Repair bathroom tile floor
I've inherited a brick duplex built in 1957. On one side the tile bathroom floor is cracking. Part of it has dropped down about 1/4 inch. When I looked underneath, in the crawl space, the tile is laid on an old style bed of mortar. A board supports the mortar base, and this board is supported on each side by 2 x 2s nailed to the joists.
I think the problem is that the board supporting the mortar base is sagging. Wondering if I could install a new board underneath the old, and support it with jack posts? The floor joists are 16 inch on center.
Will appreciate your advice. Thanks!