Q&A for How to Build a Bat Box

Bats always fly into their roost but will walk out if they must. Therefore after the bats have left the roost in the evening, hang a tarp loosely in front of the opening where they enter the roost. After a few days the roost should be empty and you can make a permanent repair. Avoid doing this in the spring when they may have defenseless infants. Also, remember that it is illegal to kill or molest bats.

It's often the back plate/wall of the bat box which is longer and lower than the front of the box. It can have grooves cut into it, allowing bats to use it like a ladder to climb into the box.

The inner partitions can be made of thinner material. It's just simpler and quicker for most box builders to cut every piece from one plank, as it is the same width and thickness for ease of assembly. Make sure all timber is untreated, and that the external structure is thick enough to provide insulation.

Not sure that "horizontally" is the correct term here. The box needs to be secured so that the bottom opening that the bats use to enter and exit the structure is parallel to the ground and perpendicular to the mounting surface.

Some species hibernate during the winter, while others will head south. Usually, they'll follow the food supply, so if there aren't a lot of insects during the winter, they'll fly elsewhere.