Know what your adu should cost
A 600 sq ft adu costs $133,200 to $226,800 in 2026, about $300 per sq ft installed. Across every option it runs from $66,000 (junior adu) to $258,000 (detached new build).
Four questions gets you an itemised range, adjusted for construction wages where you live. The whole number, up front, before we ask for anything.
What adu work costs in 2026
| Project | Typical range |
|---|---|
| Junior ADU Carved out of the existing house, shares some services | $66,600 – $113,400 |
| Garage conversion ADU Existing slab, walls and roof already there | $79,900 – $136,100 |
| Prefab or modular Factory-built, craned in, site work still applies | $106,600 – $181,400 |
| Attached new build Shares a wall and some utility runs with the house | $113,200 – $192,800 |
| Detached new build Its own foundation, shell and utility connections | $133,200 – $226,800 |
Where the money goes
Framing and shell
$39,600 · 22% of the job
Electrical, plumbing and HVAC
$28,800 · 16% of the job
Interior finishes
$27,000 · 15% of the job
Foundation and site work
$23,400 · 13% of the job
Kitchen and bathroom
$21,600 · 12% of the job
Permits and impact fees
$21,600 · 12% of the job
Design and engineering
$18,000 · 10% of the job
ADU cost by state
Labour is the part of this job that moves with geography. These are the same 600 sq ft project, priced against construction wages in each state.
- California $139,300 – $237,300 +4.6% vs national
- Texas $135,000 – $229,800 +1.3% vs national
- Florida $125,200 – $213,200 -6.0% vs national
- New York $139,000 – $236,800 +4.4% vs national
- Alaska $148,400 – $252,800 +11.5% vs national
- Alabama $127,400 – $217,000 -4.4% vs national
- Arkansas $122,000 – $207,600 -8.4% vs national
- Arizona $131,900 – $224,700 -0.9% vs national
- Colorado $133,400 – $227,200 +0.2% vs national
- Connecticut $138,000 – $235,000 +3.6% vs national
- District of Columbia $142,600 – $242,800 +7.1% vs national
- Delaware $130,600 – $222,400 -1.9% vs national
Questions homeowners ask
How much would it cost to build a 600 square foot ADU?
A detached new build at mid-range finishes runs roughly $133,000 to $227,000, with $180,000 typical. Converting an existing garage to the same size is far less, around $108,000, because the foundation, walls and roof are already there.
What type of ADU is the cheapest?
A junior ADU carved out of the existing house, at roughly $90,000 for 600 square feet, because it shares walls and services. A garage conversion is next at about $108,000. A detached new build is the most expensive because it needs its own foundation and utility connections.
Is it cheaper to build an ADU or buy a prefab?
Prefab is usually cheaper on the unit itself, about $144,000 for 600 square feet against $180,000 built on site, but the saving is smaller than the sticker suggests. Foundation, utility trenching, crane access and permits are the same either way.
How much does it cost to build a 1,200 sq ft ADU?
Around $266,000 to $454,000 for a detached build at mid-range finishes. At that size you are building a small house, and impact fees in particular climb steeply, some jurisdictions waive them below a size threshold you would have just crossed.
Reviewed and maintained by Anchorcost. Last checked September 3, 2026. Figures are verified against this page's own calculator on every build. How these figures are worked out.