Shower enclosure exterior brick wall
I have a 123 year old structural brick house in Richmond, Va. climate zone 4. All the exterior walls are exposed to the elements save a 30 foot shared section with adjacent property. Only the front of the house is the higher quality glazed brick used for the fronts of old homes. All the other walls are your typical 1900s clay brick. Definitely need to repoint some areas. Am aware brick is porous etc and it’s obvious plenty of moisture travels through these walls as most of the plaster was cracking and falling , made even worse by drywall someone hung over top of the plaster. We’ve exposed all the brick from the inside. All of the inside walls have been sprayed with prosoco dust proofer , which from what I’ve read, is one of the only safe products to use as it allows the brick to continue to breathe. Problem I have is I need to build two shower enclosures in the 2 bathrooms. I would frame the enclosures 1 inch off the brick by tying into the ceiling and floor joists. Plan to use Kerdi board for the tile. Bathroom will have fan on humidistat. Do I need to worry about the wood framing or the kerdi board having mold and moisture issues from the moisture that will inevitably come through the brick if I have this 1 inch air gap ? Am not insulating anything as I’ve read it’s just too dicey. The building does have central air and heat via ducts in crawl and attic.
thank you!
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I have a lot of experience with houses of this type and vintage, DC has tens of thousands of them, I've lived in several.
First, if your plaster is failing it means liquid water is penetrating, this is not normal or acceptable. Yes, the soft brick is somewhat porous, but it shouldn't allow liquid water through. You need to check your pointing and flashing around windows and doors. Also check that gutters and downspouts aren't allowing water to hit the wall directly or splash onto it.
Walls like this are insulated all the time with no issues.
That said, the brick needs to be able to dry when it gets wet. The general rule is that moisture moves from warm to cool and you want any assembly to be able to dry to the cool side. According to the design temperature guide (https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf ) Richmond has a heating-degree-day to cooling-degree-day ration of exactly 1.0, so there isn't really a dominant hot or cold side to the wall. But you want it to dry to the exterior. So having a vapor barrier on the inside is not a problem.
In DC it's not uncommon for houses of that vintage to have a layer of roofing tar between the brick and the plaster.