I don't use treated lumber at all in my kennels or dog houses. The newer stuff is not as bad but the older chemicals they used to treat lumber was carcinogenic. Either way, no treated lumber. I think both my labs must be part beaver the way they chew wood. I have their houses in the kennel I have now and had to put drywall edge on all the wood edges so they did not chew them off. My female is a hard-core nester that digs at everything she lays on.