Rabies Prevention in Washington State: A Guide for Practitioners
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Batproofing

How to prevent bats from establishing a colony in a house or other building: Bats can be kept out of buildings by closing or covering openings that allow them entry. Attic and soffit vents should be screened with 1/4 inch hardware cloth or screen. Other openings, such as gaps in siding, spaces under warped fascia board, and loose flashing and moldings should be sealed, too. A variety of materials may be used, including sheet metal, wood, plaster, caulking compounds, polypropylene bird netting, and fly screening. Keep in mind that bats can pass through crevices as small as a dime. Before batproofing, make sure that there are no bats already in the building.

House
Figure 6. Common points of entry and roosting sites of bats (courtesy of Dr. Stephen Frantz, New York DOH)

How to exclude bats that are present in a house or other building: Bats give birth in the summer, and the offspring do not fly until they are almost full-grown (usually by August in Washington). Therefore, to avoid trapping helpless bats inside a building, do not attempt exclusion from May through August. To exclude bats that have settled in a building, try the following:

  1. Observe your building on 3-4 successive evenings (at dusk) to identify the exit (and likely entrance) openings the bats are using. These openings are often indicated by dark staining around and droppings beneath the site.
  2. After you have established where the bats are exiting and entering the building, seal all openings (as small as 1/4" wide) that the bats do not use. Sealing materials are listed above. Openings between the roosting site and the occupied portions of the building should be sealed first.
  3. Next, secure plastic one-way tubes over the exit holes used by the bats (see figure 7). Bats will leave but will not reenter through these tubes -- they have great difficulty crawling or climbing up smooth, collapsible plastic.
  4. Leave the plastic one-way tubes in place for about one week to ensure that all bats have left the roost. Returning bats may fly around the openings for the first several days, but will eventually find a new roosting site elsewhere.
  5. After it is clear that all bats have left the roost, remove the plastic one-way tubes and seal the remaining openings.
tube preparation Go on to the next step. the one way gate - a plastic tube Go on to the next step. bats exiting one-way gate
Figure 7. How to make a one-way gate.

Excluding bats from a building is often difficult and time consuming. Contact your local health department for a list of pest control companies that do bat exclusion work in your area.
This monograph was produced for the World Wide Web by the Northwest Center for Public Health Practice in cooperation with the Washington State Department of Health. See references for further acknowledgements.