The long-term solution for bats that enter buildings and cause a nuisance problem or present a public health hazard is systematically repairing the structure. Chemical toxicants never solve house bat problems and often create different, more dangerous problems. This section describes batproofing techniques that when used in conjunction with an effective bat box will effectively deal with house bat problems. Recent declines in bat populations and greater appreciation of the ecological importance of bats have led to this solution which encourages bat conservation, protects human health, and permanently solves nuisance problems.

Bats in The House??

Why Bats Become a Nuisance

Bats are usually forced to roost in buildings when natural roosts, such as caves and trees with exfoliating bark are destroyed. Some caves are ruined by flooding (natural progression but often as a result of surface development), dam construction, burning of debris, and ground water pollutants. Cave roosts also are destroyed by explosives used in mining and quarrying, vandalism, and tourism. Deforestation, particularly removal of diseased or old trees with hollows, have also reduced the number of available natural bat roosts.

Bats that have adapted from their natural roost type to human structures are now imperiled not only by some peoples intolerance, but also changes in building construction. Old barns and homesteads fall down, are torn down, or are remodeled, leaving the remaining modern structures tightly constructed with no room for bats.

The general requirements for buildings to be used as bats roosts are known. Colonial bats that live in structures usually occur in areas near water and at the edges of woods where insects are found in adequate numbers and variety. Less understood is the importance of other factors that govern specific site selection such as temperature, humidity, disturbance, and the physical characteristics of roost sites. [More on choosing a bat house site]


Surface development at this commercial cave has caused an entrance to completely collapse shut.

Types of Bat Problems

Bats Outside Buildings

Some bats temporarily roost behind shutters, under wood shingle siding and roofing, roof gutters, awnings, trim with overhang, under flashing around chimneys which has separated or loosened from the solid structure, open garages, patios, porches, breezeways, open livestock shelters, and under sheets of tar paper. Shutters on brick houses are especially attractive as day roosts for transient bats in migration and for bachelor males. In exceptionally hot weather, females may abandon an attic and reside behind shutters. Big brown bats are partial to roosting behind the trim below roofs of houses. Unusual roosting areas include sewers, wells, and graveyard crypts. Generally speaking, this activity is short term, involves just a few male individuals, and largely goes unnoticed. Techniques to bat proof a porch roof will be discussed in the following section on "Maternity colonies within structures."

A Few Bats Inside Living Spaces

The discovery of one or two bats in a house is probably the most frequent problem. The big brown bat accounts for many of these sudden appearances. Common in towns and cities, it often enters homes through open windows and doors, but may use any crevice it can find. This usually occurs in the early Fall when bats are checking for potential roost or hibernation sites. These bats may occur singly, in pairs, or in small groups. The big brown bat can hibernate in below freezing temperatures, so it is common to find them asleep in cold garages, houses or public buildings during early winter. These bats may suddenly appear in midwinter during a warm weather spell and even attempt to feed. Migratory bats occasionally enter buildings overnight during their spring and fall migrations.

Repeated occurrences of bats in your living spaces in mid to late summer suggest that a maternity colony is close by, most likely in the attic. As juvenile bats begin fending for themselves and exploring, one may explore it's way into the your living room. The presence of any bat in your living spaces is purely accidental on it's behalf, and keeping this in mind it is often a simple matter to allow it to escape.

capture1Any bat will usually find it's own way out. The simplest solution to rid the building of the bat is to open all windows and doors leading to the outside. Bats usually will not attack a person even if chased. Never swat or throw linens at the bat, or run around waving. All this tends to do is confuse the bat and leave you exhausted. Above all else, calmly WATCH the bat to make sure it leaves. If the bat refuses to leave, it will calm down and land on something. Drapes and hanging clothes seem to be the preferred rest areas. Place a small box or can over the bat, then gently slide thin cardboard under the "trap" to collect your bat. A more direct approach is to simply take it in a gloved hand then release it outside. All bats can cling to surprisingly small surfaces. For the bat's sake, do not use an overly thick glove when handling, remember this is not molten steel you are carrying. At last resort, local health authorities can be called to collect the bat, though this may result in it's demise. If the bat, or any wild animal, has come in contact with pets, children, invalids, etc. contact your local health department. Health department recommendations vary from state to state.

Occasionally big brown bats may overwinter in a building and arouse during warm weather in mid-winter or early spring. Bats found at this time are usually underweight and need special care to survive. If you find a bat in a building in the winter which must be immediately removed, capture it using a method described above. Keep the bat in a warm, dark, escape-proof container with water, and call a local wildlife rehabilitator.

Need help evicting bats? See our Exclusion Solution...