Can a Slab Foundation be Insulated Without Rigid Foam?
That’s essentially the question posted by Roy Harmon in a post in the GreenBuildingAdvisor Q&A forum.
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Specifically, Harmon is wondering about something called the Archibio Sandwich Slab, which is described in a 1994 book entitled Straw Bale House. It consists of two layers of concrete with straw bales between then. Although the technique is said to require more concrete than a conventional slab foundation, the cost of the insulation itself is low, $1 or less per square foot for R-50 performance.
Low cost is good, and so is the fact that no petrochemicals are involved. But the organic nature of straw raises concerns, too, chief among them the potential for decay.
Read the whole article at GreenBuildingAdvisor.com.
To avoid rot, straw bales must be kept dry. Lucas Durand calls this a "concept sketch," and appends a few caveats: "This idea is less than half-baked. There are many unresolved issues that I haven't thought about - like air sealing, attachment of rainscreen cladding over parging, the drying potential of the under-floor insulation, etc."