ADU Cost in Arizona in 2026

ADU costs in Arizona in 2026 range from $90,000 for a basic garage conversion in Tucson to $420,000+ for a custom luxury casita in Scottsdale. The most common build — a 600 sq ft detached mid-range casita in Phoenix — costs $160,000 to $220,000. Scottsdale runs 20–30% higher than the Phoenix average. Tucson is 20–25% less. Caliche soil can add $5,000–$20,000 to site prep on lots with heavy calcium carbonate deposits.

Arizona House Bill 2720, signed May 2024 and effective January 2025, requires all Arizona cities with populations over 75,000 to permit ADUs (casitas) by right on single-family lots. Cities can no longer require special use permits, public hearings, or variances for standard ADU applications. HB 2928, signed May 2025 and effective January 2026, extended the same requirements to all unincorporated county areas statewide.

Yes — and this is the most important fact for Arizona homeowners. Both HB 2720 and HB 2928 explicitly preserve the enforceability of private HOA CC&Rs. If your association's covenants prohibit ADUs, detached structures, or additional dwellings, your HOA can deny the project regardless of what state law says. Always obtain a copy of your CC&Rs and submit a pre-application to your HOA Architectural Review Committee before spending money on plans. This is the number one source of stopped Arizona ADU projects.

Caliche is a hardened layer of calcium carbonate that occurs naturally throughout Arizona's desert soils. It can be 6 inches to several feet thick and behaves like concrete when encountered during excavation. Breaking caliche for ADU foundations and utility trenching (water, sewer, electrical conduit) adds $5,000–$20,000 to site preparation costs depending on depth and prevalence. Caliche risk varies block by block — lots with prior landscaping are often pre-broken. Get a soil test before signing a fixed-price construction contract.

A mid-range 600 sq ft casita in Phoenix costs $165,000 to $220,000 all-in and generates $1,600 to $2,200 per month in long-term rental income. Cash-on-cash ROI runs 7–10%, with a payback period of 9–12 years on a cash-funded project. Scottsdale commands higher rents ($2,000–$2,800) but higher construction costs — ROI is similar. Short-term rental income in Phoenix premium markets can reach $3,000–$6,000 per month but requires owner-occupancy of the primary home.

Arizona's building code requires ADUs to meet residential HVAC standards — but the desert environment means spec matters far more than in other states. Phoenix and Tucson regularly exceed 115°F in summer. A mini-split system sized for desert conditions (typically 1.5–2.5 tons for 500–800 sq ft) runs $6,000–$14,000 installed — significantly more than comparable builds in milder climates. Budget for high-efficiency systems; undersized HVAC is the most common post-occupancy ADU complaint in Arizona.