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 (http://rds.yahoo.com/_ylt=A0LEVIYbqV1LHnsBiwoPxQt.;_ylu=X3oDMTExN3Y1YzI 1BHNlYwNzcgRwb3MDMQRjb2xvA3JlNAR2dGlkAwRsA1dTMQ--/SIG=12avjr2rs/EXP=1264515739/**http%3A//www.ilevel.com/floors/f_MicrollamLVL_beams.aspx)

Education - LVL (http://rds.yahoo.com/_ylt=A0LEVIYbqV1LHnsBjwoPxQt.;_ylu=X3oDMTExdGs4NWh xBHNlYwNzcgRwb3MDMwRjb2xvA3JlNAR2dGlkAwRsA1dTMQ--/SIG=1233qgej0/EXP=1264515739/**http%3A//www.timber.org.au/NTEP/menu.asp%3Fid=103)

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