Bats’ steady consumption of insect pests makes adding a bat house to your yard not only good for bats, but a smart choice for you. Of the 40-plus bat species native to North America and Canada, there are 14 that typically will make themselves at home in human-installed bat houses.
You can install bat houses year-round, wherever you live (weather permitting), but getting houses up in preparation for locally hibernating or returning migrating species is best completed in the fall or winter. That will give building materials—ideally cedar or untreated exterior grade plywood—a chance to “air out” before bats begin a spring search for a place to roost.
Bat House Basics
Whether you choose to purchase a prebuilt house or build one of your own, there are basic acceptable standards for building and installing constructed bat habitats.
Bat houses may be single chamber or have multiple chambers. Multiple chamber habitats and rocket-type boxes will be more conducive to nursery colonies of bats.
Bat houses may be tall and wide (minimum 20 inches tall and 14 inches wide) and mounted on building walls or back-to-back on poles. You may instead choose to install a pole-mounted rocket box design (at least three feet tall) that has a continuous 360-degree chamber. Ideal crevice size within the houses is three-quarters inch.
A three- to six-inch landing area extending below the backboard entrance is necessary, and both the landing area and the inside surfaces of the bat house must include bat footholds. Roughened wood or wood horizontally scored at quarter-inch intervals will suffice, or eighth- to quarter-inch plastic mesh can be installed as long as it has no rough edges and is fastened tightly enough to remain stationary.
Construction should be gapless with caulked or glued exterior joints to prevent drafts. Hardware should be exterior grade and should not extend into the house.
Half-inch ventilation slots are necessary in all bat houses unless you live in cooler climates. These vents are ideally placed no more than one-third above the house’s bottom. Front vents should extend the width of the house.
The temperature within your bat house is important, and the exterior color you paint it affects the temperature. In general, the cooler the climate, the darker the color. Black is recommended for bat houses in Canada; for the United States, consult this color recommendation map.
Bat houses should be mounted 12 to 20 feet above the ground (or the top of the vegetation beneath them), and 20 to 30 feet from neighboring obstacles. Building-mounted houses will do better under eaves where they are better protected, and should be mounted facing east or south where they can get six to eight hours of sunlight daily. In colder climates and those with great fluctuations of temperature, building-mounted houses are a better choice than pole-mounted houses.
Habitats placed near diverse and natural vegetation, forests and a natural water source will be most successful. Bat houses should not be mounted in trees because of predators, excessive shade and obstructed access.