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Community and Q&A

Perlite insulation?

Stuart Miller | Posted in Green Products and Materials on

Mineral wool is a popular insulation recommendation, but it seems expensive and has limited supplier options. I came across some info on perlite (and even vermiculite and lightweight expanded clay aggregate [LECA]) as a potential insulation material. I realize that it has a lower R-value per inch than others (perlite loose fill at 2.7/in, vermiculite 2.08/in), but if wall thickness were not a limiting factor, would it be a worthwhile consideration?

What if, for instance, you wanted to fill between AAC blocks or panels or a double wythe of concrete? Would perlite (or vermiculite/LECA) be a more cost effective alternative to mineral wool? Could it compete with rigid foam or cellulose? Would filling wall cavities be relatively low-labor?

There are properties of mineral wool that seem particularly attractive, and I’m wondering if these other minerals would provide the same. They would be similarly non-combustible and inorganic (no substrate for mold or termites), but I wonder if they would also have favorable properties for moisture or mass/lending any structural rigidity or strength.

I haven’t investigated very much yet, partly because communities like GBA don’t seem to ever mention these…which leads me to wonder if there are some major reasons to discount them.


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  1. Expert Member
    Dana Dorsett | | #1

    Perlite is fairly hygroscopic (which is why they add it to potting soil) and not very air retardent, but sure- with the appropriate air barriers, vapor retarders, capillary breaks, and wall thickness just about anything works. (Pumice, anyone?) Don't count on it for adding structural capacity though.

  2. GBA Editor
    Martin Holladay | | #2

    Q. "Would perlite (or vermiculite/LECA) be a more cost effective alternative to mineral wool? Could it compete with rigid foam or cellulose?"

    A. No and no (I suspect). But why don't you build a house with perlite and keep track of your costs? Then you can write a guest blog on the topic for GBA.

    Q. "Communities like GBA don't seem to ever mention perlite insulation."

    A. Here are some GBA links to get you started:

    Building a Foam-Free House

    Foam-free builds

    Does a viable (performance and cost effective), non-foam option exist for under slab insulation?

    Perlite compressive strength?

    Perlite as insulation

    Perlite for walls vs Dense pack Cellulose

    Perlite vs. rigid foam insulation

    -- Martin Holladay

  3. Stuart Miller | | #3

    Thanks for the answers. What may perhaps be a bit different about my question from those others is the wall cavity use (rather than under foundation) and contained within masonry (as opposed to traditional wood frame, sheathing, and drywall).

    But it really sounds like dense packed cellulose has a strong cost lead over every other option available.

    Though foam is favored for exterior to wall (for ease of creating a continuous exterior insulation envelope), under slabs, and perhaps on roof assemblies where the attic space is functional (rather than loose fill).

    I tend to favor all-mineral assemblies and shy away from cellulose because of prejudices with regard to flammability and an organic substrate feeder for mold or insect infestation, settling, and longevity...
    Are those really unfounded concerns?
    If inside a concrete or AAC sandwich for the wall?

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