If you're thinking about adding a backyard guest house to your Phoenix property, you're not alone. Searches for guest houses in Phoenix have surged over the past year — and for good reason.

Arizona House Bill 2720, passed in 2024, now requires Phoenix and every city in Maricopa County to allow homeowners to build what the city officially calls an Accessory Dwelling Unit or ADU on single-family lots. In plain terms — a detached backyard guest house, casita, or studio is now permitted on most Phoenix metro properties.

What is an ADU and how is it different from
a guest house?

In Phoenix, what most homeowners call a guest house, casita, or backyard cottage is officially permitted and regulated as an Accessory Dwelling Unit. The terms are interchangeable. An ADU is simply the legal name for what most people think of as a guest house — a separate living space on
the same lot as your main home.

How big can my guest house be in Phoenix?

Phoenix uses a two-tier calculation based on your lot size.

If your lot is under 10,000 SF your guest house can be up to the lesser of 1,000 SF or 75% of your main home's square footage.

If your lot is over 10,000 SF your guest house can be up to the lesser of 3,000 SF, 10% of your lot area, or 75% of your main home's square footage.

How close to my property line can a guest
house be built?

A detached guest house in Phoenix must be at least 3 feet from interior side and rear property lines, and at least 5 feet from a street side property line. No setback is required if the structure is adjacent to a fully dedicated alley.

Do I need a permit to build a guest house
in Phoenix?

Yes. All ADU and guest house construction in Phoenix requires a building permit. You will need approved architectural plans, a site plan, and inspections at key stages of construction.

How do I find out exactly what I can build
on my specific property?

Every property is different. Lot size, zoning district, existing structures, and lot coverage all affect what you can build and where. A CasitaReady Assessment gives you a property-specific analysis of your guest house development potential — covering eligibility, maximum size, development standards, lot coverage, permit timeline, and construction costs — delivered within 24 hours for $39.