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Corrugated metal over mineral wool

user-6683358 | Posted in Green Building Techniques on

Hi, I am looking for ideas for installing vertical corrugated metal over Roxul comfort board.

A bit more about the project:
Zone 5B,
2×6 @ 24″ OC walls insulated with Roxul batts (R-23),
plywood, wrb, and
2″ Roxul Comfortboard (R-8), corrugated metal siding running vertically.

Do I need to install vertical furring a layer of horizontal furring to attach the corrugated panels to? Can the metal be attached directly over the comfortboard?

Thanks for any thoughts/ ideas.

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  1. GBA Editor
    Martin Holladay | | #1

    User-66 etc.,
    First of all, can you tell us your name?

    If the corrugated metal panels are sold as siding, your first responsibility is to install the siding as instructed by the siding manufacturer. Most siding manufacturers post their installation instructions online. If the instructions are unclear, you can contact the siding manufacturer by phone or email.

    One problem with trying to fasten siding through 2 inches of mineral wool is the need for very long fasteners. My instinct tells me that using furring strips will make the installation easier.

  2. Expert Member


    I don't think you could install it directly. You will certainly need some backing for flashing at the top, base, corners and at openings. Also, as the panels rely on gasketted fasteners, I don't think you could rely on them staying tight under a backing as soft as mineral wool.

    Corrugated panels have a lot of inherent rigidity, so you will only need horizontal furring at very infrequent intervals - say 4'-0"oc.

  3. user-6683358 | | #3

    Thanks for the replies Martin and Malcolm. My name is Stacey. (I updated my screen name after I made this post, but it didn't update to my chosen name "stacey v").

    Anyways, it was my hunch too that furring would be needed and the point about the gasketed fasteners is a good one. Would horizontal furring only still provide the drainage needed for a vented rain screen? (As you suggested Malcolm). This is my first project using exterior Roxul board, and I understand that it is softer and compresses more than rigid foam, but also that it is more breathable and drains.

    Attachment details from the manufacturer are all for attaching to a solid substrate, so furring it will be. The question do I need to install vertical furring first then horizontal to maintain drainage, or can I just do horizontal only when using Roxul exterior insulation.

    Thanks again for the feedback!

  4. user-6683358 | | #4

    PS - How do I get my user name updated? Here is a screen shot of my account profile.

  5. billingsdave | | #5

    I'm planning on a similar system for my cabin, with some variation. I'm going to put up 2" of Comfortboard against the WRB house wrap, then lag horizontal 2x4s on 24" centers to support my metal siding with 1 1/2" Comfortboard between the 2x4s. While the Comfortboard will compress more than rigid foam, it shouldn't be a problem as long as you don't over torque the lag bolts and keep the 2x4s (or furring strips) level with one another. Corrugated metal will provide plenty of air movement behind the siding to allow moisture to escape.

    If you haven't looked this Roxul brochure over, it's worth a look. Plenty of diagrams and instructions for different configurations and applications:

  6. user-6683358 | | #6

    Thanks David! That guide is very helpful.

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