we found out from spotting wasps flying in and out of our roof, just under the tiles. I didn't want to go up to the roof to check it out, but was watching the spot for a while and knew that wasps were traveling in and out of a small crack. We called the company and they came to check it out. Sure enough a wasp hive was building their colony inside our roof. The guy sprayed some white powder into the hole, covered it up with a garbage bag, and promised that would be the end of it. If not, he would come back to fix it for free. He was right, and the wasps never returned.