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Insulating a brick wall? I cut it open to find only 2″ of space between wood panel and brick…

jmraine | Posted in Energy Efficiency and Durability on

Question: I have a house built in the mid 60s . I just cut open the back split walls and found the lack of insulation in our brick exterior walls. There were days when the room was freezing so I want to add some insulation without hurting the bricks. Currently the layers from out to in are bricks — building felt- 1″ furring – 5 ply paper-wood “stuff”- 1″ furring. The furrings are 18″ apart. Should I remove the everything to the bare brick, redo furrings and use the 2″ foam insulation for R-10 or do I have to leave space for air? Or can I just use our existing furrings and cut the 5-ply stuff out? Thanks for your help.

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  1. GBA Editor
    Martin Holladay | | #1

    Does this house have any wood framing? Or do you have a structural brick wall that is holding up the roof?

    If your house has multi-wythe (thick) structural brick walls, you may want to read this article: Insulating Old Brick Buildings.

  2. jmraine | | #2

    Thanks and I have read the article over and over. It is multi-wythe so I know I can't go gang busters with the insulation and can't use fibre but I was looking to figure out what I can use. The build used cardboard. I have cut most of that out. I am just trying to insulate it now with an update. It all started because it was nasty old wood paneling and I wanted to put up drywall. So what should I use? The depth I have now is 2" because it has exterior wall then 3/4" furring. Then the gap where the paper was 1/2" and then another furring (3/4") that the wood panelling was hanging on. Thanks for the response. I have read the article carefully but e situations notated there are only a portion of what I am dealing with. Currently, the plan is an R-7.5 (1 1/2") depth foam with space for air travel.

  3. jmraine | | #3

    Side note: upper floor is wood with vinyl siding. So it's wood on top of brick multi-wythe.

  4. GBA Editor
    Martin Holladay | | #4

    The best approach would be to install 1.5 to 2 inches of closed-cell spray polyurethane foam. If your bricks are in good shape and are protected from large amounts of rain, then you should be OK.

    If you don't want to use spray foam, you could insulate with 2 inches of rigid foam. But you would have to make sure that you do a careful job of air sealing at the perimeter of each piece of foam, and between the foam and the bricks, so that there is no chance of air movement between the foam and the bricks.

  5. Expert Member
    Dana Dorsett | | #5

    +1 on the 1.5-2" of closed cell polyurethane applied directly to the brick.

    Any interior framing cavities could then be filled with either damp sprayed cellulose, damp sprayed JM Spider (fiberglass) @ 1.8lbs density, or rock wool batts.

    A greener alternative to a generic closed cell polyurethane would 2" of Icynene's 2lb density semi-open-cell water blown foam MD-R-200. It is somewhat more vapor permeable (1.3 perms @ 3") than standard grades of closed cell polyurethane (0.80-1.2 perms @ 1"), and has about the same ~R5/inch of rigid XPS, but since it''s blown with water rather than high global warming potential HFCs, it has but a tiny global warming footprint. The stuff they use for standard closed cell or XPS have global warming potentials more than 1000x CO2. Water's GWP is stubstantially less than 1x CO2. At 2" you'd be at about 2 perms with the 2lb semi-open Icynene, which is more vapor-tight than most latex paints, slightly tighter than a single layer of #15 felt, and tight enough that the moisture stored in the brick would not pose a threat to the framing or interior gypsum. It's as air tight as any 2lb foam. If there's room for and unbroken 3" (no studs or framing penetrating it) go for 3", and it would meet or beat 2x6 studwall performance.

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