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Is tile acceptable on a bathroom exterior wall with foam?

drewintoledo | Posted in General Questions on

I’d like to build using the REMOTE method. However, I see articles stating that walls with exterior foam board must dry to the inside. I’m interpreting this to mean that the interior of the walls must be permeable.
My bathrooms both contain an exterior wall. I’d like to build a fully tiled bathroom but I don’t know if it’s a good idea to tile the exterior wall. I believe that tile is not very permeable so the wall couldn’t dry to the inside.
Does anyone have an answer to this dilemma?

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  1. charlie_sullivan | | #1

    I would not worry about it unless you have a huge bathroom with a 20 foot exterior wall. There will be other drying paths for any moisture behind that wall. If you want to be extra sure to allow drying paths, you could drill some holes in the studs to allow lateral air movement around the tile.

  2. user-2310254 | | #2

    You can reduce your risk by using a good waterproofing system in the baths. Schluter would allow you to treat the entire space as a wet area.

  3. Expert Member

    Interior finishes are the achilles heel of wall systems designed to dry to the inside. Paints, wall paper, mirrors, and tile all impede the vapour path.

    I can't quite buy the argument that it somehow doesn't matter because it is just one wall. Surely it either is a problem or isn't. Having a wall that can't dry in a high moisture room would seem to be asking for trouble.

    That said I wonder if any remote homes have experienced problems with impermeable interiors, or if it is a purely theoretical concern?

    For peace of mind I would strap the wall horizontally with 2"x2"s leaving the ends open to the interior walls to provide a path for moisture to escape.

  4. user-2310254 | | #4

    Drew. You also might want to contact the Cold Climate Research Center ( It seems likely you could speak with someone who has real-world experience with REMOTE and this particular concern.

  5. GBA Editor
    Martin Holladay | | #5

    I'm more inclined to agree with Charlie than with Malcolm.

    With exterior foam and (I hope) a rainscreen gap, there won't be any moisture driven into the wall from the exterior. A rainscreen gap makes rain intrusion unlikely.

    The tile and the waterproofing layer behind the tile make it unlikely than indoor moisture is driven outward.

    Of course, you want to make sure that the wood components of the wall (studs and sheathing) are dry on the day that the insulation between the studs (if any) is installed, and remain dry until the tile work is performed. If everything starts out dry, everything should stay dry. A limited amount of drying can occur sideways, by diffusion. (Most REMOTE walls either have no insulation between the studs, or have air-permeable insulation like fiberglass batts between the studs.)

    Of course, if you want to install horizontal furring strips on the interior side of your studs, to encourage sideways drying, you can. Just make sure that you have an air barrier -- the air barrier can be vapor-permeable -- between the studs and the horizontal furring strips.

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