Increasing Bat Populations
It is often difficult to attract bats to an area and as you are probably aware many species of bats are currently declining in number.
Bats in Pennsylvania are insect eaters so you do not want to use any insecticides that would reduce their food source. Bats are attracted to water so if you have a pond, lake or stream that is a plus. Bats will use bat boxes for roosting so putting up boxes can also help. Females form maternity colonies that roost in barns, buildings, and boxes but they are very site faithful and often difficult to attract unless they are being excluded somewhere else nearby.
The publication A Homeowner's Guide to Northeastern Bats and Bat Problems has general information on bats and bats inside the home, and includes bat box designs. More information on attracting bats and dealing with bat problems can be found at the Bat Management and Conservation website.