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[Cob] Coblist Digest, Vol 6, Issue 178Barbara Roemer roemiller4 at gmail.com
Mon Dec 22 15:58:32 CST 2008
NRTradiant.com Shody, I like the solar attic, too. We may use the AGS system for our home when we build, having convinced a friend in our climate to provide for it even if she doesn't need it. Ed, your point about earth bermed walls being constructed (usually) of block or concrete is well-taken. concrete has to be waterproofed/isolated or at least damp-proofed with excellent curtain drainage, too, or it will wick water up many stories and into the interior. Berming an earthen or cob wall assures that moisture will migrate, but in contrast to concrete which is not damaged by moisture but does damage by carrying moisture to other materials which are harmed by water, cob will lose its strength as straw in it rots with moisture. The cob must be isolated from the earth berm to keep it dry. Building a berm right near your cob wall but not flat up against it will allow air to circulate and keep moisture from migrating into the cob wall, but it probably doesn't affect the temperature of the room inside the cob wall too much as an open air channel provides neither thermal mass nor significant insulation. Such a berm might keep you more comfortable and reduce drafts as it reduces air pressure from wind against the side of the house, but if that's the order of convection you're working on, you'd do better to caulk the leaks in the wall and save yourself the work of a berm. I'm certainly no expert, but wonder about earth bags and moisture wicking. I've seen earth bags used for foundations with an isolating barrier between them and the cob or bale. The bags around here are woven, so if moisture stood against them, the clay inside would still be able to absorb it. Maybe on a rubble trench with no concrete cap, water would just drain away. We used a concrete cap on the RTF for our little bale shed, and then builder's paper (tar paper) atop that before the bales. I live in a climate with 60" of precip in about five months, so I think about moisture - a LOT. If I lived in an area with 11", I'd be far less concerned about it. Also, of foundation insulation, this source NRTradiant.com states that except for places like California and Nevada, in the US, R10 is usually specified. We will insulate the perimeter well, and run insulation beneath the outer foot or so of the slab, and of course a vapor barrier under it all. Especially in cold climates, where you can create good drainage, the perimeter insulation can be more significant than increasing under floor insulation, and is recommended by RTF builders as well as typical slab/perimeter builders. Barbara