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Community and Q&A

Vapor barrier

Beth Puyau | Posted in General Questions on

Hi. I live in Houston and unfortunately bought a house that has some issues with water penetration in several areas due to brick parapets extending above the roofline that were never capped. The biggest area of water entry is in the master bath which we have completely gutted down to the studs – several of which have to be replaced due to rot and deterioration over many years.

The capping and coping is underway, but my problem is this: Between the studs and the brick was attached the original vapor barrier from 1984, but it is also deteriorated to the point of needing to be replaced as well. How in the world do you replace the vapor barrier between the studs and the brick, and do you absolutely have to have that component?

The studs were secured to the brick at regular intervals….not sure how to reattach the new studs to the brick either. On the interior of the studs, there will be Hardie cement board followed by shower tile on three walls.

Any help would be appreciated…. Thanks!

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Replies

  1. D Dorsett | | #1

    Ideally you would have a "weather resistant barrier" (WRB) between the brick and the structural sheathing, that is at least semi-permeable to water vapor. Traditionally this would have been tar-paper type materials, or sometimes rosin-paper. I'm not sure what was in vogue in your area in 1984. What does it look like?

    Brick is usually anchored to structural framing with masonry ties- metal pieces that get screwed or nailed to the studs, with the other end embedded in the mortar.

    There is no replacing the vapor barrier unless you're re-building the brick. But as long as the house is structurally sound and all of the bulk-water issues have been adequately and carefully addressed, there isn't an urgent need to replace it. The layers to the interior need to be sufficiently vapor permeable that the structural sheathing and studs can dry toward the drier air-conditioned interior. Cement board and most tile is sufficiently vapor permeable, vinyl wall paper or fiberglass tub-surrounds not so much.

    In an absolute worst-case scenario, under some conditions you may be able to safely fill the cavity between the brick & sheathing with slow-rise closed cell polyurethane foam, which has some risk to it, and would be very difficult to remove if it needed to come out.

    How is the roof designed to drain?

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Beth,
    Dana's first point is important: you don't want an exterior vapor barrier at this location. I'm guessing that when you wrote "vapor barrier," you were talking about either asphalt felt (tar paper) or housewrap (something like Tyvek or Typar). These products aren't vapor barriers; they are vapor-permeable. For more information on this these products (called water-resistive barriers, or WRBs), see All About Water-Resistive Barriers.

    You face a difficult repair job. How to tackle the repairs depends on how extensive the rot is. If the studs are rotten, and the sheathing is gone -- I assume that the sheathing must be gone, or else you wouldn't have noticed that the WRB has deteriorated -- and the brick ties are hanging in thin air, because they are no longer attached to anything, you have a potential problem that is so significant that it may be necessary to remove all of the brick veneer on that side of the building, and start from scratch from the bottom of the wall.

    If the rotten area is 2 feet by 4 feet, I wouldn't worry too much. If the rotten area is 6 feet by 7 feet, however, or larger, I would call in a structural engineer and an experienced mason to come up with a plan.

    Here is the risk: In a wind storm, one side of the house (the windward side) is pressurized, while the opposite side of the house (the leeward side) is depressurized. If your brick veneer lacks adequate brick ties, the bricks on the leeward side can be sucked off the house during a wind storm. It happens.

  3. D Dorsett | | #3

    FWIW: In a Houston US climate zone 2 location if you were to have a true vapor barrier in the stackup, putting it on the exterior side, between the brick and the structural sheathing would be the best location, since the spring/summer/fall moisture drives from the outdoors are higher than the wintertime moisture drives from the interior.

    But true vapor barriers are always a bit of a two edges sword, since it eliminates all possibility of drying to one side or the other. In most building types in that climate fairly modest vapor retarders or "smart" vapor retarders would provide the highest moisture resilience. As with most moisture/rot problems, this one was clearly related to the bulk water moisture intrusion, not vapor diffusion.

  4. Beth Puyau | | #4

    Thanks for the help. Here is a pic of the worst damage. (Dangling stud and remnants of barrier).

  5. D Dorsett | | #5

    This looks like there is sheathing at all on the exterior side of the studs!!

    This changes things a bit. How much distance is there from the stud edge to the brick?

  6. Beth Puyau | | #6

    Mostly it is 2 and 1/4 inches, except where there is excessive grout. (from the stud edge to the brick)

  7. Beth Puyau | | #7

    D, you had asked earlier how water drained from the roof. Below is a pic which should give some idea. Thanks again for your input..... :-)

    .

  8. User avatar
    Dana Dorsett | | #8

    With 2" + of space between the brick & stud edges you have sufficient space to install something there- the question becomes how attach it and air seal it.

    You can probably install fan-fold 1/4" XPS siding underlayment (eg: http://www.homedepot.com/p/Owens-Corning-FOAMULAR-1-4-in-x-4-ft-x-50-ft-R-1-Fanfold-Insulation-Sheathing-10UM/100320301 ),glued to the stud edges with foam board construction adhesive inserting 2 x 2" blocks of EPS or something else as a compressive wedge to hold the XPS tight to the framing as the adhesive sets. Then go back over it sealing the seams with housewrap tape, and edges with can-foam before installing the cavity insulation. There are multiple vendors & types- don't use a perforated version or you won't be able to make it air-tight. Siding underlayments usually have a thin bonded facer bringing it's vapor permeance down to something between 0.8-2 perms, which is just about right, and it's possible to use fan-fold goods as the primary weather resistant barrier even under leakier siding than brick, provided it's taped correctly. Since you don't have structural sheathing it won't be quite the same as a weather resistant barrier application, but it's way better than nothing. Since it comes in 4' x 50' sheets you'll need 2 sheets per story. With 1/4" goods it's possible to lap it rather than butt-fit the sheets together. If lapped such that any moisture running down the surface drains to the cavity rather than getting scooped into the insulation it'll do pretty well, even if the tape/foam sealing on the seam isn't perfect.

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