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open cell spray foam before exterior polyiso and brick

darko9000 | Posted in General Questions on
Hello everybody,
I’m looking to get some advice on a question that I’m not sure how to proceed,
My wife and I are living in North Carolina and currently building our forever home. I have passed all the roughing inspections and I’m ready to install interior open cell spray foam insulation in the wall cavity.
My wall structure consists of exterior brick, one inch air gap, 2-inch polyiso, half inch zip sheeting, then 2 x 6 interior framing with a spray foam. This is a mostly DIY project. I have meticulously gone over all of the exterior zip sheeting and used liquid flashing to seal any seem any nail head and any opening. All the windows are installed, and the roof is shingled so basically the house is dried in. My blower door score was 1.5 so I was super happy about that because that was a lot of work to get done
 I have a spray foam contractor set to come out and spray foam the interior walls but now I’m having second thoughts about doing that, before the exterior insulation and brick are installed.
When it rains, I don’t get any water infiltration anywhere in the house. The little bit of water that splashes on the zip sheeting plywood is down by the foundation, but no water gets in. Should I wait to have spray foam done after I have a brick on the house or I’m being too paranoid? It’s so hard these days to get the contractors to show up, or line up with when you need them, so I’m having concern putting off doing spray farm until I’m done with the brick or should i not do spray foam until brick is on the house?
I’m also thinking the polyiso is going to get wet if it rains while being installed on the exterior but I’m assuming once that polyiso on the exterior is covered with brick, it should eventually dry off and stay dry because of 1 inch air gap between the brick in polyiso.
I’m also thinking how do those builders who use rockwool insulation on the exterior do this? I’m assuming if it rains that stuff must be soaked with water until either a brick or siding is installed and then eventually it dries off without any issues, is my thinking correct here or am I missing something?
Is there anybody that has a little bit more knowledge about this they can share with me?
Darko in North Carolina


  1. Expert Member
    ARMANDO COBO | | #1

    The initial description of your wall assembly is good. Polyiso is a closed cell so it won’t be affected by rain, and if installed with approved tape, the polyiso becomes a WRB... Edit: I would use 2-1" layers of taped polyiso, with staggered seams vs. 1-2" taped layer.

    Installing ocSPF in the framing cavities is good, and should not be a problem if done before brick work, your wall assembly is good, but I would make a suggestion to install dense-packed cellulose instead of ocSPF, since cellulose is a hygroscopic insulation which could buffer interior moisture for a short time in your climate zone. (Just preference)

    The 1” air space between the polyiso and brick is good for proper drainage. I will make sure you install metal bug/ant/wasp/termite barriers/screens around all openings to stop nesting, including weep-hole and freeze board screens.

    Mineral wool has a very high vapor permeance, so it will dry quickly if it gets wet. Mineral wool is also a great choice for exterior insulation, especially on fire-prone areas, but is has half of the R-value of the polyiso. (Trade-offs)

    1. darko9000 | | #2

      Hi Armando, thanks for your reply.

      that makes me feel better, for a minute there I thought maybe I should not be doing that.

      I took a drive to a couple of job sites this morning and I saw one house getting spray foam with only having the wrap on the exterior sheeting so I thought if the builder is doing this, I should be ok.

      When I was originally planning this, I was thinking about doing cellulose insulation. I 've had a very hard time finding contractors who even do this in my area, comparing to spray foam contractors which I had 5 bids within a few days. I was even considering doing a dense pack cellulose myself I spend a couple of weeks doing research and watching videos of how this is done but ultimately gave up considering the material price renting the machine and my time, it didn't seem like I am saving a lot comparing to spray foam. I'm already doing quite a bit of other work myself including plumbing electrical and mechanical, So it just seemed too much work on top of all this stuff what I'm doing.


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