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Community and Q&A

Alternatives to Rigid Insulation on Exterior on Existing Walls

andreacmichael | Posted in Green Building Techniques on

I work on a lot of renovation projects (in Montana, Climate Zone 6B) where we need to add insulation to exterior walls and I typically spec 2-3″ of rigid mineral wool or wood fiber insulation over Soletex Mento housewrap with a rainscreen but am now have an incredibly difficult time sourcing those materials in our region. (It’s always been difficult but now seems all but impossible) Does anyone have a suggestion for an alternate approach to adding exterior insulation that is not foam and that is reasonably comparable in cost to the above described assembly.  Thanks!

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  1. kyle_r | | #1

    I saw someone post some questions about the Cascadia Clip system a while back. It’s a type of clip/furring strip system that allows you to install rock wool batts on the exterior of sheathing. I have no idea how well it works or the cost, but might be worth looking into.

  2. kbentley57 | | #2

    You may be able to get away with semi-rigid fiberglas panels. The OC type 705 is a 6.0 lb/cu.ft. fiberglas insulation that could work. Its compressive strength is about 1/5 that of comfortboard, so you'd have to be careful on the installation.

    There are other methods, as Kyle R mentioned.

    Just toying with a thought here, but safe n' sound seems to be available in different markets. a 2x4 on edge would provide an attachment point for the siding, allowing the 3" batt to be installed between the 'studs', leaving a 1/2" air gap for the rain screen. The thermal performance of the 3" safe n sound with a 3.5" of wood, is probably somewhere on the order of a thermally broken 2" wool installation, for the whole wall assembly. Attach it with the same Rodenhouse washers, or similar, etc.

  3. Jon_R | | #3

    > wood fiber insulation over Soletex Mento housewrap

    So water that makes it through the siding can wet the wood fiber insulation? Is there proof that it holds up to this, long term?

    Is water retention and then inward vapor drive an issue with fiberglass outside of WRB? Or even mineral wool?

    A little discussion here:

  4. Expert Member
    Akos | | #4

    You can look at roofing high density fiberboards. These can be ordered in 1", 1 1/2" and even 2" and are typically R2.5/inch. These are not always stock item and you might have to order a full bundle.

    Try Fibertop or Structodek HD.

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