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Exterior Rigid Foam & WRB

ktcstl | Posted in General Questions on


I am retrofitting a small house and going back and forth on the order of my 1.5″ EPS rigid foam & WRB/air tight layer (Solitex Mento 1000).

From the inside to the outside, I was planning on having the full assembly be:
5/8″ drywall
Intello Plus air barrier
Existing 2×4 stud wall w/ dense packed cellulose
Solitex Mento 1000 WRB/secondary air barrier
1.5″ EPS rigid foam board
3/4″ rain screen
horizontal lap siding

But should I switch the EPS and Solitex? I believe I’ve read that the order of those two won’t effect anything, and it’s a preference/detailing decision. Can someone help confirm that is true? Or correct me if I’m wrong?
Zone 4A.


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  1. onslow | | #1


    Read the comments on this thread as a start point-

    You can search the GBA site for similar.

    The Thermal Tight product from Thermal Buck might be a good choice for you. As others noted the window/door detailing is the critical weak point. I have middie windows and opted to skin the entire house with Henry BlueSkin which wraps out and around the window bucks. I do have an air gap between the Henry WRB and my EPS as a belt and suspenders guard against any water making it past the first air gap behind the stucco finish.

    1. ktcstl | | #3

      Thank you for the feedback Roger!

    2. Charlie_P_123 | | #5

      Thread Hijack segue, sorry!

      Roger, could you elaborate on the air gap you have between the Henry WRB and EPS? I have been considering this on our wall layout.

      Did you use a thin entangled mesh spacer material akin to Henry's drainage mat?

      Thanks very much, and sorry for the intrusion. I hope this is close enough to the OP topic

  2. creativedestruction | | #2


    Consider all the transitions of the WRB air barrier, and strive for continuity of air control and drainage. More often than not, the WRB/air barrier makes the most sense protected behind the foam insulation directly on the existing sheathing (if you have it) so it can interface with rough opening air and weather control layers. In that location, it's better protected from temperature extremes, moisture cycling and movement, likely giving the taped joints a longer life. EPS can handle the incidental moisture that gets through the siding without issue as long as the bottom is drained and protected from critters along with the rainscreen.

    1. ktcstl | | #4

      Thank you Jason! And oops - I left out the existing sheathing from my assembly list. There's definitely sheathing.

      I appreciate your response, and your reasoning makes complete sense to me. I'll go ahead with the WRB/air barrier directly over the sheathing, and then the foam outward of that.

      1. Expert Member
        MALCOLM TAYLOR | | #6


        Think through the detailing of your openings (doors, windows) before deciding where to place the WRB. If it's on the sheathing, it means running the flashing back to that plane.

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