I read the post below with interest and was wondering if there's anywhere online to calculate max. spans and such. While reading I realized that my upstairs has much larger spans with 8" boards, but they are 3" (actual) thick oak, 24" O.C. Curious what something like that can span as there is no deflection of the floor and it feels like it's a brich $$@! house when you walk on it. I'm going to be doing some drilling/knotching into the joists when I run some plumbing and had planned to sister them for strength. The 1st floor has 14" round beams for floor joists that are just a joy to work around, LOL!