Welcome! I've visited an Eco-village north-west of my local that was using straw bale for north walls and working with the local authorities to get code changes for a bunch of issues related to them. (Specifically, in the case of straw bale, counting the "inside" measure of the building for permitting, rather than the "outside" so that the builders weren't penalized for the thick walls.) We're very damp in the winter and dry in the summer, so hopefully there will be interesting posts about its ability to moderate humidity - maybe I'd better go look?
Hi Jay, Yes, thick wall construction can be "penalized" because building departments look at a structure's footprint when calculating it's size--which determines both the permit cost and the eventual property tax assessment. And thicker walls = less space inside, a disadvantage for thick wall construction that can be partially offset by designing window seating (to replace free-standing furniture like couches), locate a potted plant, etc. At least one county in California (Sonoma County I think) takes a more progressive approach, measuring the building's interior dimensions and then adding 6" for the exterior wall as if it were built with a conventional framing-insulation system. If more building departments took that approach it would provide incentive for all thicker wall construction, most of which exceeds current code requirements for insulation value.
As for moderating humidity, that's something unique to thick interior clay and lime plasters. Most straw bale buildings have at least a 1" thick, and usually thicker plaster on the inside. In addition to being a thermal storage battery, absorbing heat and releasing it, these plasters have an enormous ability to absorb and release moisture from occupant activities like cooking, showering, and breathing. The plastered walls moderate humidity fluctuations. The straw bales themselves are able to absorb and store quite a bit of water vapor too, but it's important that moisture levels inside the walls not exceed 18% or so--the level at which microbes become active. That's why the plasters must be vapor permeable (what many term "breathable) so any water vapor that makes it all the way through the plaster will be able to either come back out, or pass through the other side of the wall, driven by temperature and vapor pressure.
Jim Reiland wrote:Hi Jay, Yes, thick wall construction can be "penalized" because building departments look at a structure's footprint when calculating it's size--which determines both the permit cost and the eventual property.
Apache County Arizona measures inside to inside and subtracts interior wall thicknesses figuring their square footage. Anything 200 square feet and under doesn't require a permit. Patios screened in or not is not included, lofts are not included. Construction done by the owner regardless of size doesn't require a general contractors license. Earthship construction doesn't require engineered stamped prints but must meet some residential codes for structural integrity, sanitation and egress. They are actually ahead of the Santa Fe NM buzz...
And as an added bonus County Law forbids the Sheriff or any other law enforcement agency including Federal from seriving IRS TAX notices or foreclosure notices which have to be done by the IRS or money institution themselves.