I have a deck 8 ft high with 6x6 posts. One section by the garage has a span between posts of 19 feet. It's starting to sag, because the builder used 3 2x 10's but 2 of them are pieced in and bolted. My question is, what is the proper lumber to span 19 Ft. The beam is 5 Feet from the ledger and the joists are 2 x 10 spaced 8" apart.