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Roxul and cladding help

Josh7447 | Posted in Green Building Techniques on

I need some help. I’m trying to build a house with 2×6 construction, zip sheathing with fast flash, 2″ of roxul comfortboard, 2×4 furring strips and lp smartside. I planned on using heco fasteners. First of all, is this an efficient wall assembly? I’m here in MO and there are no builders familiar with exterior insulation. I’m getting frustrated as everyone is trying to talk me out of using it. Tilt up construction is common here so has anybody successfully done this in a tilt up fashion or should I have the framers do the sheathing and try to find another trade for roxul and cladding? Videos of this would be appreciated. I’ve watched many videos online but none with this sequence.

Would I be better off using a different cladding, say stucco to eliminate the furring strips and window bucks?

Finally, does anybody have a good suggestion for window buck besides plywood? I’ve seen therma buck but don’t want something soaked in chemicals. Alpen can factory attach 3.25″ extensions but for this setup I think I would need at least 4.25″.

Your help is always appreciated. Thanks josh

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  1. GBA Editor
    Martin Holladay | | #1

    Clearly, you need to locate a contractor who is willing to build your house according to the specifications you've chosen. Installing a continuous layer of exterior mineral wool, followed by furring strips, is still a fairly unusual (even exotic) way to build a wall, so it wouldn't surprise me to learn that you can't find anyone to be a guinea pig for your project.

    You need to find a builder you feel comfortable with who is either a GBA reader or willing to read the same articles that inspired you. That might help.

    If that's impossible, you'll need to negotiate these details until you and your builder come up with details that you are both comfortable with. You may have to let go of the dream of exterior mineral wool.

  2. JC72 | | #2

    IIRC Per Roxul you still need some sort of backer board for stucco when using mineral wool.

    Q: Have you considered ZIP-R w/ 1x4 furring strips?

    Btw...With siding the air gap created by using 2x4 furring is excessive. Using 1x4's will make window detailing much easier as well. Tbh you really don't even need the 1 inch gap provided by the 1x4's.

    My two cents.

  3. Josh7447 | | #3

    Thanks John. I would love the zip-r if I could get it with mineral wool. Im not a fan of the termiticides they have to put in the foam though. I'm checking with LP on the 1x4. I was told by someone on this board that would void the warranty but it doesn't sound like that's the case according to LP. I do appreciate the suggestions. It does sound like Alpen can get to 4.25" on the frames so just waiting to hear on cost.

  4. jberks | | #4

    My 2 cent's: after air sealing the zip sheathing seams, adding sheats of roxul comfortboard and screwing down 1x4 (or I prefer 4" ripped 3/4" ply) before your tiltup will save you tonnes of time in anguish trying to do it vertically off scaffold later.

    However, you will probably hear your framer complain till the cows come home (I'm trying to find a family friendly way of saying it)

    My current build, I had to tape the seams for the framer before he layed down tyvek on the sheathing... Because even though I was paying him to do it, he refused... Basically I payed him to watch ME do it. If I was any smart, I would have told him to lay the wall out and go home and I would have taped, tyveked, roxuled, and furred the wall myself and they could tilt it the next morning.

    To build green you pretty much gotta build it yourself or find an exceptional builder who actually cares about their work.

  5. Josh7447 | | #5

    I agree with you Jamie. Personally I don't see why it wouldn't be easy for the framers to do this on the ground. It probably wouldn't take very much longer to lay out the roxul, screw in the furring strips and attach the siding on the ground. Then stand the wall up.

  6. Expert Member

    It makes a lot of sense to do as much as you can on the deck before lifting the walls. In most areas, the problem is asking the framers to do it. Some small crews may do a variety of tasks, but typically framers frame and someone else does that. Its a bit like asking the drywallers to paint and trim out the interior.

  7. JC72 | | #7


    The foam used in ZIP-R isn't treated for termites. Where did you get that information?


  8. Josh7447 | | #8


    My apologies. You are correct as I was confusing that with another product. However I still don't like foam. Thanks

  9. brendanalbano | | #9

    Even if you're not doing a Passive House project, the PHIUS certified builder list might be a good place to look for a contractor who should be comfortable with exterior insulation. Looks like there are 3 in MO:

    Are any of them near you?

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