» What Homeowners Need to Know About Building an Accessory Dwelling Unit [ADU] in Maricopa County, Arizona

Accessory Dwelling Units (ADUs) are gaining popularity as homeowners seek ways to maximize their property’s value, create multi-generational housing, or generate rental income. However, zoning laws and building codes vary significantly across different municipalities in Maricopa County, making it essential for homeowners to understand the specific rules in their area.

Whether you’re considering adding an ADU to your property in Phoenix, Scottsdale, Fountain Hills, Cave Creek, or unincorporated Maricopa County, this guide is your comprehensive resource. It will walk you through the latest regulations, requirements, and considerations, ensuring you’re well-prepared for the journey ahead.

What Is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary residential unit on the same lot as a primary home. ADUs can be detached (a separate structure like a guest house or casita), attached (connected to the main house), or converted from existing spaces like garages or basements.

ADUs must have independent living facilities, including a kitchen, bathroom, and separate entrance.

City-Specific ADU Regulations in Maricopa County

City of Phoenix: New ADU Rules in 2024

Phoenix has recently revised its zoning ordinance, empowering homeowners with the flexibility to add up to two ADUs per lot on single-family residential properties. These new rules are designed to increase housing options while preserving the unique character of each neighborhood.

Size Limits:

The total ADU size cannot exceed 75% of the primary residence’s square footage.
Maximum ADU size:
- 1,000 sq. ft. for lots under 10,000 sq. ft.
- 3,000 sq. ft. for larger lots.

Setbacks & Height Restrictions:

Detached ADUs must be at least 3 feet from side and rear property lines and 5 feet from a street-side property line.
Maximum height: 15 feet unless a use permit allows for more.
A detached ADU cannot be placed in front of the primary home.

Design & Appearance:

ADUs must match the main home’s style if visible from the street.
Roofs, siding, and materials should be similar to the primary residence.

Parking:

No additional parking space is required.

For homeowners in Phoenix, this means greater flexibility to add rental units or guest homes without requiring additional permits beyond standard building approvals.

Full Phoenix ADU Guidelines

City of Scottsdale: Accessory Structure Rules

Scottsdale does not have a separate ADU ordinance but allows accessory buildings that can serve as guest houses or rental units.

Size & Placement:

ADUs cannot exceed 25% of the total lot coverage.
Detached ADUs must be behind the main house and not interfere with setbacks.
Minimum 3-foot setback from side and rear property lines.

Occupancy Rules:

Short-term rentals (under 30 days) are heavily restricted.
ADUs cannot be sold separately from the main property.

While Scottsdale’s regulations allow ADUs, they are subject to additional zoning restrictions. Check with the Planning Department to confirm your lot’s eligibility before building.

Full Scottsdale Planning & Zoning Code

Fountain Hills: ADU Approval on a Case-by-Case Basis

Fountain Hills does not have a formal ADU ordinance. However, homeowners can apply for accessory structure permits.

Key Considerations:

Zoning District: Some residential zones allow ADUs, while others do not.
Lot Size Requirements: Larger lots have a better chance of approval.
Architectural Compatibility: ADUs must complement the primary home.
HOA Restrictions: Many communities have HOA rules prohibiting ADUs.

Since Fountain Hills evaluates ADUs on a case-by-case basis, homeowners should consult town planners before investing in construction.

Fountain Hills Planning & Zoning Info

Town of Cave Creek: Limited ADU Opportunities

Cave Creek has more restrictive zoning regulations when it comes to ADUs, but some homeowners may be able to build a guest house if they meet zoning criteria.

Requirements:

ADUs are generally limited to rural residential properties.
Guest houses must be subordinate in size to the primary residence.
Additional septic system upgrades may be required if the system is not connected to the city sewer.

Because Cave Creek has strict land-use regulations, homeowners must verify their lot’s zoning classification before planning an ADU.

Cave Creek Zoning Ordinances

Unincorporated Maricopa County: ADU-Friendly Policies

For homeowners in unincorporated areas, Maricopa County has relatively flexible rules for accessory dwellings.

Zoning & Setbacks:

Detached ADUs must be at least 3 feet from property lines.
Garage conversions & tiny homes may qualify as ADUs if they meet building codes.

Size Limits:

ADUs cannot cover more than 30% of the required rear or side yard.
Height restrictions vary depending on the zoning designation.

Maricopa County’s rules are more lenient than some cities, making it one of the easiest areas to build an ADU.

Full Maricopa County ADU Guidelines

Key Steps for Building an ADU in Maricopa County

Confirm Zoning & Regulations: Check local zoning laws to ensure your property qualifies for an ADU

Secure Permits & Approval: Submit plans to your city’s building department for approval.

Design with Compliance in Mind: Follow setback, height, and design requirements for your jurisdiction.

Address Utility Connections: Plan for water, sewer, and electrical connections to meet city codes.

Comply with Rental & Occupancy Rules: Verify if short-term rentals are allowed or if a minimum lease length applies.

Final Thoughts: Is an ADU Right for You?

Building an ADU can be a significant investment, and it’s important to be aware of the potential challenges. Navigating Arizona’s regulations can be tricky, and the approval process can be time-consuming. Phoenix and Maricopa County are the most ADU-friendly areas, while Scottsdale, Cave Creek, and Fountain Hills have more restrictive policies.

Before moving forward, consult your local planning department to ensure compliance with all zoning, permitting, and design requirements.

By understanding the regulations and planning accordingly, you can create an ADU that enhances your property’s value and functionality.

Grant Van Dyke