Waterproofing Shower Wall Cavities and Subfloor
We are building a new home in CT (climate zone 5). In the bathrooms, we have chosen to go with one-piece fiberglass tub/shower units with cultured marble panels on the walls above the unit. I am very sensitive to mold, so we plan to moisture proof the walls and subfloor prior to installation. I see lots of information related to tile showers, but what is the best method for waterproofing behind and below a one-piece fiberglass unit? We will be doing a pre-drywall blower door test. Am I correct that this should be done before the moisture proofing is in place? Thank you
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No special moisture proofing is required for a FG shower insert. The insert is waterproof (or should be).
My thought was that the moisture proofing would protect the framing, insulation, and subfloor in the event of leakage from caulked areas around the perimeter as well as the shower head and controls. Your opinion? Thank you
All about how much you want to spend and what will help you sleep at night. Nothing wrong persay about doing it
The best defense against moisture problems in the floor or walls is to make sure they are designed with adequate drying capacity, and good air-sealing, so that any incidental moisture that does get in can not do any damage. That's really no different form any of the rest of the assemblies in your new build.
One of the walls will be an exterior wall. The wall assembly will consist of vinyl siding, Tyvek wrap, plywood, and Kraft faced FG batts. If we include some moisture proofing such as tile backboard or Wedi membrane, will this affect the ability of the wall to dry? If so, what is the solution?
That exterior wall is designed to dry to the outside. it should be fine.
As Akos said, the ability to dry needs to be combined with a good interior air-barrier. With those in place your walls are as safe as any of the others ones in the house.
This video from builder Josh Oduin might be useful to you:
Youtube is full of ideas.
The big issue with a lot of tub installs on outside walls is there is the lack of air barrier behind the tub itself. Besides making the shower liquid tight, this is the major issue that you need to fix if you want mold free bath.
Make sure the drywall in the tub area goes all the way to the floor, it is sealed with caulk against the top and bottom plate and the drywall is taped with a quality tape (ie 3m 8067) where it is notched for the lip of the tub to mount to the studs.