Introduction: Bat House
Why would anybody want bats in their yard? There are lots of good reasons but my three favorite reasons are "the three P's" of Pollination, Poop, and Pests!
Bats are attracted to flower nectar just like bees and (like bees) pollinate as they visit from flower to flower. Since they "work the night shift," bats pollinate all night like bees do all day.
My second favorite reason is the guano bats produce. Bat guano (poop) is so incredibly rich in nutrients that wars have been fought over the harvesting rights to it. Bat droppings have an ideal ratio of NPK (nitrogen, phosphorus, and potassium, the elements required for plant growth, )have a high percentage of living organisms making it a natural fungicide that destroys nematode worms, all of which promotes a natural, global ecosystem.
My third, but most important, favorite is pest control - bats feast on as many as 1,200 insects each hour and mosquitoes are a major part of their diet. If you’ve ever grown your own garden, you know how difficult it can be to combat bugs, particularly if you are committed to avoiding harmful pesticides. Bats eat the bugs responsible for wreaking havoc on your garden.
Bat houses give females a safe, warm place to raise their young. Because bats typically only have one pup each year, populations are slow to grow. Plus, because of habitat loss, bats are finding it harder to find places to roost during the day and to raise their young.
By installing a bat house, you give these pups a chance to survive and for populations to be healthy. And all those healthy bats mean we can use less pesticide on our plants—a win win for everyone.
Without bats, humans would be in trouble. Bats help control insect populations, reseed deforested land, and pollinate plants, including many that we eat. Researchers and scientists also learn from bats to improve medicine and technology.
As population encroaches on forested areas, loss of habitat has endangered many species of bats. Building a bat house provides a safe place for bats to live and a nursery for their young.
There's a lot to know about proper placement of a bat house and thankfully the internet is filled with great sites offering detailed information regarding that. How high off the ground, how close to forest growth, how close to body of water, what color to paint the bat house (to maintain optimum internal temperatures,) compass orientation (for optimum sunlight exposure,) and method of mounting the house are a few of the interesting variables to consider.
So, let's get started to make a proper, weather-tight bat house with good ventilation and proper dimensions.
Step 1: Materials
You can use most any wood, but cedar is recommended for its weather resistance and insect repelling properties. I am typically against painting cedar, but a good skin of outdoor water-based latex paint (as good a grade of paint as you are comfortable with) will add years of life to your bat house. You will want to use liberal amounts of yellow carpenter's glue or silicone caulk - or use both to provide as dry an interior as possible.
One 3’ foot long 1" X 8" (7¼")
One 2’ X 2’ sheet of T-111 exterior siding or rough sided plywood.
One 8’ foot long 1" X 6" ( 5½")
One 4’ by 4’ sheet ¼” plastic mesh
One 6’ foot long 1" X 4" (3½")
46 - 1 5/8" #8 galvanized wood screws.
Two 3’ foot long 1" X 1" (¾")
Paint and painting tools
Electric drill, saw, measuring tools, heavy duty stapler
Step 2: Carefully Select Lumber and Cut Pieces
Following the excellent (and free) shop plans from http://www.floridabats.org, I dug through the lumber at Home Depot to find 1x boards of cedar. Take your time and dig through the supply of lumber to find boards that are straight and free of defects such as cracks and large knots.
I brought the wood home, and cut it into the various lengths called for in the plans. Most lumber sources will cut for you - especially helpful with sheet goods.
From the 1X6, cut six 14" sections for the front and back panels of the bat house.
From the 1X8, cut one 16" section for the roof and one 14" section for the back.
From the 1X1’s cut four 17" sections. These will be used as spacers to secure the partitions.
From the 1X4, cut one additional 14" section for the back.
From the remaining piece of the 1X4 cut two sections for the sides. One end of each piece will be cut at a 30-degree angle for the roof. This can be done by cutting each piece with a front length of 21½" and a back length of 23½".
