Where they are appropriate you might try placing bright lights, since bats strongly prefer to spend their days in darkness. This may be most likely to be tried in buildings that are difficult to seal, such as warehouses or large barns. Where possible, permanent closure of openings will always be the best method and offer the longest control.
So, let's look at the steps you should take in your bat control program, and these four important steps are:
Bats usually enter structures through openings that are well above the ground, so it will be very important to check the roof and the eaves, as well as vent openings leading into the attic. They are not capable of chewing material away to create an opening, as rats easily can do, and so they must use existing holes. However, it does not take much, for a small species of bat can squeeze through a crack only ¼ inch wide, or a hole that is about ¾ inch in diameter. If there are lots of bats then they likely have found openings larger than this. One excellent way to determine where these are is to go outside in the evening, sit down in a lounge chair with a cup of hot tea and a pair of binoculars…….and watch. You may substitute hot chocolate if you are not a tea drinker.
Places to suspect might be where power or phone lines enter the structure through the walls, where holes have been punched for plumbing pipes or TV cables, possibly around roof-top vents and louvered fans, and around window framing that may have developed gaps. Wood shake roofs or tile or slate roofs may allow the bats entrance if there is not full sheeting under these roof materials.
You may find bat droppings on window sills or porches outside, and wonder if this means that bats are entering the structure above that point. This probably is not the case. Instead, what you likely have discovered is a site where bats will land to feed on their catch, clinging to the wall or some other object they can grip as they consume the bugs. They then defecate and move on. This may make you a little squeamish, but it is important to determine if the little black pellets you have found are from bats or from rats or mice, for they look very much the same. The difference is that bat droppings are shiny, and if you press on them with a stick they will easily crumble into little pieces.
Openings that you find that you know the bats are not currently using should be closed right away, so they won't find these as alternatives once you have closed off the ones they currently use. Depending on the size of the hole and what kind of surface it is on you may use several options for this. For small cracks and holes a simple caulking gun and tube of caulk will work wonderfully. Vent screens should be replaced or repaired. Larger holes could be covered with metal sheeting, hardware cloth, or plywood. Unusual holes that are hard to cover in this manner could be filled with expandable foam, available in aerosol cans. A temporary fix could be done quickly by pushing in a wad of steel wool or copper mesh.
Holes that you identify as definite pathways for the bats should not be permanently closed right away. You would like to give all these unwanted residents of your building the opportunity to depart first, so some sort of one-way door needs to be placed over that hole. Just picture a "doggy" door that only goes one direction. The flaps could be made of sheet metal, wood, plastic, or stiff netting, but in all cases it allows the bat to push its way past the door to exit, but prohibits re-entry. These should be left in place until you are sure all the bats have left the building, usually in less than a week, although this will depend on the weather. If you are having extended rains the bats may just stay secluded until the weather is nice again and their foods will be flying.
Another one-way door that is used is a tube of heavy plastic sheeting, allowing the bats to go into the tube and work their way out of it to fly away, but they cannot return through the collapsed tube. Once you are sure your extended visitors have moved on the flaps can be removed and a permanent repair can be made to close off the openings. All of these methods ensure that you eliminate a well-documented health problem without harming the animals.
Bats that have resided within a structure for a period of time may be very determined to get back into it, so you need to spend time after the exclusion job simply observing the exterior. Watch for bats gathering near the sites they used to enter through, or for bats entering new, undiscovered openings.
A side benefit to this exclusion for bats is that it is also exclusion for most other kinds of pests, including insects, rats, spiders, etc. The wonderful array of unwanted house guests relies on finding hidden entrances to your home or office building, and the repair of these openings will be of great help in keeping them out.
This is a very important step, but it must be undertaken carefully. If there is a large accumulation of bat droppings, and therefore likely a lot of urine has fallen too, this can pose an ongoing health and odor concern for you. It needs to be removed. This can be a major undertaking if the bats were inside walls or other areas that need to be physically opened up, so contracting with a professional could be needed.
Whoever is chosen to manage the clean-up, though, needs to wear protective clothing, and this includes eye protection such as goggles, long sleeved shirt and long pants, rubber gloves, and - very important - breathing protection. The worst hazard would be for someone to inhale the dust stirred up in a cleaning process, for bacteria and viruses growing in this nutritious medium are then taken directly into the body. The proper protection would be a respirator that uses air-purifying cartridges, and the cartridges should be "HEPA" filters that are capable of removing the tiny pathogenic organisms from the air. Following the cleanup all clothing should be either thoroughly laundered or disposed of.
To reduce any chance of creating airborne dust that is contaminated the area should first be dampened with a disinfectant solution. Suggested materials have been a 1:10 solution of bleach, or a household disinfectant used according to its instructions. Washing things frequently to avoid dust and spread of contamination is important, and a very important rule is never use a vacuum cleaner to remove rodent, bird, or bat droppings. The filters in vacuums do not retain the pathogens that are now blown out the back end and are easily inhaled.
As you can see, bat exclusion can be a difficult and time-consuming process. Before you begin you should consider contacting a professional company with experience in removing and excluding animals from buildings. They will have the knowledge and equipment to take care of the problem in a manner that will prevent you from having to expose yourself to the difficulties and possible health consequences.
And finally, try to avoid doing exclusion work in the summer, say from the months of May through August, as it is very likely that young bats will be in the building at this time, unable to leave, and will be trapped inside to die.