We are in California and doing a bathroom remodel that required removing all the materials down to the studs. If we use greenboard or hardyback, is there an additional requirement of a waterproof membrane for the small exterior wall? Is this an extra precaution or a requirement, and is that requirement dependent upon certain states or weather conditions (extreme temps, etc.)

nah, it only keeps the house from rotting away, if you don't care, you can skip it.

30-50 bucks one way, hundreds of thousands the other. it's a wash, right?

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best practices far as I can Google 'em is that exterior walls need a semiporous water shield on the outside (tarpaper, housewrap) and a hard water shield on the inside (8 mil poly). best practices around a shower is everything lets water to the studs except a rubber or 8 mil poly membrane over the studs, "redtaped" over nails and seams, then the tile backer (hardieboard, durock, cement board), and then the tile. if you are using Kerdi waterproofing, see the Schluter website for recommended installation. never ever use any drywall in a wet area under current law, regardless of what used to be allowed in the dark ages.

this is not localized, this is the uniform building code as far as this non-contractor can determine. code is minimum requirement. your local authorities may have stricter regulations, go down to city hall and ask.

and in california or other seismic zones, you might need additional reinforcement of any walls due to earthquake issues. because of your location, you will have to talk to the building inspectors to be sure you are not going to have to tear it all out for safety violations. any time you touch an area, it has to be redone to current building code. that gets harsher every year in California as the seismic research gets better.

This message has been edited. Last edited by: swschrad,

Personally, I think you should use a water proofing membrane, but if you're using glazed wall tiles set on a proper tile backer, then I'd be hard pressed to give a reason why the waterproofing membrane is all that important.

You see, the whole idea behind using a water proofing membrane is the acknowledgement that neither properly grouted ceramic tile nor cement board are impermeable to moisture. That is, moisture can migrate through porous ceramic tile and porous grout almost as easily as it can migrate through porous cement tile backer board. And the result of moisture migration through the tiling can be mold growth behind the tiling and possibly even wood rot.

But, on a bathroom or shower wall, you're using glazed ceramic tile, and that film of glass over the tile greatly diminishes the area through which moisture can migrate. Basically, if you're using glazed ceramic tile, the only way moisture can get into the wall is through the grout joints.

Now, if you also use a film forming acrylic sealer over your grout, then you're making it much harder for moisture to get into the grout in the first place.

Don't get me wrong, I believe people should use waterproofing membranes to do the best job they can, but it seems to me that where you most need that waterproof membrane is where you have porous floor tiles and unsealed grout, like you might on a tiled shower floor.

Also, I have 21 bathrooms in my building and not one of them has a waterproofing membrane between the tiling and the cement backer board, and none of them are showing any indication at all of deterioration of the tiling or that there's a problem that applying a waterproofing membrane would have prevented. But, they all have glazed ceramic wall tiles set in thin set over various kinds of tile backer boards, and all of the grout is sealed with an acrylic film forming sealer. So, I can't argue with my eyes are telling me.

However, this is in an apartment building where NONE of the bathroom walls are exterior walls, and that may make an important difference that I'm not aware of.

Also, on two occasions I've had to replace broken wall tiles, and in both cases the tiles were located where the shower spray would fall. And, in both cases, when I removed the old tile, the wall behind it looked perfectly normal. If there were moisture getting behind that tile, then there'd be trapped moisture and mildew growth. But the wall looked exactly the way I expected: dry as a bone.

This message has been edited. Last edited by: Nestor,