Storm damage repair–shower wall issue (vapor barrier?)
elenan3
| Posted in General Questions on
I am in zone 2. I am working on repairing a storm-damaged house that was built in about 1914 and is not air sealed. It was added onto in 2000 and no sheathing was used by the person that built the addition. We have been adding plywood sheathing plus new insulation, siding and drain wrap (and replacing any damaged dry wall) to the walls that don’t have any exterior sheathing. We got to a wall section with a shower on the inside and discovered mold visible from the outside on the shower substrate (some sort of tile backer board or just plain drywall). We now need to redo the shower.
I read the following thread: https://www.greenbuildingadvisor.com/question/is-the-shower-wall-a-vapor-barrier . The responders say that the shower surround is a vapor barrier and mention being meticulous with air sealing. We have been doing our best to seal the exterior plywood we have added to the 2000 addition, but the top of the bathroom wall appears to open into the soffit and the floor (the shower is on the 2nd floor) opens to other areas of the house that aren’t air sealed at all. We will do our best to seal the bathroom wall from the soffit on the inside. I can’t redo everything though nor do I have access to redo everything. The shower has 2 walls that are located on exterior walls of the house. It also goes all the way to the ceiling and the ceiling has tile. From reading the thread, it sounds like it will be a vapor barrier once installed correctly which we aren’t supposed to have in our zone.
It sounds like my best bet might be to air seal the area where the shower is now and not go all the way up to the ceiling with the new shower so that it isn’t a complete vapor barrier on the section of wall that makes up the shower. My husband would prefer that the shower go all up the way up to the ceiling.
Questions:
1. Should I limit the height of the shower to keep from having a complete vapor barrier on those sections or is there a way to have it go up to the ceiling that won’t cause issues?
2. I’m open to using any materials needed to air seal the walls of the shower. Do you have any recommendations?
3. My husband likes the Schluter Sealed System, if you have experience with it or other systems you like that you think a layperson can handle, it would be great to hear about your experience. I’ve been looking for a contractor and most have a minimum they want you to spend-this is a very small shower.
Thanks for any assistance you can provide
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Is someone able to recommend a book or articles I can read to better educate myself on this topic? A lot of construction resources I find aren’t oriented towards hot-humid climates.
elenan3,
I've so far been reticent to respond for exactly that reason, but let me take a stab.
The vapour drive in hot / humid climates is to the interior, so you want your walls to be fairly vapour-closed on the outside, and vapour-open on the inside to allow them to dry. The problem at the shower is you end up with a cold side vapour-barrier. The warm/moist outside air makes its way though the wall until it hits the colder impermeable shower and condenses causing moisture damage. The complete reverse of the usual situation in the heating dominated climates most of us are familiar with.
I would suggest a layer of either foam-board or closed cell spray-foam against the backside of the shower walls to keep it warm enough to prevent this.
I'm really having a hard time trying to reply to you. This is a test post.
Hopefully this doesn't show up 50 times, but the system doesn't seem to be allowing me to reply.
Thanks for responding Malcolm. I find insulation and vapor barriers confusing. And now I have to figure out how to do a shower in the hot-humid south :-/
We have a vapor open wall assembly on the walls of the house we have been repairing:
Fiber cement plank siding | TamlynWrap Drainable Wrap | 15/32 3-ply CDX plywood | Rockwool Comfortbatt R15 insulation | Georgia Pacific - Toughrock Fiberguard X Mold-Guard Gypsum Board
We are trying to finish the outside house repairs before we get to much further into hurricane season. We sprayed the mold and closed the shower wall sections and will work on the shower when we finish the outside (hopefully this week). The shower wall sections have:
Fiber cement plank siding | TamlynWrap Drainable Wrap | 15/32 3-ply CDX plywood | tile substrate (looks like green rock) | tile
How would the foam-board or closed cell spray-foam work with the wall assembly we have been using in the repair or would we do something different on the shower walls?
I thought if we used Schluter, we would add the rockwool after the plywood and replace the tile substrate with Kerdi-board or drywall/Kerdi membrane then tile. Regardless of what we use we have to make sure the shower sections of the wall are air sealed as tightly as we can make them. Please bear with my ignorance on the subject.
elenan3,
The foam board or spray foam in each stud bay against the backside of the shower will keep the moist air that has come from the outside from condensing, or mold from growing. Your wall assembly would remain the same as elsewhere with the exception of that 1" of foam, which should be taped and sealed at the perimeter.
I want to make sure I'm understanding. For example if we use Kerdi-board, are you saying the wall assembly would be the following (listed outside to inside)?
Fiber cement plank siding | TamlynWrap Drainable Wrap | 15/32 3-ply CDX plywood | Rockwool Comfortbatt R15 insulation | Foam board or spray foam | Kerdi-board | tile
elenan3,
Yes, although if you use thick enough Kerdi-board it will act as the insulation and you could forgo the foam layer.
Thanks for the reply letting me know that the Kerdi-Board can act as the insulation. I have a few questions, but I'm just going to ask one more. How do I determine the appropriate thickness?
I've been reading about Kerdi and discovered today that foam core backer boards for showers don't appear to be approved in the building code adopted by the city (IRC 2021). I need to contact them to see if that is the case. It also looks like I might be able to get it approved as an alternate method, but the fee associated with the review may be cost prohibitive.
elenan,
An inch of any type of foam will work in zone 2.
For some reason, I'm getting a "Your reply needs moderation" on the reply I want to post. I had to create a new account last week because I couldn't get anything to post. Hopefully it will come through soon.