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Community and Q&A

Insulating interior wall over brick in Phoenix

Shawnus | Posted in Energy Efficiency and Durability on

I have a home in Phoenix built in 1958. All exterior walls are brick and there is exposed brick for interior wall surfaces of those walls.

This is fine, except in one bedroom which gets alot of sun on its two brick walls (the other two walls are interior and are stud/drywall). In summer this bedroom is 5-10° hotter than the rest of the house, and the walls are warm to the touch. I’ve even tried putting a special vent fan faceplate to move more cold air in there- it only helped slightly.

I’m considering insulating the interior of the two brick walls in this room. Two questions:

1. Will this work without deteriorating the brick?

2. How should I do it? 1″ furring strips and insulation, then drywall? Do I leave any space between the insulation and the brick or do I cut it to fit snug between the furring strips?

Thanks in advance.

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  1. Expert Member
    Dana Dorsett | | #1

    If the brick is in pretty good shape, insulating on the interior isn't very risky in a Phoenix US zone 2B climate.

    A layer of 1" foil-faced polyisocyanurate foam with seams taped would meet current code-min for brick wall in Zone 2B. See the "mass wall" prescriptives for zone 2:

    If you use 1x furring through-screwed to the brick on which to hang the wallboard you will be giving up only 2.25" of room dimension.

    With a 2x4 / R13 wall you'd be giving up 4" of space, and you would have potential moisture issues behind the finish paint in an air conditioned house when the sun bakes out the moisture after a rain event. If that's the route you take it's worth putting 1/4" fan-fold XPS between the brick and the studs/insulation as a vapor retarder, which gives you a ~10% improvement in thermal performance as well.

  2. Shawnus | | #2


  3. jackofalltrades777 | | #3

    One thing to remember is that with Phoenix it is not IF you get termites, it is WHEN you get termites. I would put down termiticide treatment before you put up the wood walls. Termites can find their way through gaps and cavities in the exterior walls and slab.

    The old CMU homes in Phoenix have that problem since the CMU's were hollow and allowed for termites to tunnel through and get into interior wood walls and the wood roof trusses in the attic. The way you find out you have the termites is that one day you will see a termite tube hanging from your ceiling.

  4. GBA Editor
    Martin Holladay | | #4

    One problem with installing rigid foam against an old brick wall is that air can leak into the gap between the bumpy brick surface and the foam. In your climate zone, this won't be a big problem -- but it still makes sense to seal the perimeter of each sheet of rigid foam insulation with caulk or canned spray foam. (The sealant should be installed between the bricks and the rigid foam.)

    A superior way to insulate this type of wall is with closed-cell spray polyurethane foam. There are two downsides -- this type of spray foam has an environmentally damaging blowing agent, and the foam is expensive -- but from a performance standpoint, closed-cell spray foam is unbeatable.

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