» Maricopa County ADU Rules in 2026: What Scottsdale-Area Homeowners Need to Know

Start with the jurisdiction. Before you sketch a casita, price a guest house, or evaluate rental income, confirm whether your property is in unincorporated Maricopa County or inside a city or town.

That distinction controls which zoning ordinance, permitting process, setbacks, utility rules, and rental regulations apply.

This updated guide summarizes the Maricopa County ADU requirements that generally apply in unincorporated areas and explains how the analysis changes in Scottsdale, Phoenix, Cave Creek, and Fountain Hills.

Updated for August 2026. Regulations, interpretations, and municipal procedures can change. Confirm your project with the relevant planning and building department before making design or financial commitments.

The Short Answer

In unincorporated Maricopa County, qualifying single-family lots may generally have:

One attached ADU
One detached ADU
A possible third detached ADU on parcels of one acre or more, subject to the county’s affordable-housing requirements and applicable zoning standards
An ADU size of up to 1,000 square feet or 75% of the primary dwelling’s floor area, whichever is less, for lots under one acre
No discretionary public hearing or variance for an eligible by-right ADU, although site-plan review and permits are still required

“By right” does not mean “without review.” It means an eligible project can be approved through the applicable administrative process instead of requiring a public hearing, variance, conditional-use permit, or special exception.

Building, fire, drainage, flood-control, utility, septic, and public-health requirements still apply.

First, Identify Your Jurisdiction

A Scottsdale mailing address does not necessarily mean the property is governed by the City of Scottsdale. The same issue can arise in Cave Creek, Fountain Hills, and other communities.

Your property may be:

Inside the City of Scottsdale
Inside the City of Phoenix
Inside the Town of Cave Creek
Inside the Town of Fountain Hills
In another incorporated municipality
In unincorporated Maricopa County

Use the property’s legal location, parcel information, and zoning designation: not only the mailing address.

The Maricopa County Assessor’s Office can help confirm parcel information. For county-zoned property, review the Maricopa County Zoning Ordinance and the county’s adopted regulations.

Unincorporated Maricopa County ADU Requirements

The county framework applies to property outside incorporated city or town limits.

One Attached and One Detached ADU

For a lot or parcel where a single-family dwelling is allowed, current county rules allow:

At least one attached ADU
At least one detached ADU

An ADU is a self-contained living unit on the same lot as a larger single-family home. It typically includes sleeping and sanitation facilities and may include kitchen facilities.

A converted guest suite without independent living functions may not qualify as an ADU. Conversely, a structure with a kitchen, bathroom, sleeping area, and separate entrance may be treated as an independent dwelling unit for zoning and building purposes.

Size Limits for Lots Under One Acre

For lots under one acre, each eligible ADU is limited to:

1,000 square feet, or
75% of the primary dwelling’s floor area

The lower number controls.

Examples:

Primary dwelling floor area	75% calculation	Maximum ADU size
1,200 sq. ft.	900 sq. ft.	900 sq. ft.
1,500 sq. ft.	1,125 sq. ft.	1,000 sq. ft.
2,000 sq. ft.	1,500 sq. ft.	1,000 sq. ft.

The ADU must also remain smaller than the main home. Confirm how the county calculates gross floor area for your specific plan.

Possible Third ADU on One-Acre Parcels

A parcel of one acre or more may be eligible for an additional detached ADU.

The third-unit option is not automatic. The project must satisfy the county’s requirements, and at least one ADU may need to be deed-restricted as affordable housing.

A restricted-affordable dwelling unit is generally tied to households earning up to 80% of area median income, through a deed restriction or development agreement. This is a formal legal restriction: not an informal promise to charge lower rent.

Get the affordability language reviewed before recording documents. A deed restriction can affect future leasing, refinancing, resale, and the property’s overall marketability.

What “By Right” Means

The county’s by-right framework is designed to remove discretionary barriers for eligible ADUs.

Generally, an eligible project should not require:

A public hearing
A variance
A conditional-use permit
A special permit
A special exception

The county may still conduct an administrative review to determine whether the site plan complies with applicable regulations.

You should expect requirements involving:

Building permits
Site plans and construction documents
Setbacks and building placement
Lot coverage
Height
Drainage and grading
Fire access
Electrical, plumbing, and mechanical systems
Water and sewer connections
Septic capacity where applicable
Floodplain or sensitive-environmental-area regulations

The county’s official framework is based on A.R.S. § 11-810.01, which addresses county ADU regulations.

Utilities, Septic, and Site Constraints

A property may qualify for an ADU in theory but still have practical limitations.

Before designing, identify:

Existing water service
Sewer availability and capacity
Septic location and tank capacity
Electrical service
Gas service
Public utility easements
Drainage patterns
Floodplain status
Fire-department access
Required driveway or emergency access

If the new unit will not connect to sewer: or if the sewer system lacks capacity: the county may require the septic system to be adequately sized before construction.

An ADU also cannot be built over a current or planned public utility easement without written consent from the relevant utility.

Scottsdale: The 2025 Article Needs Updating

The prior Griffin Realty article stated that Scottsdale did not have a separate ADU ordinance. That statement is now outdated.

The City of Scottsdale’s official ADU page states that the City Council adopted Ordinance 4687 on September 30, 2025, establishing Scottsdale ADU requirements.

