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Brick Ledge help with Rigid Foam Over CMU

Wayne321 | Posted in General Questions on

Hello,

I am doing a custom new construction home and am trying to get some economical ideas on how to best provide a brick ledge when I add up to 4″ of exterior rigid foam in zone 5.

Currently, the plan is to have a 10 inch CMU basement, that then steps down to 6 inch CMU for 2×6 stud walls, the other 4 inches is to be used for brick that starts just below grade. The brick travels through the first floor. The second floor will be vinyl double lap siding.

I wish to add a layer of external rigid foam up to 4 inches thick that will be placed from the footer up. The CMU will also have a water proofing compound applied.

So until the brick ledge is created, it would be CMU – water proofing compound – rigid foam board up to 4″. At the brick ledge it would be 2×6 stud – 7/16 sheathing – rigid foam board – brick.

Second floor will be 2×6 stud- 7/16 sheathing – rigid foam board – 1×2 furring strips or wider – vinyl siding

Ideally I would love to lose the brick altogether, but the township I’m building in has it as a requirement. I was thinking to maybe have 10 inch block until the row where the brick is to start and use a 14 inch block there to hold the brick. I’ve also been trying to find Corbel CMU that would fit here.

Any thoughts are greatly appreciated. Thank you.

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    Would the township accept thin-brick siding system, or does it absolutely have to be full-thickness brick resting on the foundation?

    There are multiple vendors of this type of product, where ~1" thick bricks get set into a steel support system that is fastened to a framed wall (or furring over foam through screwed to the framed wall), with pointing mortar applied. To give the appearance of full-brick the corner brick-lets have lap around the corner with an L.

    https://brickit.com/systems

    https://exteriordesigns.com/thin-brick/

  2. Wayne321 | | #2

    Dana,

    Thank you for the idea. I will inquire with my builder / township if this would be adequate. The only other solutions I've found so far is to build with 12 inch (for 2 inch foam) or 14 inch (for 4 inch foam) block walls. Or build with the 10 inch block and add an additional 4 inch block to hold the brick.

    The builder had mentioned going to 12 inch block over 10 inch would roughly be $1500 in material and I'll need to see what it is for 14 inch, but it may be a similar step of $1500. I might do the 12 inch block with 2 inches of exterior foam. I worry that being in zone 5, 2 inches of exterior EPS with 2x6 walls filled with either spray cellulose or fiberglass batt may not be enough.

  3. user-2310254 | | #3

    Wayne,

    This article has some relevant information: https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing

    In Zone 5, it looks like 1.5 to 2 inches of polyiso would be sufficient. Two inches of EPS would be close to the minimum. It also might be worth considering a 2X4 wall.

  4. Expert Member
    Dana Dorsett | | #4

    It's far better to back off to 2x4 framing and keep the 4" of foam than to thin out the foam.

    2" of Type-II EPS is R8.4 @ 75F mean temp through the foam, but R9+ at outdoor temperatures that matter from a dew point control perspective. It's legitimate to use the ASTM C581 performance tested at 40F mean temp through the foam in zone 5 when all of the foam is on the exterior of the sheathing (sheathing that would average 40F or higher over the season.) Most EPS vendors specify both the labeled-R (which has to be at 75F, meant temp, per the FTC) as well as 40F. Many will specify it at 25F too, but the 25F would be cooler than you'd see in this stackup.

    See Table 3 in this document:

    http://specs.duro-last.com/download?id=451&type=pdf

    Their Type-II EPS is R4.55/inch @ 40F which would mean you're good for at least R9.1 at outdoor temperatures that matter. IRC chapter 7 calls out R7.5 minimum for 2 x 6 framed walls at a presumptive R20 cavity fill, which is where standard density fiberglass batts and 2.8-3.5lbs celluose would be. Even with R23 dense packed fiberglass or rock wool you'd still make it:

    R7.5 x R23/R20 = ~R8.6, and you'd have more than R9.

    The whole-wall R of a 2x6/R20 +2" EPS wall comes in at about R23-R24 after factoring in the thermal bridging of the framing and adding in the R-values of the sideing/sheathing/wallboard etc.

    At the same wall thickness a 2x4/R15 + 4" EPS stackup the whole-wall performance would be ~R27-R28, and it would have HUGE dew point margin.

  5. AlexPoi | | #5

    Here's a document providing several options and their efficiency in case thin veneer is not an option :
    https://rdh.com/wp-content/uploads/2014/04/Masonry_Veneer_Support_Details___FINAL.pdf

  6. Wayne321 | | #6

    Thanks everyone. Definitely have given me some ideas that I need to discuss with my builder.

    I'll see what it cost to go the 14 inch block over the 12 inch block while also asking about the thin brick. Then I'll decide to keep 2x6 with 12 or 14 inch block or go to 2x4 with 10 or 12 inch block. Would have 2 or 4 inches of EPS respectively.

  7. Wayne321 | | #7

    So right now I'm probably going with 12 inch concrete block, 2x6 wall, 2 inches of EPS type 2, and 4 inches of brick (for first floor) and vinyl lap siding (for rest of house).

    The wall will be either fiberglass unfaced batts or sprayed cellulose (my preference).

    Thank you all for the ideas!

  8. walta100 | | #8

    Think about getting poured concrete walls.

    From an energy point of view all the voids with convection loops circulating air in the wall are bad things. How will they air seal the CMU from the required weep space between the brick and foam?

    When your “water proofing” fails just the thought of CMU filled with water, makes my skin crawl. My guess is you will not get a life time guaranty against seepage.

    Walta

  9. Jon_R | | #9

    Block can also channel water down to the bottom blocks where it can leak out into the basement (personal experience here). Foam can be put into the forms with a poured concrete wall. I assume that a brick pattern in the poured concrete wouldn't fly.

    If external foam isn't practical (due to an extended brick ledge), internal foam is an option.

  10. Reid Baldwin | | #10

    The article at https://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/airport-house-walls-and-insulation, particularly Image 2, shows how I handled this in my house, which is also zone 5. I have a 9 1/4 inch thick poured concrete foundation with a 4 inch brick ledge. The floor structure did not go all the way to the edge in order to make room for 2 inches of foam. I used graphite infused EPS to get a little extra R-value for dewpoint control. Polyiso would provide a little more (subject to some dispute at low temperature). I considered metal angle brackets to extend the brick ledge so I could go with thicker foam, but decided against it.

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