ADU Cost Report: What an ADU Costs in Q3 2026
Our quarterly snapshot of ADU construction costs — cost per square foot by state, how ADU type and finish level change the math, and where the money actually goes.
About This Report
This is our quarterly ADU cost snapshot — the same estimates that power our ADU Cost Calculator, published as a reference you can skim. Each quarter we re-verify these ranges against contractor pricing and update both the calculator and this report together, so the numbers you see here always match what the calculator produces.
This Q3 2026 edition is the first in the series and establishes the baseline. Future editions will note what moved and why.
For the full methodology and a deeper dive on each cost category, see the complete ADU Cost Guide.
Cost Per Square Foot by State — Q3 2026
Base construction cost for a detached ADU at a standard finish level. Attached units, conversions, and JADUs run meaningfully cheaper (multipliers below).
| State | Cost per sq ft | 600 sq ft detached ADU |
|---|---|---|
| New York | $300–$520 | $180,000–$312,000 |
| California | $280–$480 | $168,000–$288,000 |
| Washington | $220–$400 | $132,000–$240,000 |
| Oregon | $210–$390 | $126,000–$234,000 |
| Colorado | $210–$380 | $126,000–$228,000 |
| Nevada | $190–$340 | $114,000–$204,000 |
| Illinois | $180–$330 | $108,000–$198,000 |
| Arizona | $160–$300 | $96,000–$180,000 |
| Florida | $160–$310 | $96,000–$186,000 |
| Texas | $150–$290 | $90,000–$174,000 |
| U.S. (other states) | $175–$340 | $105,000–$204,000 |
The coasts remain the expensive places to build. New York and California carry the highest labor and permitting costs; Texas, Arizona, and Florida stay the most affordable of the major ADU markets.
How ADU Type Changes the Price
New square footage is what costs money. Anything that reuses an existing structure — a garage, a basement, a spare bedroom — skips foundation, framing, and roofing, and the price drops fast:
- Detached ADU — the baseline (100% of the costs above)
- Attached ADU — roughly 15% less (shares a wall and often utilities)
- Garage conversion — roughly 40% less (structure already exists)
- Junior ADU (JADU) — roughly 58% less (converts existing interior space, under 500 sq ft)
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In California, that means the same "ADU" label can describe a $35,000–$60,000 JADU or a $168,000–$288,000 detached build. If budget is the constraint, start with our garage conversion guide or the JADU guide.
Finish level swings the total further: budget finishes run about 18% below the standard ranges above, and premium finishes about 32% above.
Where the Money Goes
Construction is only about two-thirds of an ADU budget. The typical breakdown:
| Category | Share of budget | On a $200,000 project |
|---|---|---|
| Construction | 65% | $130,000 |
| Site work & utilities | 12% | $24,000 |
| Design & architecture | 10% | $20,000 |
| Permits & fees | 8% | $16,000 |
| Contingency | 5% | $10,000 |
The most common budgeting mistake is quoting the construction number and forgetting the other 35%. Utility connections in particular vary wildly by lot — a long trench to the sewer main or a panel upgrade can add five figures before a wall goes up.
Does the Cost Pencil Out?
Cost is only half the equation. Whether an ADU is a good investment depends on the rent it can earn and the value it adds at sale:
- Model your rental income and payback period with the ADU ROI Calculator
- See what the research says about resale in Does an ADU Increase Property Value?
- Compare ways to fund the build in our ADU Financing Options guide
Get a Real Number for Your Project
State averages are a starting point, not a quote. For an estimate tuned to your state, ADU type, size, and finish level, run the ADU Cost Calculator — then get 2–3 bids from local builders in our contractor directory to see where your lot actually lands in the range.