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By constructing and properly placing a bat house, you can lure one of Nature's most voracious insect predators to your garden and backyard. Here are some general guidelines:
Building the House
Material: A combination of plywood and cedar works best. Plywood is lightweight and available in big, workable sheets. Cedar is thicker for support and already dark, which eliminates any need to paint. Use the plywood for the front, back, and top of the house; cedar for the sides and partitions.
Dimensions: Typically, a bat house is about 14 to 20 inches wide and 24 to 32 inches tall with a 3-inch landing pad, or floor, extended below the entrance. Place enough partitions—one-half to 1 inch apart—to create 3 to 4 chambers.
Texture: Bats need rough textured wood for the inside walls, partitions and landing area so they can get a grip and easily climb about. If the wood is not rough hewn, you can create the right texture by sanding the wood with coarse sandpaper.
Paint: Cover the outside of the house with two to three coats of latex paint to protect it from moisture, air leaks and wood deterioration. Paint also helps retain heat in the cool months. Caulk all the seams (especially around the roof) to keep your house draft-free. Do not paint or varnish the inside of the house.
The paint color can range from deep brown to white, depending on your climate and the amount of sun exposure hitting the house. Warm colors absorb heat; light colors reflect heat. (See Heating/Sunlight below)
Ventilation: If July temperatures typically exceed 85 degrees F where you live, cut out vents 6 inches from the bottom of the house. Make front vents as long as the house is wide; side vents 6 inches tall.
You can also buy bat houses at hardware stores and from gardening catalogs. This is a good choice if you want a bat house but don't have time to build one.
Choosing the Site
Mounting: Attach the house 15 to 30 feet up a telephone pole, tree, or side of a house. Anchor well so it won't come down in a strong wind.
Heating and Sunlight: Make sure the bat house gets 4 to 10 hours of direct sunlight daily to provide warmth. Ideal daytime temperatures inside the house should be between 80 to 96 degrees F. If you live in a hot climate, the house needs less sunlight than if you live in a cooler climate. In moderate climes, face the house in southerly direction to provide a combination of morning sun and afternoon shade.
Water: Bats need to drink every night and prefer to roost within a half mile of water—preferably a stream, river, or lake.
Tips
Most houses become occupied in the first or second season, especially if bats are already present in nearby buildings. If your house is empty after that time, move it to another spot.
Install your house before early April when bats are migrating and looking for roosting areas.
To determine if bats have taken up residence, look for droppings (guano) on the ground below the house, shine a flashlight into the house during the day when bats may be roosting, or simply watch in the hour before sunset to see if they emerge from the house.
