I never noticed any problem with my first ten year of living in my house probably because my bedroom at that time was down stairs. Occasionally I would find a bat flying around and I’d capture it and return it outside. I couldn’t figure how they were getting in the house.
After moving to a bedroom upstairs I learned that my house was infested with bats, and they were mating and living in the airspace between the ceiling and the roof. For quiet creatures they were pretty noisy. It was pretty annoying.
They usually left by the second week of August, so I took matters into hand and began a renovation where I removed the flat ceiling to fix the problem. I vaulted the ceiling and added a sky light. The only place I could see that they were getting in was in a vent which I screened so they wouldn’t be able to get in next year.
It was mid May the next year, and they were back, living in the portion I didn’t vault. I cut a hole in the ceiling of another room and put in a device that emits sounds that supposedly bats can’t stand, but they didn’t leave. When I checked on the device a few weeks later it was covered in bat guano. They were attracted to the sound.
I then put moth balls up there figuring the vapors would run them off. It didn’t. I also spent time outdoors trying to figure where they were getting in. There was guano all over the roof so there was no one place where I could see a concentration of an entry/exit. It had to be something to do with the old roof. It could have been any where. I’ve heard it said that they can slip into a space that one could slip a quarter through.
Eventually it was time to replace the roof and make the siding on the dormer match the siding of the rest of the house that I had just redone. I remove the old comp roof, and the two cedar roofs under the comp roof. One cool finding was that this was on the oldest part of the house that was built in 1925. Under the first roof I found a label from the Arch Cape Cedar Mill. I still have it.
As it all turned out, by re-siding, re-sheathing, re-flashing and re-roofing I was able to eliminate what ever entrances they had been using. The house has been bat free for the last six years.