[GSBN] Under slab and edge insulation at doorways

[Kelly Lerner]

Thanks all for your thoughts on perlite underslab insulation!

Here's the document that I found after a discussion with Laura Bartels (who, I think, used perlite under her adobe slab in Carbondale, CO). That's what got me started down this exploration path.
http://www.perlite.org/product_guides/21%20perlite%20for%20underfloor.pdf

It specifies a water repellant type IV perlite and I will have to check out whether that is available in Spokane. I was also planning on putting 6 mil poly directly under the slab (and wrapping it up the edge), so that the slab is isolated from ground water and radon intrusion. We tend to have dry, well-drained soils in Spokane due to the gravel left by the Missoula floods. Finally, I was going to leave the perlite in bags to aid in the compaction. I think that before I try this on a foundation, I may get a bag of perlite, play with compaction and then  bury it in my backyard under a tree for a few months, then dig it up to check out the capillary action and moisture. 

On the slab edge detail, Chris, I never do a monolithic pour. I usually use a floating slab within a conventional stemwall with footing (no big seismic concerns in Spokane, yet). The joint between stemwall and the slab falls under the bale wall and that's where I typically wrap insulation up the edge of the slab. The problem comes at the doorways. What I decided yesterday, was to shift the door location in about 3" so that the threshold will cover the insulation joint. 

I'll keep exploring the perlite, but may stick with high density EPS for underslab now on client projects until I can confirm perlite's performance.

Kelly "KISS" Insulation Maven

> 
> 
> 2011/2/8 Kelly Lerner <klerner at one-world-design.com>
> Hi all,
> In an effort to get away from the global warming potential of and fire retardants in rigid insulation, I'm beginning to design with compacted perlite as under-slab insulation in strawbale houses in Spokane, WA (east side of WA - cold winter - 6800 heating degree days, high desert, dry - about 16" rain/year, water table is usually quite low and soils are well drained). 
> 
> I've found a relatively local source for perlite(Portland) and the costs for R-value are comparable to or less than rigid insulation. I'm installing perlite under the slab and wrapping it up the edge of the slab (on the interior of the stem wall - under the strawbale wall), but I'm having trouble detailing "slab edge insulation" at the door ways. Anyone have any experience or thoughts about the right approach? Contact me on or off list. Thanks!
> 
> In case you're wondering about perlite, here's a link: http://www.perlite.com/faqs.htm
> 
> 
> Kelly Lerner, Architect
> One World Design Architecture
> 509-838-8812
> www.one-world-design.com
> 
> Have you read Natural Remodeling for the Not-So-Green House? Available in Bookstores across the Universe. 
> www.naturalremodeling.com
> 
> 
> 
> 
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Kelly Lerner, Architect
One World Design Architecture
509-838-8812
www.one-world-design.com

Have you read Natural Remodeling for the Not-So-Green House? Available in Bookstores across the Universe. 
www.naturalremodeling.com



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