"Casita" is a local word, not a legal category. What matters is whether the city approves your building as an accessory dwelling unit or as a guest house. An ADU can be rented out on its own; a guest house usually cannot. We design and permit both.
How does Scottsdale tell them apart?
Scottsdale publishes the clearest comparison we have found. As of October 2026, its ADU page says:
- A guest house cannot be rented separately from the main residence; an ADU can.
- A guest house shares utilities with the main home; an ADU must be separately metered.
- Guest houses are capped at 50% of the main residence in total; an ADU at 75% of the main home or 1,000 sq ft, whichever is less.
- An existing guest house can become an ADU if it meets the ADU standards and the city approves it.
What about Phoenix?
Phoenix describes an ADU as a separate, self-contained living area, attached or detached, that typically has a kitchen, bathroom, living area and sleeping space. If you want the right to lease the unit, permit it as an ADU from the start. Converting later means a new review.
And Paradise Valley?
Paradise Valley has well under 75,000 residents, so the 2024 state ADU mandate does not reach it. Guest houses there follow the town's own zoning rules on large residential lots. See ADUs and guest houses in Paradise Valley.
Which should you build?
It depends on how the space will be used over the next ten years, not just the next one:
- Visiting family and friends only: a guest house can be simpler, with shared utilities.
- A tenant now or later: build to ADU standards so the lease is legal.
- A parent who may need care: an ADU keeps your options open if a caregiver or renter follows.
- Resale: a buyer may value the flexibility of a permitted ADU. See ADU rent in Phoenix.
Arizona law also bars a city from requiring any family, marital or employment relationship between the owner and the person living in an ADU.