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Community and Q&A

PolyIso inside 1949 brick veneer walls?

66Giovani | Posted in Energy Efficiency and Durability on

This 1949 Cape Cod style home is in SW lower Michigan just a short distance south of the zone 5A-6A line. My goal is to reach toward the 6A standards, esp. with the long, very sustained cold we had last winter.

The walls are very porous: brick veneer (but for upstairs, clapboard dormer), Insulite Bildrite Sheathing, and what appears to be mineral wool insulation in the wall cavities. The interior walls are covered with a smaller (2′ x 4′ ish–judging by the seams that are showing) type of gypsum panel that was apparently used at that time.

This is a modestly sized house

I have not broken into the walls to see how the wall cavity looks as far as condensation/moisture impact, but after being in the house for our first winter, I know the walls get VERY cold, and I see water marks on the bottom face of floor planks at the rim joist from the basement. There are plenty of gaps and passages for air: open mortar seams in the exterior veneer wall from house settling, gaps in the floor deck planking that extend to the perimeter, etc.

My thought is to place polyiso in the walls (where brick veneer present) with foil facing the exterior with 1/2″ air gap between the polyiso and Insulite sheathing–for 2 reasons: 1) stop airflow through the Insulite, and 2) stop heat from sun cooked brick walls from pushing heat and moisture into the walls from the outside. This would be a “cut-and-cobble” polyiso install (unless you have other suggestions for a reflective barrier) to get that layer (3/4″ or 1″) of polyiso inside the wall cavity, followed by closed cell spray foam (professionally installed) to complete the stud cavity, then 1″ polyiso over the interior studs to stop thermal bridging, and new gypsum panel.

If I’m not mistaken, Zone 5a called for a minimum of 1 1/2″ of polyiso in the wall cavity to prevent condensation from exterior – interior transfer, which, to me, meant it made sense to just continue with closed cell foam (either as board or spray foam) to fill the 3 1/2″ stud cavity and achieve a desired R with the whole assembly.

Suggestions on running electrical would be appreciated. I read a Q-A where it was stated that running wires under the baseboard is an option–and I assume a code-worthy option.? Rooms are not large, so I was not planning on a gap between the interior polyiso and the gypsum board.

This is a modestly sized home, with work to be done first on approx. 60′ of wall covering primarily south-facing bed/bath rooms on the main floor.

1- Is that a smart system? If not, what’s wrong?
2- Is the 1/2″ air gap between polyiso and exterior sheathing needed? I realize air gap is needed for the foil facing to really serve its intended purpose, but I wonder if the openness of the Insulite fiber changed factors in any way that could allow the foil facing to be directly next to the Insulite–air gap being less r-value than the polyiso.?
3- Is there any reason to NOT employ this same method to the North side of the house?–which only receives direct sun during a short period during high summer for maybe 2 hours before sunset. We still need to stop cold air through that Insulite fiberboard!
4- Am I missing anything?

Your expertise if greatly appreciated.
Thank you.

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  1. GBA Editor
    Martin Holladay | | #1

    Buildrite sheathing, as you may know, is fiberboard sheathing. It is vapor-permeable.

    If your brick veneer wall is built properly, there should be an air gap on the interior side of the brick veneer, followed by some type of weather barrier -- perhaps asphalt felt -- followed by wall sheathing (in your case, fiberboard sheathing).

    If the builders forgot to install asphalt felt, that would be unfortunate.

    Your brick veneer wall should also have weep holes at the bottom of the wall. Hopefully, the builders installed flashing at the base of the wall to direct water to the weep holes.

    The normal course of events is to finish all of your electrical wiring work before you insulate.

    Insulating your stud cavities with closed-cell spray foam is a good idea. The closed-cell spray foam will address inward solar vapor drive. There is no need to install any cut-and-cobble polyiso before spraying closed-cell spray foam on the interior side of the fiberboard sheathing.

    The only caveat I would make is that if you encounter any signs of water damage, proceed with caution. Figure out how the water is entering your wall assembly and correct the problem before proceeding.

  2. 66Giovani | | #2

    Thanks for the reply, Martin.

    RE: Shoulds? If only...
    RE: Weep holes? None. ...and there is no flashing visible at the base of the wall. From what I have read, this is all too common in homes of this vintage; and it can be unproductive to try and add weep holes without knowing that there is a good gap behind the brick to actually allow drainage. I'm open to suggestions, though.

    There are holes that were drilled in the brick exterior, apparently for termite extermination, and they were hastily filled with mortar caulk. Due to some foundation cracking and brick veneer/mortar cracking, we are going to have an engineer assess the structure.

    RE: felt over the exterior sheathing? Golly, Ned; I hope so. I just don't know. I will try to find a hole in the brick that isn't filled-in too well and attempt to get some light and my eyeball in there to look for felt.

    So any benefit of a foil face to reduce heat gain inside the wall is not worth the hassle/effort/time/etc? Did I read between your lines correctly? I figured it would make the whole assembly much less prone to year-round solar heat gain as well as stop vapor, more so than closed-cell foam alone.

    PS.: How much time on any given day do you allocate to advising blooming green advocates through this Q-A forum?

    Your counsel is appreciated.

  3. GBA Editor
    Martin Holladay | | #3

    Q. "So any benefit of a foil face to reduce heat gain inside the wall is not worth the hassle/effort/time/etc? Did I read between your lines correctly? I figured it would make the whole assembly much less prone to year-round solar heat gain as well as stop vapor, more so than closed-cell foam alone."

    A. Closed-cell spray polyurethane foam provides an insulation layer with a high R-value per inch -- so it "reduces heat gain inside the wall" (and more importantly, inside your living room and bedroom). The spray foam is also a vapor barrier, so it stops inward solar vapor drive. Because it performs both of these functions, there is no need for any cut-and-cobble polyiso.

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