1-Day Casita Foundation Plans. $749 Flat.

State-approved since May 2026; expansive Blackland clays make the engineered slab detailing earn its keep.

Boxabl’s home state with statewide approval — Clark County inspectors know the product and expect clean anchorage details.

Desert soils (caliche, collapsible pockets) and HB 2720 ADU rights make Arizona one of the fastest permit paths.

Wasatch Front seismic (SDC D) means hold-downs and shear transfer are engineered items on every option.

CID modular pathway plus straightforward permitting in most jurisdictions.

Minimal frost depth keeps foundations economical; coastal counties add wind provisions.

Yazoo clays in central MS are among the most expansive in the country — site-specific slab design matters here.

Moderate frost depth (30–36") drives footing depth; metro reviews are straightforward with stamped plans.

Piedmont red clay and coastal wind provisions — both handled in the engineered detailing.

Coastal counties run high-wind review; Piedmont clays favor properly detailed slabs.

Nashville is one of the most active ADU markets in the South; West TN adds New Madrid seismic detailing.

Karst geology in central KY and New Madrid influence in the west — site-specific design earns its keep.

Slopes and access drive foundation choice — block & pier shines on mountain lots.

Front Range expansive bentonite clays are the defining challenge — engineered slabs matter here.

SDC D seismic west of the Cascades plus the country’s strongest ADU law (two ADUs per lot).

Cascadia seismic detailing west of the mountains; statewide ADU rights make backyard units routine.

State industrialized-building review plus 30–36 inch frost footings — straightforward with stamped plans.

Deep frost (42–60 inches) makes footing depth the core design driver.

Frost depths of 40–48 inches — frost-depth compliance is the recurring plan-review comment we design past.

Frost to 60+ inches and statewide ADU rights under LD 2003.

Deep frost and snow-load country, with ADUs a statutory right on single-family lots.