The installation of the hardwood floor is not the problem, the sub floor is my concern. The current sub floor is 3/4" pressboard and my understanding is that the nails used to install the hardwood will eventually let go if installed using the pressboard. I will be using 3/4" plywood as my new sub floor, but do not want to lay the plywood over the existing sub floor. My question is how do I remove the current sub floor without damaging the walls or structure. My first thought is to use a circular saw and cut around the room using the baseboard as my guide.