How Much Does an ADU Really Cost in 2026? City-by-City Data

ADU construction costs vary wildly depending on where you live — from $80K for a garage conversion in Tucson to $400K+ for a detached unit in San Francisco. We analyzed real cost data across 50 cities to give you the most accurate picture of what an ADU will cost in 2026.

National Average: What to Expect

Across our 50-city dataset, the average ADU construction cost in 2026 is $150,000-$300,000 for a detached unit, $80,000-$180,000 for a garage conversion, and $100,000-$250,000 for a prefab ADU. Per-square-foot costs range from $150 in affordable markets to $450+ in high-cost metros.

Most Affordable Cities to Build an ADU

If you are looking for the lowest construction costs, consider cities in Texas (Houston, San Antonio, Fort Worth), Arizona (Tucson, Phoenix), and the Southeast (Jacksonville, Charlotte). These markets offer per-square-foot costs well under $250.

Most Expensive Cities for ADU Construction

San Francisco, Boston, and New York City lead the pack for ADU construction costs, with per-square-foot pricing regularly exceeding $350-$450. High labor costs, expensive permits, and complex building requirements all contribute.

Hidden Costs Most Homeowners Miss

Beyond the construction quote, budget for: sewer and water connection fees ($5,000-$15,000), impact fees (waived under 750 sq ft in CA), electrical panel upgrades ($2,000-$5,000), site grading and tree removal, and landscaping restoration. Add 10-15% contingency to any estimate.

Prefab vs. Stick-Built: The Real Cost Comparison

Prefab ADUs promise 20-40% savings over traditional construction, but the reality is more nuanced. While the unit itself may be cheaper, site prep, foundation, and utility connections are similar costs. Total installed prefab cost averages $100K-$250K vs. $150K-$350K for stick-built.