Deck will be off the house ten x twelve feet and six feet off the
ground.
I plan on using cones four feet into the ground, I figure a little
more then five bags of concrete per hole.( It is in a hard to get area
a concrete truck out of the question.

My question is what is the maximum length I can go using 2 x 8
pressure treated joists between 4 x 4 pressure treated collumns ?