An accessory dwelling unit (ADU) is one of the smartest ways Arizona homeowners are adding space, housing family, and generating rental income. But the first question is always the same: what does an ADU actually cost? The honest answer is "it depends" — but the ranges below will give you a realistic planning budget for the Phoenix East Valley.
ADU cost ranges in Arizona
Most ADU budgets in the East Valley land somewhere in these bands. Detached units cost the most because they need their own foundation, roof, and utility runs; converting existing space is the most affordable path.
| ADU type | Typical size | Ballpark cost |
|---|---|---|
| Garage conversion ADU | 300–500 sq ft | $60,000 – $130,000 |
| Attached ADU (addition) | 400–700 sq ft | $110,000 – $200,000 |
| Detached ADU / casita | 500–900 sq ft | $150,000 – $300,000+ |
What drives the price
- Size and whether it's detached, attached, or a conversion
- Kitchen and bathroom count and finish level
- How far utilities (water, sewer, electric) have to run to the unit
- Site conditions — grading, access for equipment, and existing landscaping
- Permit, plan, and impact fees for your city
- Whether you need separate utility metering for a rental
Does an ADU add value in Arizona?
Generally, yes. An ADU adds livable square footage and a potential income stream, both of which appraisers and buyers value — especially in high-demand East Valley cities like Gilbert, Chandler, and Mesa. Many homeowners treat the rental income as a way to offset the build cost over time. Actual returns depend on your lot, the finish level, and local rental demand.
Permits and Arizona ADU rules
Arizona has moved to expand ADU allowances, but the specifics — setbacks, size caps, parking, and owner-occupancy — still come down to your city and lot. Before you fall in love with a design, it's worth a feasibility check so you build something your property actually allows. A licensed general contractor handles the plans, permits, and inspections so the unit is legal and financeable.
Related services & areas
Planning a project in Gilbert or the East Valley?
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