Updated Straw Bale Wall Section Detail
Option A is a system discussed in the latest "The Last Straw" issue called "Straw Cell" Wall System. It involves constructing the building shell in a very conventional manner and then tying the straw bale to the inside of the wall. The exterior is sheathed and sided in conventional way. The interior is plastered straw. Cellulose insulation fills the stud cavities. Option B is post and beam framing with straw bale infill. The posts would be "box" columns constructed of studs and the depth of the straw bale. There would be a "bond" beam running the full length of the perimeter with "box" columns spaced about 8'-0" oc. I would expect the beam to be about a 4x8, maybe an LVL. The exterior is plastered with a lime based plaster and the interior is clay based plaster. My initial reaction was that option "A" has completely redundant wall systems, however, upon closer look, it appears that both options would use about the same amount of wood, so I think it's reasonable to consider both. One major disadvantage of "A" is that the walls are thicker 22" rather than 18". This would impact the floor plan, but I feel that this can be accommodated. The big advantage of option "A" is that the conventional framing can be done without a lot of consideration to the straw bale. The roof can be installed prior to the bale assembly. (Although, this may also be true for option "B"). So framing, sheathing, electrical, etc. can all be constructed by subcontractors in the way that they are used to building. Structural and permitting issues would be simplified. Option "B" was developed with the intention of being an efficient hybrid between load bearing straw bale and conventional framing with a post and beam system. The box columns are spaced so straw bale infill can be easily accomplished. It is realtively simple construction, but is not "conventional". In conclusion, I would say that any given choice is never the case of one is right and the other is wrong, but the question is what is most appropriate in this situation.