Among the biggest problems that includes having a colony of bats roosting in a building is the massive quantity of waste, or guano, left behind. Bats eat plenty of insects, and have a high metabolism, and every bat poops 20-30 times every day, leaving behind a whole heck of a great deal of bat poo! These are the primary reasons you need to clean up the guano following the bats are gone:The guano can develop a form of fungus that can cause the lung disease histoplasmosis in humans.The droppings just plain smell bad, and in volume, have an odor that may overpower the house. The droppings and urine are corrosive to metal and wood, and can compromise the structural integrity of the construction. In a nutshell, the wood can rot. The droppings and the scent will lure in different animals and insects - that I often see hundreds of cockroaches crawling on bat guano.
Step 1: Make sure the bats are all removed, and the building is sealed so none may return in. Step 2: Remove loose droppings on smooth surfaces by vacuum cleaner and wash such surfaces using an enzyme-based cleaner. Step 3: Remove all soiled insulation - you are not going to have the ability to clean it. If it is not too badly soiled, you can simply spray it with the cleaner. I use an electrical atomizer, and an enzyme-based cleaner. There are numerous brands, but I have been using Bac-Azap. Bioshield is good also. The fogger makes sure that each nook and cranny is covered.
According to each bat leaves 20-30 droppings daily (depending on time of year and how much it eats, of course). If you have a colony of a thousand bats in your attic, multiply 20-30,000 bat droppings times the amount of bats that are in there, although the droppings are small, you can end up with a enormous buildup