Need Help on Beam sizing/pier spacing

[louky]

I am building a 12 x 16 shed using info gleaned from this site.  My plan is to use the pier blocks on pavers over packed gravel 18" deep, soil is clay, seems to drain ok, located in Southern Indiana. I will be using 2 x 6 treated floor joist, 16" on center, with the floor joist cantilevered 2' over each beam, leaving an 8' span between beams.

My question is about the beam size and pier spacing.  I have already dug the 4 corner piers, on an 8 x 12 grid.  The beams will also cantilerver 2' on each end, leaving (now) 12' between the piers on the long side.  If I add 1 more pier under the  beam, it would be spanning 6',  if I add 2 piers, the span would be 4'.

I would be using either doubled 2 x 6 or doubled 2 x8 for the beams?.

Your answer may save me from digging 2 holes  

Also, is there any suitable way to build these beams up from shorter stock?  The lumber I've seen in 16' lengths lately has been pretty bad.

Thanks in advance

[John Raabe]

You need to engineer the beams and posts and foundation pads by starting at the roof and doing a load trace. Snow load and soil bearing capacity are the two variables that can be plugged into the calculation. Then, of course, there are several ways to structure the beams and post connections.

For a few hundred dollars your local engineer can design this for your layout.

For simple structures most folks buy an inexpensive stock plan and use it for the foundation layout if nothing else.

The 12' x 18' Little House plan could be easily shortened 2' and there are notes in that set for using built up beams. (Basically stagger the joints a min of 4' and nail and glue well.