Now that the beams were on the 1st floor, properly spaced and measured, we could
start on the sub-floor.

Turned out we didn't have the proper boards for the radiant heating we had planned,
so this sub-floor involved ripping down 1x6 into small strips, and ripping the tongue off of
every other tongue and groove.  It took a week to complete this step, but the results are
quite good.