Your pretty safe with lathe boards, wall studs and floor joists from demolition jobs. Anything that was exposed flooring most likely has some kind of varnish on it.Thanks for the advice just found out the deer camp has about a cord of last years ash left and since it's a open fireplace im going to swamp some out and i have been collecting scraps of building sites were my stepdad builds houses..and how would old oak hardwood floors burn in a non cat i just tore out alot of floors