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Community and Q&A

Fasteners for mineral wool to foundation walls?

user-1120876 | Posted in Energy Efficiency and Durability on

I am planning to insulate the exterior walls of a building with a walk-out basement. The building will have wood studs for the first floor and concrete walls for the basement.

Originally I was planning to use ICFs below grade and foam board above, but became concerned about possible damage by carpenter ants and the need to install gypsum board on the interior.

My current plan is to install 6″ of mineral wool on the exterior. I plan to use furring strips with long screws through the insulation to the studs on the first floor, but I am not sure how to fasten the insulation to the concrete foundation walls. I see metal screws as having two problems. First, they would penetrate the waterproofing membrane and second, they would provide thermal bridges to the concrete walls.

Any thoughts on this?

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  1. GBA Editor
    Martin Holladay | | #1

    Plasti-Grip PMF fasteners would probably work. Read about them here: New Green Building Products.

  2. user-1120876 | | #2

    I looked at the Plasti-Grip fasteners earlier, They sounded just right except for the fact that they only come in lengths up to 5 3/8" long.

  3. jinmtvt | | #3

    Stephen: why are you afraid that carp ants will get in the icf walls ??
    There has been a few discussion here on that topic, insecst and exeterior insulation.
    Although i rremember no definite solution, you can easily block out car ants using only
    peel stick membrane, flexible parging , dimpled membrane etc...

    how do you propose to protect your mineral woold from water ??
    you furring strips ??

    if you fill up with sand, carp ants don't dig much in most sand, thus you only need to really protect them from reaching higher than the protected walls above grade
    ( extend membrane a few ft from the ground and provide correct ant flashing )

  4. user-1120876 | | #4

    Thanks for your input.

    I guess I haven't been convinced that the solutions posted since the Journal of Light Construction (JLC), October 1998 article on termites and carpenter ants in ICFs and foam insulation are sufficient. I plan to use foam below my basement slab, but even that makes me a bit nervous. Also, while we don't have much in the way of termites ( per the IRC slight to moderate in the part of zone 7 I will be building), it sounds like they are moving north (global warming?)

    As far a protecting the mineral wool from water - I would be using Roxul drainboard which would be protected by siding or flashing above grade and with no protection below grade (other than the sand backfill to prevent silting. The furring strips would only be used behind the siding above grade.

    I have other reasons to not use ICFs, but that is another discussion.

  5. BillDietze | | #5


    I too don't like the foam for the same reasons. Have you considered adhesives on the drainboard below grade? Perhaps a low expansion polyurethane foam. Not dissimilar to how some people attach foam below grade to a foundation wall... I've been wondering about a similar detail myself, but I haven't yet settled on a solution - need to mock something up.

    Tremco had (has?) a solution for the first layer of insulation: apply the warm-n-dri board to the wall before the sprayed on waterproofing membrane dries. But in your case the next layer (of drainboard) would require something else to hold it in place that is where the adhesives come in. The remaining problem is then covering the two/three layers of drainboard immediately above grade vs. the compression of the drainboard below grade - not pretty is my guess.

  6. user-1072251 | | #6

    30 yr old house with 5" of parged XPS & EPS. To my surprise there were no sign of insects, just a rodent highway & pink evidence that there are interior wall off ramps, all well hidden.

  7. user-1120876 | | #7

    Reply to Bill and Bob
    I considered adhesives below grade, but am a bit doubtful that mineral wool will stick that well to mineral wool. Let me know if you get around to doing a mock-up. Above grade I'm looking at siding to cover it, except for the 8 inches I want between the bottom of the siding and the ground. but this would still leave the problem of screws as thermal conductors.

    Thanks for the additional worry. From some BSC posts I thought that the mineral wool would be pretty durable and insect and rodent resistant, but then I saw a GBC post about birds building nests in the stuff before the siding went on. Your post makes me wonder how rodent resistant it would really be. Ah, well, the search for the "perfect" wall goes on.

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