James writes:

I was wondering if a person could use 2 x 12s, and span up to 24
feet
without supporting posts? I doubt it. Yet, I walked up into the
loft 2nd
level and jumped on the floor (I weigh 200 lbs), and the floor felt
"pretty" solid. Not rock solid , of course. Of course, going to 24
feet
would be 8 more feet of span, and could make a big difference

Forget dimensional lumber and use TJI framing. Engineered I-joists
will do any span you want, cheaper than lumber, and they are lighter
and easier to handle.

Larry