One final observation. Based on the above discussion, I believe that carpenter ants can and do nest within structures. This does not mean that they will not forage into structures from surrounding trees. Carpenter ant control becomes more difficult because one must determine if the nest is in the structure or outside. If it is outside, it is probably easier to find and treat than if the nest is withing the structure.
Carpenter ants are most active late in the day or early evening.
Inspections should coincide with this period of activity. If a discussion dealing with pest control goes for very long, the topic of pre-treatments soon finds its way into the conversation. Pretty soon someone will say that x company is charging eight cents per square foot or six cents, etc. Or that a company is driving from somewhere in another state to do a treatment at a government facility, in let's say, Columbus. Or that a pest control professional driving a small pick-up with a 100 gallon tank arrives at a treatment site containing several thousand square feet of treatable surface.