"Art" wrote:

My original post was made 3 am. That is the only explanation for why I
typed sheetrock instead of plywood. Thanks for pointing it out.

Sheets of plywood in the floor are a good way to distribute the load as
well.

In a room with just the spa, take the floor down to the bare sub floor,
glue and screw a layer of plywood.

Plywood can be used as cross bracing from below, since you already know
where the pipes and such need to be run.