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Anyone have experience with sub-slab bagged-perlite?

AdamPNW | Posted in Green Building Techniques on

Hi all, I was planning to use a foamed-glass aggregate product for my sub-slab insulation since it has low embodied energy compared to other options in this application. However being on the west coast, the shipping cost was astronomical.  I’m considering using bagged perlite as an alternative product since it also has low embodied energy.

According to the Perlite Institute (see attached), it comes in 4 cubic ft paper bags which are laid flat and compacted, creating an 8” lift with R-value of 25. 
The installation detail shows that the vapor barrier can be installed either above or below the perlite. Recent posts on GBA suggest the vapor barrier should ideally be placed above the insulation, but I’m concerned that paper bags outside the envelope (below the vapor barrier) would attract unwanted pests (carpenter ants, in my area).  

Does anyone have experience or thoughts on this application of perlite?



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  1. AdamPNW | | #1

    An additional detail: the slab will be concrete-free (earthen clay floor), so there won’t be very much bleed water to worry about from above.
    Another alternative is to request plastic bags for the perlite, and keep the vapor barrier above them. The plastic is probably going to break down over time and possibly settle a tiny bit.
    So option 1: paper bagged perlite with vapor barrier installed below.
    Or option 2: plastic bagged perlite with vapor barrier above.
    Any thoughts are appreciated,

  2. Erikas | | #2

    I don't have an answer for you, but random thought: have you considered using diamateous earth instead? Pretty good thermal properties; should compact relatively well (especially if you source the finer grained versions); and provides natural insect protection (and could go below vapor barrier). I've never heard of it being used for this application, but I've thought of using it as wall insulation myself. Potential downside is that it will absorb a lot of moisture which, depending on your view, may be either a positive or a negative.

    Can be sourced in bulk relatively inexpensively (I bought a pallet from Grainger a few years ago mostly for my garden).

    Just a random thought.

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