ADU Cost Guides for Every State

Why ADU Costs Swing by $500K Across States

The same detached ADU costs roughly $70,000 in rural North Dakota and $600,000+ in coastal California — and it's rarely just labor rates. Frost depth pushes foundation costs up in the Northeast and Mountain states, where footings have to go 36–60 inches down instead of a standard slab. Expansive clay soils across much of Texas and the Southwest call for engineered foundations most other regions skip. And a state's own ADU law matters as much as its climate: California's AB 2221, Oregon's HB 2001, and Montana's HB 382 all mandate ADUs "by right" in most zones, while states with no statewide law leave the decision entirely to individual cities — meaning two towns 20 miles apart can have completely different rules.

Every figure in the grid below comes from the same state-level guide linked from each card — regional labor data, permit-fee benchmarks, and the specific law or zoning quirk driving that state's range. Click through to a state for city-by-city numbers, or use the region jumps above to compare a specific part of the country.