I have a 18'7" x 20' two story room. Going to add a room over this room. We will need to span 18'7" width with 2x12s on 12" center. Will this support the new floor on second level, with furniture and a television, as described. It is better to go an engineered flooring system, double up the 2x12x, or double up to form a girder with 2x12, then plywood in betweed, then 2x12 again?

If girders, could they go to 16" centers. Want to do it once and do it right.

I would look into LVL's for the supports,they carry great loads and have little deflection.

Versatile Beam for Residential Construction - iLevel Trus Joist Microllam LVL Beam

Education - LVL

We used these for a clear span of 22 feet and have had no problem with them.