Successful bat houses need at least 2 feet of height. Cedar is an excellent building material for bat houses and needs to remain rough or textured to allow bats to grip it.
The minimum dimensions for a successful bat house are 24 inches high by 13 inches wide by 3 inches deep. The interior needs to include several different chambers with grooved or roughened wood. Rocket-box-style bat houses need to be at least 3 feet high to be successful. A small air vent roughly 8 inches from the bottom of the bat house provides good temperature regulation as does adding an internal ceiling under the roof of the bat house. The rear wall of a bat house should be slightly longer than the front to provide a landing area for the bats.
A simple bat house design consists of a roof and four walls, using the previously mentioned dimensions, with several interior chambers. The bottom of the bat house is open to allow bats to enter. Rocket-box-style houses consist of multiple shells mounted on a pole. Between each shell is enough space for bats to roost. Bat Conservation International provides excellent free bat house plans to aid in construction.
Bat houses require seven hours of sunlight but should not receive direct sunlight all day long. It is a good idea to install a bat house near a permanent water source.