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Community and Q&A

Foam-free shallow frost-protected slab Ideas

Thomas K | Posted in Green Building Techniques on

I am considering a shallow frost slab for a new construction 5000 sf (first floor) home in North-West Connecticut (Climate Zone 5b).

I would like to avoid as much foam as possible. Has anyone built a greener version of a shallow frost slab that avoids foam insulation? I know of a 

I am thinking about using Foamglas for the perimeter/footing and exterior “wing” and Glavel for both gravel below the installation and insulation for the entire slab.

Rockwool would be another option (, but I am very intrigued by Glavel as both sub-slab drainage and insulation.

I have seen ads for (just after I posted this question) – maybe that would be an idea, especially since the project has a small basement (for mechanical & storage). So we have to combine slab with basement installation.


Thank you.

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  1. Expert Member
    Malcolm Taylor | | #1


    Make sure the non-foam options you are considering can take the concentrated structural loads imposed by footings, not just the ones experienced under slabs.

  2. Jon R | | #2

    I'm curious, in what way(s) do you consider Foamglas (technically a foam) greener than EPS foam? I'd guess that it takes more energy to produce. Similar for Rockwool.

    1. Thomas K | | #3

      Hi Jon. GBA wrote about this environmental implications of foam vs. Foamglas:

  3. Jon R | | #4

    That link only says one thing about EPS and I understand that it's no longer true.

    1. Charlie Sullivan | | #5

      The issues mentioned are fire retardant chemicals and insect boring it. The fire retardant may have been changed (?) But I am not aware of any truly benign option there, aside from omitting it for below grade use, but I don't know that you can buy that.

      As for insects boring in it I can personally confirm that that was still an issue as recently as this spring, and chipmunks burrowing in it is also an issue, as recently as last week.

  4. Charlie Sullivan | | #6

    As of about 5 years ago they stopped offering foamglas to the building industry, and limited north American sales to industrial applications. But from the site you linked it looks like the have restarted commercial building sales. Which might mean it is possible once again to get it for residential use. I'd make sure you can get it before planning around it. If you can get it I want some too.

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