I am the bat expert---should be since it cost me over $1000 to get rid of them. Bats can get in a hole about 3/4inches wide and a #2 pencil high. We have a fairly new house but the builders left a few spaces that weren't sealed up. The "bat man" came out and trapped (one way traps) those that were leaving. Then he had to caulk all holes, had to go up (dressed and covered from head to toe wearing a respirator) to get rid of the bat feces. Unfortunately, he never had to have any repeat visits to any house.....we were just "special." He had to come back 3 times. Oldest son killed one with a tennis racket. "BRAVE" husband sat in safe room leafing through the phone book for an exterminator. It sounds funny now,,,but wasn't then.