Single story rear addition approximately 12’ wide over crawlspace. The rear “foundation” was comprised of vertical 2x4’s resting on a single untreated 2x4 placed on the concrete slab. The supporting sill plate is a single thickness 2x4 set flat accross the verticals! Joists are set on the 2x4 "sill’, with noticeable bowing of the 2x4’s. Better yet, some of the sills are only toe nailed to the vertical 2x4’s. This wall is supporting the weight of the shed type roof structure.