Bat houses are a great way to cut down on local pest insects and encourage biological diversity. However, a badly made or mounted bat house may not attract very many bats. A functional bat house must be the right size, protected against drafts, and mounted correctly. Height, proximity to nearby objects and other elements could make a big difference in whether your project turns out to be bat heaven.
Locate the right spot for your bat house. Choose a pole, building or tree clear of other obstructions and situated away from bright lights. Bats inhabit pole-mounted bat houses faster than tree-mounted houses, because trees offer predators more climbing opportunities. Trees can also get in the bat's way, but may be the only mounting choice.
Choose a mounting point. It should be at least 10 feet above the ground and located so that that bats receive at least some sunlight. Bat houses in temperate climates should get at least six hours of sun per day. The colder the climate, the more sun your bats will need. Higher bat houses are more likely to be occupied.
Measure your mounting point to find out how far apart screws should be. Attach your bat house to solid material, such as wood, rather than siding or a weak spot.
Choose mounting rails. Heavier bat houses will require 1 inch by 4 inch lumber, while light bat houses may need only 1 inch by 2 inch boards. Cut your mounting rails to 6 inches longer than your bat house is wide, or for bat houses mounted on poles or trees, 2 inches longer than its height.
Measure your bat house and drill pilot holes in the rails and house. Use adhesive caulk to attach the rails. Allow the extra rail length to stick out on both sides. Tree and post mounted bat houses should have the rails oriented so that the length protrudes from the top and bottom.
Secure the mounting rails to the bat house using wood screws. Make sure that screws don't enter the living space inside your bat house. They should be in the walls only.
Drill pilot holes in the rails where they extend beyond the bat house. Use screws to attach your bat house to the building, tree or post. It should be firm and should not wobble on its mounts. Leave the area and clean up all human traces, and your bat house should be inhabited soon.