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We have about 13 inches of 3-wythe brick load-bearing walls

tenNmw58np | Posted in Energy Efficiency and Durability on

We are not doing any insulation on the brick walls, but are having issues with the building inspector coming up with a framing plan. We live in MN. We have fought the city and won a battle so that we do not have to insulate because of the fears of the failure of our brick because of the freeze thaw cycle here.

Our trouble now is framing issues with the inspector. Our plan is to use the existing furring strips that are attached to 3 inch wide embedded embers in the brick. Most are still in tact and very sturdy. Our plan is to attach the drywall to the furring strips, but the inspector is worried about the dewpoint and the drywall becoming wet because of condensation.

The only change that we are making is that we have removed the lath & plaster and are adding 1/2 drywall. Does anyone have any experience with this? The inspector has concerns about where the dew point is, and how it has changed now by removing the plaster….. If anyone has any advice or information I am all ears. We have been battling them for almost 3 months now and we just need some resolution.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Kristina,
    As long as the building is heated in winter, the drywall will be close to room temperature, and will therefore be warm and dry -- just as the plaster used to be.

  2. tenNmw58np | | #2

    Yes the building will be heated in the Winter. I thought that the temperature of the drywall, and the heat that would pass to the brick would be about the same as it was for the plaster.

  3. Expert Member
    Michael Maines | | #3

    Kristina, it might help your inspector understand what's going on in the wall if you draw a wall section to scale, something like the one below. On the exterior side, draw a horizontal line representing outdoor temperature. A few inches above that, draw a horizontal line on the interior side of the wall, representing 70Ā° or whatever you like. Draw a line through the wall connecting the horizontal lines. That's the approximate temperature gradient within the wall, and will clearly show that no matter what the exterior temperature, as long as the interior is heated your drywall will be warm.

  4. user-1120647 | | #4

    Kristina,

    I think your inspector has a point. The issue is not the temperature of the drywall, but the temperature of the interior surface of the brick wall and the ability of vapour and interior air to reach it and condense within the wall assembly. What are the air and vapour control layers? When you apply the drywall to the furring strips, will this create an air gap? The change you are proposing could result in a significant change in the vapour and thermal profile of the wall and present condensation risk.

    I wouldn't rule out the insulation option so quickly. If done properly in conjunction with exterior water control measures, you can add interior insulation without increasing freeze/thaw risk and create a more energy efficient home in the process. Dr. John Straube can explain it better than me - check out his paper on the subject -

    http://www.buildingscience.com/documents/digests/bsd-114-interior-insulation-retrofits-of-load-bearing-masonry-walls-in-cold-climates/

    Trevor

  5. tenNmw58np | | #5

    I have actually been in contact with the Building Science corp, and because of the type of brick and the evidence of freeze thaw cycles in our paraphets we will not be insulating the walls. I have had several engineers and an architect advise against the insulation for our walls. All of the exterior items on the home have been addressed. Yes there will be an air gap and yes our plan is to attach the drywall right to the furring strips. They are very secure and have withstood the last 120 years. We will not be adding a vapor barrier as this would cause condensation between it and the brick, and we need the brick to breathe. We are proposing some sort of a ventilation system to help control the moisture, but I just don't see how drywall would allow or add any more moisture than the lath & plaster did...as there was an sir gap with the lath & plaster too.

  6. GBA Editor
    Martin Holladay | | #6

    Trevor,
    You have it backwards.

    You wrote, "The change you are proposing could result in a significant change in the vapour and thermal profile of the wall and present condensation risk."

    In fact, if there is no insulation, the bricks will be warmer and dryer that if insulation were installed.

  7. user-1120647 | | #7

    Sorry to be unclear. My point was that by removing the stucco and replacing it with drywall, you will be changing the vapour and thermal profile of the wall. If there was an air gap previously, then the change in the thermal profile will be minimum, but the vapour permiability of drywall is approximately 5 times higher than stucco, changing the vapour profile significantly. The other issue to consider is the moisture tolerance of drywall compared to stucco. Condensation moisture touching the stucco in the old wall system would not cause damage, while it only takes a small amount of moisture to cause problems with drywall.

    You just want to make sure that you do a really good job of controlling air and vapour flow from the inside in this low R wall system.

  8. Expert Member
    Michael Maines | | #8

    The original plaster likely had many coats of relatively impermeable oil-based and/or lead paint. The new drywall (installed over existing furring strips, according to Kristina) will likely be covered with permeable latex paint.

  9. GBA Editor
    Martin Holladay | | #9

    Michael and Trevor,
    While you are right that the vapor permeance of the drywall may differ from that of the painted plaster, (1) it's an easy matter to apply a coat of vapor-retarder paint to the drywall, and (2) my original point -- that the drywall will stay warm and dry all winter as long as the building is heated -- remains true.

  10. tenNmw58np | | #10

    Thanks everyone. I appreciate your input.

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