How Much Does an ADU Cost in 2026?

The national average ADU cost in 2026 is approximately $180,000, with most homeowners spending between $40,000 and $400,000. A basic garage conversion starts around $40,000 to $80,000, while a custom detached unit in a high-cost market can exceed $400,000. The most common scenario — a 600 sq ft detached mid-range ADU — costs $90,000 to $200,000 depending on location. Tariffs enacted in 2024 and 2025 have added an estimated 8 to 15 percent to construction costs nationally.

A garage conversion is consistently the most affordable ADU type, ranging from $40,000 to $150,000 nationally. Because the walls, roof, and foundation already exist, you save $40,000 to $60,000 in structural costs compared to new construction. Basement conversions are similarly cost-effective at $50,000 to $150,000. Prefab and modular ADUs are the next most affordable option, with faster build times and more predictable pricing than site-built units.

Build time depends heavily on ADU type. Garage and basement conversions typically take 3 to 6 months. Attached ADUs take 5 to 8 months. Detached ADUs, which require full foundation, framing, and utility connections, take 6 to 14 months. Permitting is often the biggest variable — California averages 8 to 12 weeks for permit approval, while smaller cities can approve in 4 to 6 weeks. Using pre-approved plan sets can cut permitting time by 40 percent or more.

Yes. Appraisers value ADUs primarily on income potential, and well-built units consistently add 20 to 30 percent of their construction cost to the property value — sometimes more in high-demand rental markets. In cities like Los Angeles, a new detached ADU can add $300,000 or more to a property appraisal. The key factors are location, ADU quality, and local rental demand. Garage conversions still add value, but typically less than purpose-built detached units.

National rental estimates vary significantly by market. In affordable Sun Belt cities like San Antonio or Atlanta, a 600 sq ft ADU rents for $1,000 to $1,400 per month. In mid-tier markets like Denver, Phoenix, or Orlando, expect $1,300 to $1,800 per month. In premium coastal markets like Los Angeles, Seattle, or the Bay Area, a 600 sq ft ADU can rent for $1,800 to $3,200 per month. Detached units command roughly 15 to 25 percent more than attached or converted units of the same size.

Yes, all ADUs require building permits. The permitting process and cost vary significantly by state. California has a streamlined statewide ADU law that limits permitting fees and timelines. Texas, by contrast, has no statewide ADU law — rules are set at the city level, and permit costs range from $3,000 to $4,500 in most Texas metros. Nationally, permit costs range from $1,350 in smaller cities to $25,000 or more in high-cost metro areas. Your general contractor typically handles permit applications.