I'm in the process of buying a 1953 cape that has very old worn asphalt shingles in need of replacing. From what I can see in the attic, there are no leaks or rot in the tongue in groove planks and it looks in fine shape. Assuming no rot, would it be advisable to still put plywood on top in order to assure that the new shingles nail securely and not potentially on a joint in the tongue in groove? I want to do this right, but like most people, have a budget. I will be doing most of the work myself with guidance from an experienced carpenter friend who suggested the ply - just looking for another opinion.