R:


Well, I must respectfully disagree. In addition to assurances from folks
here WHO HAVE DONE IT, as stated in my OP, I have walked on a floor made
with 2 X 10's spanning 16 feet. There was no bounce. Surely I can go
to 2 X 12's and span 4 more feet.

The chart you pointed to is neat !! Thanks !! It does indicate I would
have to use 12 inch centers.

--James--




I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Choose US species and the loads you indicated - you can't span 20'
easily or even barely. Your house, your call.

R