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[Cob] rubble trench foundation questionsAmanda Peck ap615 at hotmail.com
Sun May 1 17:57:34 PDT 2005
I don't have a good handle on what you need structurally. The time I did one, the drain--only about 18 inches down--did drain to daylight, which is the whole point of having a drain there. On top of that we tamped smalish gravel until the ground rang, then foundation/stemwall, then building. But our posts were a couple of feet OUTSIDE of the building so the overhang was well supported. So far, it's OK, and it was log, not straw bale, and we are having fewer and fewer serious winters (now that I've said that, I may be able to try out the snowshoes next year!). My soil was a mixture of silt blown many hundreds of miles from the Dust Bowl (according to the septic tank inspector) and rocks. Check on AGS or PAHS. AGS isn't so space-consuming. The idea is that you use up summer heat in the winter, when you run cold in for the summer. www.greenershelter.com ......... James wrote: Hi, here in N central Washington we are building a post and beam straw bale house with cob interior walls and floor. Local inspector okayed a 2'X2' rubble trench foundation with 4"drain pipe, with the posts on 10"X34"X34" footings integral to the inside edge of this trench, but when we started digging we found one corner of the house 2' lower (so our "trench" ended being at grade!) We plan to berm it with 2' of loam up against the 3' of 2" rigid foam on the outside surface (top 1' being a 12" X16" bondbeam), and have gravel on the inside (sub floor - insulated only for the first 8' on the southside of the living rm. with 2" foam under the floor). My question is; should Can you run we dig deeper on the low side (hard to do at this point, and just increasing the thermal mass more - see concern below)? or insulate more (1"X24") with a winged/skirt around the whole perimeter(expensive but doable)? Some factors; the site is dry but on fine clay below 2' of loam, I'm conerned about the trench and the post footings being just on this loam. I'm also conerned about the increased thermal mass that the extra gravel fill has added to the house. Should I insulate under the whole house to reduce this mass (with 1.5" foam)? - we have a great passive solar site but it is the great NW after all and often snowy/cloudy in the winter with temps down to -35 F.... I'm worried about the house becoming a cold heat sink, only a good thing in the 100+ degree summers. Any thoughts, or similar experiences? Thanks for your help - in advance! James
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