Zoning & Size Limits
| Requirement | Denver, CO | Phoenix, AZ |
|---|
| Allowed Zones | All zones that allow a single-family dwelling (citywide as o | Single-family residential zones |
| Max Size (Detached) | Up to 1,000 sq ft on lots over 7,000 sq ft (864 sq ft on 6,000-7,000 sq ft lots; ~650 sq ft on smaller lots) — varies by zone district | 1,000 sq ft on lots up to 10,000 sq ft (75% of primary dwelling, whichever is less); on lots over 10,000 sq ft, the lesser of 3,000 sq ft or 10% of net lot area |
| Max Size (Attached) | Up to 1,000 sq ft (varies by zone district) | 75% of primary dwelling, capped at 1,000 sq ft (lots ≤10,000 sq ft) |
| Max Height | 24 ft / 1.5 stories maximum | 15 ft when within required rear/side yards (greate |
| Parking Required | Not required (no parking minimum for ADUs per HB24-1152 / CB | No additional parking required (ARS 9-461.18 / AZ HB 2720 pr |
| Owner Occupancy | Not required (removed by CB24-1303, effective Dec 16, 2024; | Not required for long-term rental; owner must reside on-site |
Setback Requirements
| Setback | Denver, CO | Phoenix, AZ |
|---|
| Rear Setback | Must be within rear 35% of lot; 5 ft minimum rear setback | 5 feet (3 ft for some detached configurations per ZO 706; statute caps rear/side at 5 ft) |
| Side Setback | Varies by lot width (typically 3-5 ft); confirm with Denver CPD | 5 feet (3 ft for some detached configurations per ZO 706) |
| Front Setback | Matches the primary structure front setback (varie | Per underlying zoning district (no ADU-specific fr |
Permits & Timeline
| Detail | Denver, CO | Phoenix, AZ |
|---|
| Permit Timeline | 4-7 months realistic from application to issued permit (zoning + building review) | 60-90 days |
| Permit Fees | $500-$5,000 building permit + ~$2,055 Denver Water SDC (rising to $2,170 on Jul 1, 2026); total permit/utility typically $6K-$10K | $2,500-$4,200 |
| Impact Fees | Denver Water system development charge applies; see fees | $900-$1,600 |
| Pre-Approved Plans | Pre-approved/standard plan options available | Limited availability |
Construction Costs
| Cost | Denver, CO | Phoenix, AZ |
|---|
| Avg Build Cost | $140,000-$280,000 | $120,000-$240,000 |
| Cost Per Sq Ft | $130-$260 | $135-$270 |
| Garage Conversion | $70,000-$160,000 | $60,000-$140,000 |
| Prefab ADU | $100,000-$230,000 | $85,000-$200,000 |
Rental Income Potential
| Rental | Denver, CO | Phoenix, AZ |
|---|
| 1BR Avg Rent | $1,400-$1,900/mo | $1,250-$1,700/mo |
| 2BR Avg Rent | $1,800-$2,500/mo | $1,600-$2,200/mo |
| Short-Term Rentals | Yes, with STR license | Varies by neighborhood |
| Est. ROI | 7-9% annual return | 7-10% annual return |
Which City Is Better for ADUs?
Denver scores 8/10 while Phoenix scores 6/10 on our ADU-friendliness index.
Denver edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
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