A detached ADU in Phoenix typically runs $150 to $250 per square foot for construction, depending on finishes, site conditions, and whether utilities need to be extended from your main house. An 800 square foot casita usually lands somewhere between $130,000 and $200,000 all in. Bids below $150 per square foot for a fully permitted, detached unit with a kitchen and bath deserve a close look at what is being left out. Attached ADUs or garage conversions generally cost less because you are not starting from a bare slab.

Yes. Arizona passed HB 2720 in 2023, which requires cities including Phoenix to allow ADUs on single-family lots by right. Phoenix allows one ADU per lot. The unit must be a self-contained living space with a kitchen, bathroom, and sleeping area. Setback, height, and lot coverage rules still apply, and the unit must be permitted through the City of Phoenix Planning and Development Department. We pull all permits on every project we build.

Honest answer: upfront cost is the biggest one. You are looking at six figures for a detached build, and financing options are more limited than a standard mortgage. Construction timelines in Phoenix run four to eight months from permit approval for a detached unit, so this is not a fast project. You will also need to account for increased utility costs, potential HOA conflicts if your neighborhood still has rules that predate state law, and the time it takes to manage a rental if that is your goal. None of these are reasons to avoid building one, but they are real considerations.

A room addition attached to your existing home is almost always cheaper per square foot because you share walls and an existing roof. If you need extra space for family, an addition may make more sense. An ADU costs more but gives you a fully independent unit with its own entrance, kitchen, and utilities, which matters if you want rental income, a private space for aging parents, or the ability to sell the property later with a separate living unit on it. The right answer depends on what you actually need the space to do.

Plan on two to four months for design, plan prep, and permit review with the City of Phoenix, sometimes faster if you use a pre-approved floor plan. Construction on a detached ADU typically takes three to five months after permit approval, depending on size and site conditions. From first conversation to move-in, eight to twelve months is a realistic timeline for a ground-up detached casita in the Valley. Garage conversions and attached units can move faster.

The unit must function as a self-contained dwelling, meaning it needs a kitchen with a sink, a bathroom, a living area, and a sleeping space. Only one ADU is allowed per single-family lot. The structure must meet Phoenix building codes, be built on a permitted foundation, and pass inspections. Setbacks, maximum height, and lot coverage limits apply and vary by zoning designation. If you are in an HOA, state law now limits how much an HOA can restrict ADUs, but the rules are still evolving and worth reviewing before you start.

Yes. Phoenix does not prohibit renting an ADU on a single-family lot, and many homeowners build them specifically for rental income. If you plan to use it as a short-term rental, check Phoenix short-term rental ordinances, which require registration and carry specific rules about noise, occupancy, and neighbor notification. Long-term rentals have fewer restrictions. Either way, make sure the unit is fully permitted before you advertise it for rent.