1 1/4" is the recommended thickness of the sub floor under ceramic tile.
That could be 1/2 +3/4.
Ripping up the existing 1/2" is not a good idea. There will always be an
edge with no support under it. If there is no damage to it leave it, vacuum
it real good, screw (make sure screws are long enough and go into the
joists) and glue 3/4 right over the top.
Screw and thinset the cement board to the new 3/4 ply.
Hardest part can be raising the toilet flange to the new level.
"DaddyMonkey" wrote in message
...
Thank you for reading my post.

I want to know if I should pull-up the entire sub-floor of my guest
bathroom.


My house is a 1982 tri-level (kit?). 50 foot x 25 foot. Most floor &
ceiling joist are 24" OC. The joist run the width of the house.

The guest bathroom (full bath) had a tile floor on a mortar bed, that I
removed.

The sub-floor that's under this tile floor is 1/2" plywood with some
sag on the outer ends and very springy between joists.
Is this normal after removing a mud-tile?

I ran a "stud-finder" along the floor, and
found that the joists are NOT 24" OC and more like 16"OC it a
hit-and-miss pattern... (guest bath is in center of the 3rd floor/
Master bath is on opposite wall of guest bath.) Is this ALSO normal?


~BUT~ my question IS ....
Should I set my circular-saw at just under 1/2 inch, and THEN replace
the entire floor.... or should I just add exterior-grade plywood over
the exisisting sub-floor?

For more information... the "basement" (1st floor) Den, 1/2 bath and
office are 8 foot ceiling, but the basement hallway is 7 foot.
(Bunch of duct-work, plumbing. ect.)


Thanks,
Dave