- somebody needs to answer the 305.8 aspect. If the plumber broke code... case closed.
- punching through the back of plywood with your fastener, actually does increase it's holding power somewhat. It's a marginal increase, but it's there. Don't believe me? Find a structural engineer who works with wood a lot, and ask him/her.
- are you guys seriously trying to tell me that you've never seen a nail or screw protruding through a subfloor before?
- For wonderboard screws, 1-5/8 is the most common size, by a HUGE margin. I've seen people post threads, on DIY forums, asking if other sizes even exists. I can't get 1-1/4 at my local hardware stores, or the big box stores (which is fine, since I prefer lumberyards, anyways).
- This was totally forseeable. If my plumber was running lines that close to the subfloor, I'd have him change it. I honestly can't imagine him doing it, though; he's good about remembering the next guy.