We had carpenter ants in my apartment right after we moved in here. I told my property manager, and she contacted some pest company and they told her to make sure there is no gap under the sink AROUND the pipes in the wall which there was. She sealed up the gap and I have never had another carpenter ant in my house and we have now been here going on our 7th year. But that is how they were coming in. And we live literally next to a mountain and have tons of trees.