You will likely have to slope and membrane the whole floor. The Nobel Company has some construction details. Nobel.com This will involve cutting out the joists in the bath area and lowering the whole floor by a couple inches; or have a large buildup at the door. Obviously the former is preferred.
I think the best product for this application is Kerdi, which is a membrane that is applied on top of the setting bed, unlike most membranes which are applied below the setting bed.
Boris
“Sir, I may be drunk, but you’re crazy, and I’ll be sober tomorrow” — WC Fields, “Its a Gift” 1934
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The whole floor does not need to be sloped ( only the wet area) however the whole floor does need to be"in the pan."
Laticete has another product for this purpose. Function is similar to those mentioned above, just a dif application process.
What your beam and joist spans and spacing need to be known before we can tell you what is the best way to go. Also what is the wet area dimension? Do you have access from below and if you need to lower the floor what impact will it have on the space below?
Location of drain will impact on the slope and direction and therefore thickness issues. Do you have a design yet?
F.
The floor joist are treated 2 x 8 16 in on center . The beams are spaced 9 ft apart . The addition is 24 x 48 ft . The bathroom is 8 x 12 ft. There is a 3 1/2 ft crawl space.