Barriers to entering the house
The best method to exclude bats permanently from a structure is to prevent their gaining entrance. Locate any potential or current openings the bats are using and temporarily seal them while the bats are out flying at night. The seal can then be made permanent at the homeowners' leisure. Sealing the openings should be done before June 30 or between August 15 and September 15 to avoid sealing in baby bats or hibernating adults.
To locate the openings, watch each side of the house from sunset to 1 hour after sunset or until the bats are seen leaving. As an alternative, watch 1 hour before sunrise. Watch only on warm, still evenings or mornings because the bats will not leave the roost in inclement weather. Other alternatives include illuminating the inside of the roosting area at night and observe where the light can be seen from the outside.
Openings are usually found behind chimneys, under eaves, soffits, ventilators, and door and window frames. Seal all openings of 1/4 X 1 1/2 inches or openings of 5/8 X 7/8 inch or greater. Seal with masking tape, duct tape, fine steel wool, fiberglass insulation, caulking, or hardware cloth.