Bat Proofing Your Home

We encourage hospitality towards bats, however if there is a substantial reason to exclude them this should be undertaken only during the month of May, and from mid-August to mid-October. In between those periods young bats could be blocked inside and the decaying bodies will cause a severe odor problem.

Are Bats Present?

The first step is to determine if bats are actually present. Good signs that they are:

• Distinctive ammonia smell in the house or attic
• Stains and droppings on outside walls of the house. Bat droppings are dark brown, small (3/16" to 1/4" long), and are more oval than round.  

How to locate and block entrance and exit holes

Block openings and put one-way door in place during the day when the bats are sleeping inside. Bats leave their daytime roosting site from a half hour before sunset to a half hour after sunset.

Station someone on each side of the house during that time to watch areas under the eaves, around chimney flashing and louvered vents for exiting bats. It's also wise to check these areas on a ladder for openings that the bats may not be using. 

Once the openings have been located, block all, except one, using: ¼ inch hardware cloth (galvanized steel mesh), wood, or sheet metal. Seal edges well, bats need only a half-inch opening to enter.

Exclusion

The only way to exclude bats and be sure none are blocked inside is to use a one-way door. Here are two one-way door designs from which to choose. Put in place during the day while the bats are sleeping inside and leave in place for three or four days to be sure all bats have exited.

Option 1

This technique uses a flexible plastic mesh purchased at garden centers and used to protect fruit trees from birds. It is called bird netting or fruit tree netting.

Cut and hang the netting so it extends 6 inches beyond the opening on all sides. Using staples or duct tape, attach the netting across the top and halfway down each side, allowing the bottom to hang loosely. 

The emerging bats will be able to crawl out the bottom, but returning bats will be unable to find a way in.

Option 2

Another method is to place a piece of flexible plastic or .045 inch rubber over the opening, making sure that it extends two inches beyond the hole on all sides. You want a material that will allow the bats the ability to push the covering open to exit the hole, but the covering material will fall back into place and fit tightly over the opening so the bats cannot re-enter.