Helpful? 0

Moisture management

I am a builder in a suburb south of Dallas, TX area. I have a homeowner that wants to install tile from floor to ceiling in the master shower (including the ceiling) that is on an exterior wall. How do we prevent blocking moisture inside the 2x6 wall?

Asked by Tracy Mitchell
Posted Tue, 05/13/2014 - 17:31


2 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Helpful? 0

Hopefully, your tile contractor is familiar with shower installations, and understands how to make a tile installation waterproof.

When a shower is located on an exterior wall, there are at least two potential moisture worries: vapor diffusion and bulk-water leaks. Some backerboards, including polystyrene backerboards and gypsum-core backerboards such as Dens-Shield and GreenGlass, are already vapor retarders. In these cases, no additional vapor retarder is necessary or recommended, even when it is installed on an exterior wall.

Other types of backerboard, including cement backerboard and fiber-cement backerboard, are vapor-permeable. The permeance of HardieBacker ranges from 1.75 perms to 2.84 perms, depending on thickness, making it fairly permeable to water vapor. Although manufacturers of cement backerboard have not had their
products tested for vapor permeance, it’s safe to say that cement backerboard is highly permeable.

Manufacturers of cement backerboard generally recommend that a moisture barrier of some sort (WonderBoard calls for #15 felt or 4-mil polyethylene sheeting) be installed behind the backerboard when used in a wet location. According to some tile contractors, however, this is bad advice. “Plastic is a bad idea because you are nailing it on and putting holes in it,” says Tom Meehan. “When there is plastic, I’ve found mold behind the plastic. It locks any moisture behind it, and the moisture can’t dry.” If you want to waterproof the wall, Meehan recommends the use of a liquid-applied membrane such as Laticrete Hydro Ban or Mapei Mapelastic AquaDefense on top of the backerboard. For a steam shower, he prefers a sheet membrane from Kerdi or Noble.

Ideally, this type of wall will be able to dry outward. If that isn't possible, at least make sure that flashing details are impeccable, so that wind-driven rain is prevented from entering the wall assembly.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 05/14/2014 - 04:40

Helpful? 0

Redgard also Martin.

As to Southern build, if you add rigid foam behind backer board that may help make the shower less able to collect outside moisture behind it from outside humid air condensing if that is what your question relates to.

Redgard.png Redgard 1.jpg
Answered by aj builder, Upstate NY Zone 6a
Posted Wed, 05/14/2014 - 07:02

Other Questions in Green building techniques

Air Sealing Question - Assistance Requested for 6th Side of Building Envelope

In Green building techniques | Asked by Howard Lederman | Sep 14, 14

I'm wondering if you can insulate the attic roof rafters

In General questions | Asked by kristin burton | Sep 12, 14

Liability insurance - what would that cover?

In General questions | Asked by George G | Sep 12, 14

Zone 4B - 2012 IBC and SHGC

In Building Code Questions | Asked by Peter L | Sep 13, 14

Inset 2x6 sill plate

In Green building techniques | Asked by Craig Harper | Sep 14, 14
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!