What It Really Costs to Build an ADU in Arizona
Building an Accessory Dwelling Unit (ADU) in Arizona can open up new possibilities—for family living, extra income, and smarter use of your property.
But the first big question every homeowner asks is: How much will it cost?
Here’s a clear, straightforward breakdown of what you can expect—and why investing in a well-designed ADU could be one of the best decisions you make.
Average Cost Range for an ADU in Arizona
While every project is unique, building a new 1,000 sf ADU in Arizona typically costs between $150,000 and $300,000 depending on size, location, design complexity, and site conditions.
Key factors influencing cost include:
- Size: Larger ADUs cost more (naturally). Detached units typically cost more than garage conversions.
- Type: Detached new builds vs. garage conversions vs. attached units.
- Site conditions: Easements, grading, utilities access.
- Finishes and upgrades: Luxury kitchens and high-end finishes increase costs fast.
- Permitting fees: Vary by city or county.
Quick Budget Snapshot
The cost of building an ADU can vary widely depending on the type of structure, site conditions, and level of finish. Here’s a quick look at different ADU types and their typical costs in Arizona as of 2025.
| Type of ADU | Size Range (SF) | Estimated Cost Range | Notes |
|---|---|---|---|
| Garage Conversion | 300–500 SF | $75,000–$140,000 | Lower structural cost, upgrades needed (insulation, utilities) |
| Attached ADU (Home Addition) | 400–800 SF | $125,000–$220,000 | Shares foundation/walls, moderately lower cost |
| Detached Custom ADU | 600–1,200 SF | $180,000–$300,000+ | Standalone structure, highest flexibility (and cost) |
| Shipping Container ADU | 320–640 SF | $90,000–$180,000 | Depends on container quality, retrofitting, zoning, and finishes |
Pro Tip: Detached ADUs offer the most flexibility, but also involve more site work (utilities, setbacks, foundations), which impacts cost.
Note: All costs shown are estimates based on typical 2025 Phoenix-area market rates. Your project’s cost will vary depending on site-specific factors, finishes, and jurisdictional requirements.
As you can see, there’s no one-size-fits-all answer. A garage conversion or shipping container ADU might make the most sense for some properties, while others are better suited for a detached custom build.
Beyond Construction: Other ADU Costs to Plan For
Building costs are just part of the picture. Make sure you also budget for:
- Permitting fees: ($5,000–$10,000+ depending on jurisdiction)
- Utility upgrades: (electric, water, sewer)
- Architectural and engineering plans: ($5,000–$15,000+ for custom)
- Impact fees or special assessments: (depending on city/county)
How an ADU Can Pay Off Over Time
An ADU isn’t just an expense—it’s an investment.
ADUs can provide:
- Long-term rental income ($1,000–$2,000+ per month depending on location)
- Added resale value (estimates range from 20% to 30% property value boost)
- Housing flexibility for family or aging parents
- Smarter property use without needing to move
Over time, a well-designed ADU can pay for itself while strengthening your family’s financial security and flexibility.
PlanHAUS: Helping You Budget Smarter, Build Smarter
At PlanHAUS, we believe smarter planning leads to better results.
We help Arizona homeowners understand real costs up front, design ADUs that fit both budget and zoning, and navigate the permitting process without surprises.
Whether you’re looking for a custom design, a pre-designed plan, or a full-service solution—we’re here to help you move forward with clarity.
