I'm building an 8x10 freestanding office shed. I used 2.5 sheets of non-T&G 3/4" plywood for the subfloor (I know this was not a good call but there's a plywood shortage in my area). I glued it down with PL400 and screwed it to the joists (most are spaced 16" and the rest are 12"). However all the seams fall halfway between joists, since I unthinkingly placed the half-sheet on the wrong side (I've been kicking myself over it ever since!).
I've already put foam insulation between the joists and it would be extremely challenging to add more joists from underneath.
I'm worried about movement and the edges "sawing" together. The floor will eventually be covered with T&G pine.
How can I keep the plywood from flexing? I'm thinking of cutting the edges of the plywood back to the joists and replacing them with 16" wide pieces of plywood. I would have 2 seams for every 1 seam but at least they'd fall on joists.
Buying T&G plywood is unfortunately not an option.