Expert: Stephen Major (Owner--Major Design Group) - 4/29/2007

Question
We are installing a shower pan and had removed the old sub floor.  What are your recommendations, should we put sub floor under the new pan?  Needless to say currently our bathroom is completely stripped.

Answer
Bonnie,

I assume that you are referring to the floor underlayment rather than the structural subfloor.  The actual subfloor is the structural plywood or boards that are directly attached to the joists, and never removed in a typical remodel except for rot.  

Normally I would mount the shower pan to the subfloor and then bring the new underlayment (and of course the finish flooring) up to meet it.  It will end up being somewhat "buried" in the floor when you are done.   The best way to mount a shower pan is to mix up a batch of latex-fortified thinset tile mortar and ease the pan down into it.  Level the pan and nail or screw it in place by the flanges.  The thinset will set hard and its adhesive properties will bond the pan to the floor, eliminating movement and squeaks.  It will also cause the pan to be a little high (1/4" to 1/2"), which is a good reason for not installing floor underlayment (whether it's plywood or tile cement board) afterward.

Be sure to caulk the finished floor to the face of the shower pan when finished.  

Good luck and let me know if you have additional questions.  If you wish you can send photos of your progress and completed project to my e-mail for possible web publication.  info@majordesigngroup.com

--Steve Major