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Existing 2×4 brick veneer wall with no weeps – what type of insulation in 2×4 cavity?

Peabody2 | Posted in Energy Efficiency and Durability on

Remodeling a 1960’s raised ranch near Chicago (5A).  The basement knee walls are approximately 4′ high brick veneer with 1″ air space full of mortar droppings and no weep holes then 1/2″ asphalt fiberboard sheathing on 2×4 framing.  The previous owner installed fiberglass insulation with Kraft facing and drywall.  When I ripped out the insulation I found piles of fiber on the sill plate.  The lower part of the sheathing seemed to be decomposing a bit, I’m guessing from the vapor being driven inward.  

Do you suggest fiberglass insulation in the 2×4 cavities with no kraft facing to allow  indoor drying?   A mason didn’t think drilling weep holes would help much with ventilation due to the droppings.   

Thank you in advance for your thoughts…

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Replies

  1. Expert Member
    Peter Yost | | #1

    Hi Peabody (if this is not your name, I apologize but always good to have a name to use in the GBA community) -

    This sure has the makings to be solar-driven moisture (see this article by Martin Holladay: https://www.greenbuildingadvisor.com/article/when-sunshine-drives-moisture-into-walls).

    You certainly would like to avoid what happened in the lead photo.

    If you have the FOUR required elements for solar-driven moisture as listed in Martin's article

    1. a reservoir cladding - you do--the brick veneer
    2. permeable wall sheathing - you do--the exterior fiberboard sheathing
    3. a polyethylene interior vapor retarder - you don't, at least not yet and the fact that previously the interior vapor retarder was the kraft paper facing on the batt may be why your wall is in a lot less trouble than it could have been
    4. central forced air conditioning

    I don't know what your "appetite" is for taking this wall apart--how many layers you are willing to demo--but here is my cut:

    If your brick veneer gets wet a lot--particularly getting wet followed by intense sunshine, you might want to consider redoing your exterior cladding. I know this is a huge job BUT the fact that you have mortar droppings acting as a capillary bridge between the cladding and the vapor permeable sheathing is a big problem. In fact, with the cladding removed you can deal with the compromised exterior sheathing.

    I would spend more time assessing just how wet your walls are getting and how much degradation there is to the fiberboard sheathing.

    Best - Peter

  2. Peabody2 | | #2

    Thanks for your response and link to the interesting article, Peter. I've been researching issues with reservoir-claddings and it doesn't seem like there is a simple retrofit solution. Despite it's flaws, this 4' brick veneer wall has held up fairly well the last 50 years. I don't want my "improvements" to cause more degradation. There are a few stud bays on the west wall where the bottom ~1" inch of the fiberboard shows signs of being wet at some time. Two window openings were cut into the brick veneer on the south side wall and the asphalt fiberboard sheathing was in good shape. During this project, I did see building paper felt applied to the asphalt fiberboard sheathing.

    It's basically a daylight basement, 4' below grade concrete wall and 4' above grade brick veneer wall. The previous owner installed furring with paneling over the bare concrete walls and fiberglass batts with Kraft facing in the 2x4 bays behind the brick veneer. My plan is to cover the concrete with 2" rigid insulation, furring, gyp board, and install unfaced fiberglass insulation in the 2x4 bays behind the brick veneer/asphalt fiberboard sheathing. I had considered cut and cobbling rigid insulation into these stud bays but I'm concerned this might slow the drying of the asphalt fiberboard sheathing to the interior.

    Your suggestion of removing the brick veneer would be ideal, but just not possible for me from a $$ perspective. Do you think unfaced or faced fiberglass batts would be better for this wall assembly? Or something else?

    Thank you again for your time!
    Amy (my name was taken, Peabody is a nickname)

  3. Peabody2 | | #3

    Hello Peter,
    Looking at this study, https://www.appliedbuildingtech.com/system/files/modules/node/89/151207watervaporcontrolwithcifinal.pptx
    It seems like a class III interior vapor retarder (batt insulation - no kraft paper / gyp / latex paint) would be most appropriate for my existing wall assembly. Do you agree?
    Thanks in advance for your consideration.

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