A) using glue and nails.

12. 
     
    Bat House Chambers

    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 house 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.

13. 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 house with three coats of a dark gray, flat exterior spray paint.

14. 
     

    To make the bat logo, 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.

15. 
     

    Hang your new 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 residences in the late winter and early spring as they emerge from hibernation or begin their migrations (depending on your geographic location). Don't be discouraged if your bat house does not immediately entice new residents; it can take time for the bats to find your "for rent" sign and move into their new accommodations.

Resources

• How to Create a Wildlife Habitat in Your Backyard

[survivoryea]

on 9/27/2009 Very detailed and good article - thanks for the information! 5*