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Could anyone suggest a fastener that would work well for attaching 6 in. mineral wool to the exterior of sheathing and studs?

RobDapice | Posted in PassivHaus on

Insulation: two layers of 3″ Roxul Comfortboard IS
Wood sheathing and wood framed construction.
Two story residential project.

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  1. GBA Editor
    Martin Holladay | | #1

    Use cap nails (which are available in lengths up to 8 inches) to hold the insulation in place temporarily. Then install vertical 1x4 furring strips with long screws; the furring strips will hold the Roxul securely.

    For more information on sources of long screws, see How to Install Rigid Foam Sheathing.

  2. albertrooks | | #2


    We love tough applications like this.

    Martin shows the cap nail to hold the Mineral Wool in place. For applying the batten, here is the layout (with a brief explanation) for a project that we are working on that uses 6" of MW on a wood framed wall. In this project, the batten is a fire treated 2x4. Consider using a 2x4 for your project also. The extra thickness of threaded fastener into the batten is good to support high wind loads. The combination of straight and angled screws is essentially creating a truss system. The design loads in the attachment meet current Central European code. It's too bad that we have to "borrow" from across the pond for both the fastener and the application knowledge, but they've been adding MW Insulation to the exterior of buildings for a long time and we (the US) are just starting.

    The tough part of applying MW is that it compresses as you screw down the batten. These fasteners are used because they have a thread pattern that will not compress the MW. here is a link to a quick test that we did for 6" MW:

    Here is the link to the fastener in our webstore:

    Email us if you need help: info[at]

  3. user-212218 | | #3

    That seems overly complex Albert. I was under the impression the BSC chaps had tested similar insulation depths with a much simpler screw layout...

  4. albertrooks | | #4


    Yes this is more complex than what one can do with rigid foam. With foam you can use compression, but mineral wool will compress so you have to apply a batten that will take the shear loads, but without compressing the MW.

    Harder than it seems and especially so as it gets thicker. At least in my experience.

  5. RobDapice | | #5

    Thanks very much for your responses. I have been introduced to the Heco screw products, they look great (but expensive) for fastening the battens. I was wondering more specifically about the best way to hold the mineral wool up until the battens are in place; cap nails may work in spite of the compression; a technical rep from Roxul recommended Insulfast by Ramset ITW, but again, it's quite expensive and it is off-label in the sense that it is intended for concrete or CMU and my framing and sheathing is wood.
    Again, thanks for everyone's help.

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