From the T-111 or plywood sheet, cut a 17"X12" section for the back partition, and a 16"X12" section for the front partition. If a larger piece of plywood is available, these two pieces can be cut 12½” in width to provide a flush fit at either side.
I had some ¾” OSB left over from another project, so I saved about $15 on materials; I made the two baffles out of OSB instead of the marine-grade plywood the plans specified. I would normally be concerned about how OSB deteriorates when wet, but since the baffles are inside a rain-tight box, I gave them three heavy coats of paint before assembly and figure they will do just fine.
The plans were accurate, so cutting all of the pieces can be done without regrets. Having everything pre-cut helps dry fitting pieces; the dry-fitting process helps visualize how the project comes together.
Step 3: Glue and Screw
Before any assembly, plan your steps so you can anticipate when glue is needed or best time to apply caulk. As pieces come together, it can become difficult to spread glue or apply caulk into tight spaces.
You can score the interior pieces (cut a very shallow groove every 1/2" or so) to give the bats something to climb on/cling to - or you can staple a plastic mesh material to interior surfaces . . . most folks go with the mesh. Just make sure you don't cover up your grooving or the mesh with paint - it renders it unusable by the bats.
After fastening mesh material, everything goes together using construction screws (with star pattern drive.) You can use any type of screw, however, it should be a wood screw, it should be weather resistant, and it should be short enough to avoid poking through to leave exposed screw tips to harm the bats. A construction screw works well - it not only stands up to outdoor conditions, it has a six-pointed star drive which will not spin out during installation (important when using heavy lumber that this project calls for.) Don't have a star drive bit for your drill? No problem - a bit is packed with each and every box of these screws (but check to make the bit it is in the box.)
Pre-drill all holes to prevent splitting wood. Use a drill bit slightly smaller in diameter than your screw. Seat each screw firmly making sure you don't leave any exposed screw tips to harm bats. Spread glue just before screwing; clamping is not necessary if screwed properly, however using clamps sometimes helps hold pieces firmly while you pre-drill holes and install screws.
All joints receive a coating of waterproof carpentry glue. When the glue dries, all corners receive a generous bead of silicone caulk; you should plan to do one or the other, but I recommend doing both to ensure a dry interior and extended life.
Step 4: Construction Steps
1. Place the two side pieces on a table with the long sides up and 14" apart (outside to outside). It is recommended that glue or caulking be used as the bat house is assembled to strengthen and weatherproof it. Place one of the 14" X 6" pieces on top and align it with the bottom of the two side pieces. Fasten it with two 1-5/8" wood screws on each side. Drilling 3/32” pilot holes for all screws will help prevent the wood from splitting. Repeat the process with a 6", 4", 6" and 8" piece, in that order. This will place the 8" piece at the top of the bat house.
2. Now turn the bat house over so it is laying on its back. Drill one 5/16" hole at the top, and one 5/16" hole bottom. These will be used for mounting the bat house to a post or building - skip these holes if you plan to use a French cleat mounting system. If you do drill the holes, they should be located in the center and 2" from the edge.
3. If plastic mesh is being used, cut two sections of plastic mesh the same dimensions as the plywood partitions. Staple the mesh to the plywood using vertical rows of staples about 2-3” apart. The side with the mesh will face the front of the bat house. Cut a section of plastic mesh 12" wide and 23" long and place it on the back wall of the bat house. Fasten the mesh with vertical rows of staples about 2-3” apart.
4. Position the 1X1’s in the left and right-hand corners with the bottom ends located 4½" from the bottom of the bat house. This will create a 4½" landing pad. Place the 17" partition with the rough or mesh covered side up on top of the two 1X1’s already in position. Use three 1-5/8" wood screws in each; one in the center and the other two about ¾" from each end. Make sure the top wood screw securely attaches the 1X1 to the 8" board on the back wall. This will add strength to the bat house
5. Position the remaining two 1X1’s on each side of the partition directly above the previous two. Place the 16" partition on top (rough or mesh side up); allowing 1" of the previous 1X1’s to show at the bottom. This open space makes it easier for bats to crawl into the forward crevices. Now fasten the plywood section and 1X1’s using two 1-5/8" screws on each side. Locate them about 1½" from the top and bottom of the plywood partition to avoid the screws underneath.
