Hi, I've looked through all the span tables, beams, etc and I cannot find anything at all that speak to this. I am building a small deck off my patio door, it's going to be 4' x 8' (8' along the house, and 4' out). It's a free standing deck (with deck blocks), I am using 4 posts (4"x4") and was planning on using 2x10s for the beams (beams will span 4' (so perpendicular to the house). I was planning on notching the 4"x4"s and then connecting the 2x10s with structural screws. Then I have 4 joists (parallel to the patio door) sitting on top of the two beams at 16" apart. Anyway, this is the info I submitted to the city, they gave me a permit. However, would it be better (more solid - less bounce) to replace the 2x10 beams with sistered 2x8s, sitting on top of the 4"x4" posts? for the 4' span, would this make any difference, or would it be negligible? I can't find any table to give me this sort of information, most beam calculators and tables have sistered beams. Any help would be appreciated. Thanks!

As you can see in the photo, one of the supporting beams of my balcony has "dry rot." 1) I plan to cut away the rotten wound and replace it with new wood affixed to the remainder of the existing beam. Any thoughts spring to mind? (type of wood, what not to do, etc...) 2) How do I prevent this from happening again in the future? - Obviously painting it - any particular type of paint? - Boron wood injections? - Some kind of sealer? - Some kind of plastic covering or layer under the floorboards of the balcony? - Anything else?