Loft Floor Joist Size - timber options

[Tony(Guest)]

On the 20'x30' 1.5, we are looking at different loft floor joist size options as we want an exposed timber look.  We plan on a t&g wide plank floor on the loft.  What sizes of beams are people using?

Also, I was looking for a span calculator for use with 4" wide timbers but have only found calculators for 2" wide lumber.  Anyone know of a calculator for wider timbers?  

On another project, I am wanting to use 4" wide timbers on a span of 12', what are my options here?

[John Raabe]

The loft floor plan for the 20' wide 1.5 story has an option for a beam and deck ceiling using Dbl 2x12 or 4x12 at 48" with 2x6 T&G on top.

Get a copy of Charlie Wing's "From the Ground Up" as it has good charts for sizing rough cut and dimensional sized timbers.