Phoenix ADU Laws: A Guide to the New 'Casita Bill'

The dream of adding a small, stylish home to your Phoenix backyard—whether for family, extra income, or a private retreat—just got a whole lot easier. For years, navigating the maze of local zoning rules made building a "casita" or accessory dwelling unit (ADU) a challenge. But a groundbreaking new state law has completely changed the game for homeowners across the Valley.

If you've been wondering about the new Phoenix ADU laws, you're in the right place. This guide will walk you through Arizona's "Casita Bill," what it means for your property, and the practical steps to building your own beautiful backyard tiny home in Phoenix.

What is Arizona's New 'Casita Bill' (HB 2720)?

Let's start with the big news. In 2024, Arizona passed House Bill 2720, widely known as the "Casita Bill." This landmark legislation, effective January 1, 2025, requires all Arizona cities with populations over 75,000—including Phoenix—to permit Accessory Dwelling Units on single-family lots.

In simple terms, HB 2720 Arizona is a state law that overrides local restrictions that previously made it difficult or impossible to build a backyard cottage. The goal is to address Arizona's housing shortage by encouraging the creation of smaller, more affordable housing options within existing neighborhoods. It empowers homeowners to make the most of their property, whether that means housing an aging parent, giving an adult child a place to start, or generating rental income.

This isn't just a minor tweak to the rules; it's a fundamental shift that puts the power back into the hands of property owners. The law sets clear, reasonable standards that cities must follow, removing many of the biggest roadblocks that stood in the way of ADU construction.

How HB 2720 Changes the Rules for Phoenix Homeowners

So, what exactly does the Arizona Casita Bill change for you? It systematically dismantles the most common barriers that homeowners used to face. Here’s a breakdown of the key protections the new law provides:

• No Owner-Occupancy Required: Previously, some cities required the property owner to live in either the main house or the ADU. HB 2720 prohibits this, giving you the flexibility to rent out both units if you choose.
• Parking Requirements are Gone: One of the biggest hurdles was the need to add extra off-street parking for an ADU. The new law forbids cities from requiring any additional parking for your casita.
• Design Freedom: You no longer have to worry about matching the exact roof pitch, paint color, or exterior materials of your primary home. While your ADU must still meet building codes, you have much more freedom in its design.
• Rental-Friendly: The law explicitly protects your right to rent your ADU as a long-term rental, securing it as a viable investment.
• Reasonable Setbacks: Excessive setback rules often made ADUs impossible on smaller lots. Now, the maximum a city can require for a rear or side setback is just five feet, opening up possibilities for many more properties.

These changes make building an accessory dwelling unit in Phoenix a more straightforward and predictable process. It's a clear signal from the state that these small homes are a welcome part of Arizona's housing future.

Tiny Home on Foundation vs. Wheels: The Critical Legal Difference

When planning your backyard tiny home in Phoenix, it's crucial to understand a key legal distinction: is it on a foundation or on wheels?

Tiny Homes on a Foundation (ADUs)

A tiny home built on a permanent foundation (like a concrete slab) is legally considered an Accessory Dwelling Unit (ADU). This is the type of structure that HB 2720 addresses. These homes are built to the International Residential Code (IRC), ensuring they meet the same safety and quality standards as a traditional home. They become a permanent part of your property, add to its real estate value, and can be legally used as a full-time residence.

Tiny Homes on Wheels (THOWs)

A tiny home on wheels (THOW) or a Park Model is legally classified as a Recreational Vehicle (RV). Because it’s considered a vehicle, you generally cannot live in one full-time in a residential backyard in Phoenix. The rules for RVs are much more restrictive and are not covered by the new Casita Bill.

If your heart is set on a mobile lifestyle, your best option is typically a dedicated community. The Phoenix area has a wonderful variety of parks and resorts designed for this purpose. We cover these in-depth in our guide to Phoenix tiny home communities for 55+ and snowbirds, which are perfect for those who value flexibility and resort-style amenities.

For more information about building a permanent ADU on your property, our team in Phoenix is your go-to resource for navigating the process from design to completion.

A Simple Guide to Phoenix ADU Size and Setback Rules

While HB 2720 sets the statewide minimums, the City of Phoenix has its own specific rules for size and placement. Fortunately, they are clear and designed to encourage development. According to the official City of Phoenix ADU guidelines, here’s what you need to know:

ADU Size Limits

The maximum size of your ADU depends on the size of your lot:

• For lots up to 10,000 sq. ft.: Your ADU can be up to 1,000 square feet, but it cannot be larger than 75% of the main house's floor area. For example, if your main house is 1,200 sq. ft., your ADU can be a maximum of 900 sq. ft. (75% of 1,200).
• For lots over 10,000 sq. ft.: The maximum size increases significantly, but the 75% rule still applies. You can build up to 3,000 square feet or 10% of the lot area, whichever is less.

Setbacks and Placement

• Placement: A detached ADU must be located in the backyard, behind the primary home.
• Setbacks: Your ADU must be at least 3 feet from the side and rear property lines. If it's next to a public street, the setback is 5 feet. If your property backs up to an alley, you may even be able to build with a 0-foot setback.
• Height: The maximum height for an ADU is typically 15 feet.

These generous rules provide plenty of flexibility to design a comfortable and functional living space that fits perfectly on your property.

The Permitting Process: What to Expect in Phoenix

With the new laws in place, the permitting process in Phoenix is more of a clear checklist than a confusing ordeal. Here’s a simplified overview of the journey:

1. Design and Plans: The first step is to create a set of architectural plans that meet city building codes (IRC Appendix Q for tiny homes) and the zoning rules we just covered.
2. Submit Your Application: You'll submit your plans to the Phoenix Planning and Development Department. The application will be reviewed to ensure it complies with all regulations.
3. Review and Approval: The city's review process typically takes 8 to 12 weeks. They will check your plans for structural safety, utility connections, and zoning compliance.
4. Permit Issuance: Once your plans are approved, you'll be issued a building permit, and construction can begin!

It's important to budget for the associated costs. Permitting fees in Phoenix typically range from $1,000 to $2,500, but this is just one piece of the financial puzzle. For a complete picture of the investment, from site prep to finishing touches, be sure to read our detailed guide on the cost of a tiny home in Phoenix.

Next Steps: Planning Your Phoenix Backyard Tiny Home

The new Phoenix ADU laws have opened a door for thousands of homeowners. The "Casita Bill" provides a clear, legal path to adding a beautiful, functional tiny home to your property, boosting its value and utility.

Feeling inspired? Here's how to get started:

• Evaluate Your Property: Take a look at your backyard. Do you have the space to accommodate an ADU while respecting setbacks?
• Define Your Goal: Are you building for a family member, as a rental unit for extra income, or as a private office or studio? Your goal will shape the design.
• Consult the Experts: Building an ADU is a significant project. Partnering with a team that understands the local codes, design possibilities, and construction process is key to success.

At Clever Tiny Homes, we specialize in navigating these exact projects. We're passionate about helping Phoenix residents unlock the potential of their property. To learn more about our models and how we can help you build the backyard home of your dreams, visit our Phoenix location page and connect with our team today.