I have a 1970s house with 1.125" plywood subflooring over 4x6 joists 48" on center. It's pier and beam over a crawlspace. How sturdy is this subfloor? Is it common? Can it handle most types of flooring? Frankly it doesn't "feel" all that sturdy, but it has lasted 30+ years. I'd like to strengthen it in some of the larger rooms and am wondering if I can just add another layer of 3/8" plywood and then some nail-down hardwood flooring. Is this sufficient? Thanks in advance!