6. Place the beveled 14" X 6" board at the top of the front, aligning the beveled edge with the 30 degree angle of the two side pieces. Fasten it using two 1-5/8" screws on each side. Repeat using a second 14" X 6" board. Locate the third and final 14" X 6" board about ½" down from the previous one to form a ½" gap for the vent. This vent is important as it creates different temperature zones inside the bat house - bats will gravitate to different temperatures depending on maternal status, age, etc. and the vent gives them that choice.
7. Center the roof section such that there is equal overhang on each side. Fasten it to the side pieces using two 1-5/8" screws on each side. The roof should be caulked where it meets the back wall. Adding roofing material and painting the bat house will greatly extend its life.
Paint color and texture also regulates bat house temperature. Paint color should be black where average high temperatures in July are less than 85° F, dark colors (such as dark brown or dark gray) where they are 85° to 95° F, medium colors where they are 95° to 100° F and white or light colors where they exceed 100° F. Much depends upon amount of sun exposure; adjust to darker colors for less sun. For the interior, use two coats dark, exterior grade, water-based stain. Apply stain after creating scratches or grooves or prior to stapling plastic mesh. Paint fills grooves, making them unusable. Use exterior-quality, water-based stain or latex paint, and choose flat paint rather than gloss or semi-gloss paint for best solar absorption.
8. The bat house can be mounted on a 4’X4" post or the side of a building using the holes drilled in #2 above and three-inch long, 5/16" lag bolts. Alternately, a "T" brace using a cleat for the cross member can be used and anchored to a second cross member using screws in both lower corners. A large galvanized or stainless steel washer (fender washer) is recommended to protect the wood. Mounting on trees is not recommended because they have proven to be the least successful location for bat houses. Bat houses should be located at least ten feet above ground. Experience indicates the higher the bat house is mounted the more likely it will get bats; optimum elevation is between 12 and 20 feet above ground level.
Step 5: Mounting the Bat House
The bat house received several coats of paint (even though cedar weathers quite well) and is ready to mount on a post. I used a 4x4 pressure treated wood post that is 11' above ground level. I attached a brace made of pressure treated 2x4 wood to bring the bat house up to a 12' elevation.
All bat houses should be mounted at least 10 feet above ground, and 12 to 20 feet is better. Choose a sunny location on the East or South facing wall of your house or pole-mounted out in the yard. Bat houses work best with at least 6-8 hours of direct sunlight (if only partial day sun is available- morning sun is preferable). Never mount a bat house to a tree or near vegetation - bats need plenty of unobstructed "air space" around their house for take offs and landings.
The bat house is mounted on a brace (a departure from the plans as regarding mounting instructions) because I wanted to provide extra strength against severe winds and I wanted to be able to take the box down for cleaning and repairs. As it turned out, my choice of mounting method also made it a lot easier to install.
I used what is known as a “French cleat” on the back of the bat house that mates with an opposing cleat atop the mounting brace. A French cleat will not only hold an enormous weight, it will prevent sagging or loosening over time. Two construction screws secure the bottom of the bat house to the lower cross member of the mounting brace, so it is firmly in place.
Before mounting, I gave the post and the brace a couple of coats of outdoor paint. The French cleat made it easy to slip the bat house into place; a construction screw was driven through the bottom corners of the house into the 2x4 brace to anchor it securely. It should stand up to the strongest winds and rain Florida can dish out.
Step 6: Open for Business
We're up and ready for bats. The research suggests it can take as long as a year for bats to adopt a new bat house. Bat houses can be installed at any time of the year, but they are more likely to be used during their
first summer if installed before the bats return in spring. When using bat houses in conjunction with excluding bats from a building, install the bat houses at least two to six weeks before the actual eviction, if possible.