Scottsdale’s current published standards include:

One attached and one detached ADU per qualifying single-family property
A possible third detached ADU on a lot of one acre or more when the affordable-housing requirements are met
A first ADU limited to 1,000 square feet or 75% of the primary dwelling, whichever is less
Additional ADUs limited to 500 square feet under the city’s published materials
Detached ADUs generally prohibited in required front and side yards
A five-foot side or rear setback in qualifying rear-yard locations
Ten feet of separation between an ADU and another dwelling structure
Private outdoor living space
Separate exterior access and a unique address
Utility requirements, including separately metered electrical and gas service

Scottsdale also describes a pre-application and administrative-review process before construction-plan review. Review the City’s ADU FAQ and Section 7.900 of the Zoning Ordinance.

Do not apply unincorporated county assumptions to a Scottsdale property.

Phoenix: Review the City’s ADU Materials

Phoenix has its own ADU framework and permitting process.

The City of Phoenix ADU resource describes attached and detached ADUs, current ordinance changes, standard-plan resources, and the city’s zoning and building review process.

Phoenix materials generally address:

Two ADUs on a typical single-family lot
A possible third ADU on qualifying one-acre parcels
Size limits tied to the primary residence and lot area
Rear-yard placement and height standards
No additional parking requirement specifically for an ADU
Building, electrical, plumbing, and safety-code compliance

Phoenix also offers an ADU standard-plan initiative intended to reduce design barriers for some homeowners. Plans still require a site plan and project-specific permitting.

Check the property’s zoning through the City’s mapping tools before assuming an ADU can fit. Lot coverage, easements, access, and existing structures may be more important than the lot’s total square footage.

Cave Creek: Guest House and Accessory Living Rules

Inside the Town of Cave Creek, do not assume the unincorporated Maricopa County rules apply.

The Town’s current residential zoning materials distinguish between a principal residence and accessory living quarters. In certain Desert Rural zoning districts, a detached guest house or accessory living structure may be possible, subject to:

Zoning classification
Minimum lot size
Buildable-area requirements
Setbacks
Height
Native-habitat corridor requirements
Building permits
Septic and utility limitations

Cave Creek’s residential zoning chapter should be reviewed with the Town before planning a project.

The key question is whether the proposed structure will be treated as a guest house, accessory living quarters, or separately rentable ADU. Those categories may not have identical rules.

Fountain Hills: Confirm Current Town Requirements

Fountain Hills also requires a property-specific review.

Older guest-house provisions and current Arizona ADU legislation may not use the same terminology or impose the same conditions. Before relying on a 2025 summary or a prior approval, confirm:

Whether the parcel is inside Town limits
The current zoning designation
Whether the proposed unit qualifies as an ADU
Whether separate long-term rental is permitted
Applicable setbacks, lot coverage, and height limits
Utility and septic requirements
HOA or deed restrictions
The current permit pathway

Start with the Town of Fountain Hills Planning and Zoning resources.

Practical ADU Checklist

Use this sequence before hiring a builder or ordering plans:

Confirm jurisdiction and zoning. Determine whether the property is governed by Maricopa County, Scottsdale, Phoenix, Cave Creek, Fountain Hills, or another municipality.
Review HOA and deed restrictions. State or local zoning approval does not automatically override private restrictions.
Measure the site. Identify setbacks, easements, existing structures, drainage areas, access routes, and available buildable space.
Calculate the size limit. Compare 1,000 square feet with 75% of the primary dwelling’s gross floor area where applicable.
Verify utilities and septic. Confirm capacity, connection requirements, meter requirements, and potential upgrade costs.
Hire qualified design professionals. Use an architect, engineer, designer, surveyor, or contractor familiar with the applicable jurisdiction.
Obtain zoning and building approvals. Secure the required administrative approvals, permits, inspections, and final sign-offs.
Understand occupancy and rental rules. Review long-term rental, short-term rental, licensing, insurance, and occupancy requirements before projecting income.
Document the completed unit. Retain permits, plans, invoices, final inspections, and certificates for future financing or resale.

How an ADU May Affect a Real Estate Decision

An ADU can improve a property’s usability by creating space for family members, guests, a home office, caregivers, or rental occupants. It may also influence marketability and buyer demand.

The effect on value is not automatic.

A buyer may consider:

Construction quality
Privacy and separation
Parking and access
Utility costs
Rental restrictions
Remaining lot coverage
Permits and final approvals
Insurance and maintenance
Compatibility with the primary home
Neighborhood expectations

For sellers, a permitted and well-documented ADU may be easier to explain and market than an unpermitted conversion. For buyers, an existing guest house requires the same level of due diligence as any other material property feature.

Griffin Realty’s Six-Step Buyer Plan and Seven-Step Seller Plan are designed to help clients evaluate the property, understand the numbers, identify risks, and build a strategy before making a significant decision.

Final Takeaway

The most important 2026 rule is simple:

Do not treat Maricopa County, Scottsdale, Phoenix, Cave Creek, and Fountain Hills as one regulatory area.

Unincorporated Maricopa County generally allows one attached and one detached ADU on a qualifying single-family lot, subject to size, site, utility, and building-code requirements. A third unit may be possible on a one-acre-or-larger parcel when the affordable-housing conditions are satisfied.

Inside a city or town, use that jurisdiction’s current ordinance and permitting guidance.

Regulations can change, and online summaries may become outdated. Confirm the requirements with the relevant planning or building department, a qualified design professional, and appropriate legal or tax advisors before construction, leasing, refinancing, or sale.

Grant Van Dyke