I am confused with "deck tables" from different sources, specifically concerning beam size for a deck.

I am planning a basic deck as shown:

Attachment 9677

Sources that describe the "tributary load" and "tributary length" would allow me to use as little as (1) 2x6 for the "front beam" (tributary width = 3', not even on the charts) and (1) 2x10 or (2) 2x8's for the "middle beam."

Attachment 9675
http://buildingcodes.jocogov.org/doc...eck%20Book.pdf


More generic tables that just describe "beam span" would call for much more support: (2) 2x8's for the front beam, and (2) 2x10's for the middle.

Attachment 9678
Deck Tables - Deck Building Tables - Building a Deck Tips and Tricks


The "engineer" in me says I am interpreting the tributary load concept correctly, the first set of beam calculations is adequate, and the front beam is only supporting about 1/2 the load as the middle beam.

Any enlightenment would be appreciated.

The center beam carries half the load, the front beam and the connection to the house each carry one fourth of it.

Me I would get rid of the whole center row of posts, put a double 2x10 on the front and use 2x8's for my joists. I have built barns this way holding up tons of hay.

thanks for the comments

My main goal is to understand the tables so I can design a deck that follows typical building codes.

I actually have a reason to keep the front beam a single 2x; I am extending the posts up for a sun cover, and do not want to notch the post more than once to keep the thickness. There is not a lot of info out there on this, so I am playing it safe.

You can just use taller posts, place the double 2x one on each side of the post at the elevation for your deck, then place the suncover support attachment further up. If you have trouble finding posts long enough, use a post that comes up to the double 2x10, place the 2x10s sticking up an inch or two above this post. This will form a nice little pocket for you to drop your second story post down into and hold it in place by nailing the 2x8 joists to the side of it.