Stripped the old 1962 vintage pink 5x8 bathroom down to the studs. I have plumbers coming tomorrow to install new hot and cold shut-offs (sink and toilet), move the shower head up the wall a bit, install a new valve, and complete the bath tub hookups.

Though my question may be more structural in nature, as opposed to plumbing-related, I thought I'd start with this forum.

The original sub-floor in this bathroom is diagonally-run 1/8 planks over 2x12 joists, 16" on center. We're laying down 15/32" OSB over this, to provide the ideal surface for the incoming Schluter Ditra membrane and ceramic tile. It stands to reason that the OSB should be extended to the area where the tub will go, to further reinforce this section and provide adequate support for the added weight.

The tub is a jacuzzi acrylic 3-wall alcove unit with a built-in apron. The manual states that the flooring underneath the tub must be able to support ~56 pounds per square foot. Impossible to tell whether or not the planks and joists will support that level of weight, as is, but am I right in thinking that an added layer of OSB can only improve the amount of support?