I discovered my "2x8" floor joists are actually 7&1/4 and many actually 7" with NONE at 7&1/2 that one would expect. The span is 13 feet and the floor is "bouncy". My idea to increase rigidity is to add another two and a half inches to the bottom of the existing joists using a 2x3 attached with waterproof glue and screws. If you think I might benefit from this tactic, please offer advice on glue type and screw spacing. My plan would be to use 2x6's ripped to 2&3/4" with pre-drilled screw holes. About Me: I've been a do-it-yourselfer all my life with limited experience removing weight-bearing walls and substituting self-built laminated beams from plywood and lumber. I also owned and operated a small woodworking shop for a few years where I did complete kitchens and baths along with custom, built-in office furniture.