Morgan Caraway wrote:The cheapest foundation is no foundation. We're currently building a house without a rubble trench foundation. We are berming almost all of it. This protects the structure from frost heaving. There will, of course, be a drainage pipe in place around the bottom of the wall to avoid water build up.
Expansive soils are present throughout the world and are known in every US state. Every year they cause billions of dollars in damage. The American Society of Civil Engineers estimates that 1/4 of all homes in the United States have some damage caused by expansive soils. In a typical year in the United States they cause a greater financial loss to property owners than earthquakes, floods, hurricanes and tornadoes combined.
Even though expansive soils cause enormous amounts of damage most people have never heard of them. This is because their damage is done slowly and can not be attributed to a specific event. The damage done by expansive soils is then attributed to poor construction practices or a misconception that all buildings experience this type of damage as they age.
Terry Ruth wrote:
To mitigate these issues first off, foundations should be placed on “undisturbed” (not tamped that has low compression and needs to settle over decades) soil per code. This soil type at a minimum has to be able to react the building loads based on its compression strength, preferable shear too. Code has soil compression allowables. If the soil lacks the min. properties it has to be modified, some use a road base to minimize the compression differences, which also makes a good base for rubble trenches. Rubble trenches also provide a capillary break that is needed somewhere, on the foundation or any berm.
3000-10,000 PSI concrete foundation or bedrock provides the highest resistance to building loads and settling ~ 12,000 PSI, or pile drivers to bedrock, although if the mix or sub-soil is not right will still see settling issues.
We dig to frost depths in hopes of finding high PI soils with large water holding capacities that keeps dynamic forces away from foundations. The depth is a function of PI.
“No foundation” with the unknowns denoted above assumes major risk known to mankind all over the world for centuries; one does not have to look far on the internet alone to find. I wish you luck and hope you set it on a strong low PI soil at a minimum.
Morgan Caraway wrote:When I say "no foundation," I of course mean "no traditional foundation." Basically, what I'm building is an earthbag earthship. The house is being built on compacted sub-soil. In areas where soil has been disturbed, there will be a footer to the compacted sub-soil supporting posts above. The bermed part of the wall be insulated to minimize condensation. The layer of gravel is thin, enough to minimize capillary action. Will what I'm doing work? Do earthships work? That being said, I'm happy to post updates.