I'm looking to build an earthsheltered PSP style building. Perhaps a dumb question, but if I'm already below the frost line why sink posts at all? Couldn't one use sill beams instead? I'm guessing that in an Oehler building, sinking the posts helps to resist the pressure from the earth but if the sill beams are sufficiently squared and shored and the posts are tied into the sills very securely why would sinking posts be preferable? With sill beams I could almost eliminate direct ground contact.