How Much Does an ADU Cost in 2026?
ADU (accessory dwelling unit) costs span a wider range than almost any other home project — from $40,000 for a prefab studio to over $360,000 for a site-built two-bedroom in a high-cost state. What drives that variance? Construction method matters most: prefabricated ADUs land 20–40% below site-built equivalents. After that, location is the decisive factor. California ADU labor rates run 40–60% above the national average, while Midwestern and Southern markets run 15–25% below.
Utility connection costs, impact fees, and setback requirements add more variability that national averages can't capture. BuildCost applies state-level labor and material indices to give you an estimate grounded in your actual market — so the number you see reflects what local contractors are bidding today, not a number pulled from a national survey three years ago. Enter your size and state to get your free localized estimate.
Get Your Free ADU Estimate
Pre-set to ADU / Guest House — enter your planned square footage and state.
How big is your ADU / Guest House?
A studio ADU is ~300 sq ft. A 1-bed ADU is ~500 sq ft. A 2-bed ADU is ~700–900 sq ft.
Average ADU Cost in 2026
National averages across all U.S. regions. California and coastal metro costs will run significantly higher; rural and Midwestern markets will run lower.
| Type / Size | Low | Mid | High |
|---|---|---|---|
| Studio ADU — prefab (300 sq ft) | $40,000 | $65,000 | $100,000 |
| 1-Bedroom ADU — site-built (500 sq ft) | $75,000 | $130,000 | $200,000 |
| 2-Bedroom ADU — site-built (800 sq ft) | $130,000 | $220,000 | $360,000+ |
Includes foundation, framing, plumbing, electrical, kitchen, and 1 full bath. Utility connection and permit fees may be additional.
What Affects the Cost of an ADU?
- •Construction method: Prefabricated ADUs cost 20–40% less than site-built but offer fewer customization options and may face stricter HOA or zoning limits. Site-built ADUs take longer but can be fully customized to match your home.
- •Size and bedroom count: Each additional bedroom adds full bathroom, kitchen, living area, and egress requirements. Moving from a studio to a 1-bedroom often doubles the cost. Kitchen and bathroom fixtures are the most expensive line items per square foot.
- •Location and labor rates: California, New York, and Hawaii ADU labor rates run 40–60% above national averages. Texas and the Southeast run 15–25% below. Your zip code is the single biggest variable in any ADU estimate.
- •Utility connections: Connecting a detached ADU to water, sewer, and electrical can cost $10,000–$30,000+ depending on distance from the main home and local utility requirements. Garage conversions avoid most of these costs.
- •Permits and impact fees: ADU permit fees range from $3,000 to $20,000+ depending on jurisdiction. Some cities have waived or capped fees for ADUs under 750 sq ft. Check your city's ADU fee schedule before budgeting.
ADU Cost — Frequently Asked Questions
How much does an ADU cost?
An ADU (accessory dwelling unit) typically costs $40,000–$360,000 depending on type, size, and location. A prefab studio ADU starts around $40,000 installed. A site-built 1-bedroom ADU averages $100,000–$200,000. A fully custom 2-bedroom ADU in a high-cost market like California can exceed $360,000. The biggest cost driver is whether you choose prefabricated or site-built construction.
How much does an ADU cost in California?
In California, ADU costs run 40–60% above national averages due to high labor rates, strict Title 24 energy code requirements, and impact fees. A studio ADU in the Bay Area or Los Angeles typically costs $150,000–$250,000 site-built. Sacramento and the Inland Empire average $100,000–$180,000. California has streamlined ADU permitting since 2020, but fees and labor still push costs above the national range.
How long does it take to build an ADU?
A site-built ADU typically takes 6–12 months from permit application to move-in. Permitting alone can take 2–4 months depending on the jurisdiction. A prefabricated ADU can reduce construction time to 8–16 weeks once the permit is approved and foundation is ready. Detached ADUs generally take longer than garage conversions.
Does an ADU require a permit?
Yes — all ADUs require a building permit covering foundation, framing, electrical, plumbing, and mechanical systems. California law (AB 68, SB 13) has streamlined ADU permitting to reduce delays, but permits are still required statewide. Most jurisdictions require plan review and inspections at key construction milestones.
How do I find a contractor for an ADU?
Look for contractors who specialize in ADUs or accessory structures, not just general remodelers. ADU-specific builders understand local setback rules, title 24 requirements, and utility connection processes. Ask for 3+ bids, verify ADU project references, and confirm the contractor will manage permitting. Thumbtack and specialized ADU builder networks are good starting points.
Ready to Find a Contractor?
Use your estimate to vet bids, then connect with vetted ADU builders in your area through Thumbtack — free quotes, no obligation.
Related Cost Calculators
Cost Estimates by Location
Also see: ADU Cost Guide · ADU cost by state · All cost calculators