How is a guest house different from an ADU?
An ADU is a dwelling you can lease on its own. A guest house, as Pima County describes it, is used mainly by the family living in the main home and their nonpaying guests. That one difference changes utilities, rental rights and sometimes size.
What are Pima County's guest house rules?
For unincorporated areas such as the Catalina Foothills, Pima County's guest house page lists, as of October 2026:
- A minimum lot size of 4,000 sq ft.
- One guest house per lot, with at least two rooms and a bathroom; a kitchen is optional.
- No separate utility meters from the main home.
- The same driveway access that serves the main home.
- At least 3 feet from the main residence, with setbacks from the zone's accessory building standards.
- Submittal through the county's custom home process.
Is there a care-related option?
Yes, in the county's RH and GR-1 zones. A secondary dwelling permit allows a unit for an ill, disabled or elderly person who needs care, or for their caregiver. It is limited to one per lot, must use the main home's access, runs for up to three years with renewal, and the unit must be removed within 90 days after the named person leaves.
Which should I build?
It depends on the next decade, not the next visit. If there is any chance you will lease the space, build an ADU. Arizona's 2025 county ADU law, A.R.S. § 11-810.01, requires counties to allow ADUs that can be rented long-term, so an ADU is usually the more flexible choice in Pima County too. Inside Tucson, the city's casita rules already treat the unit as an ADU.
Can I convert a guest house later?
Usually it means a new review and often separate utilities. Designing to ADU standards from the start saves that second round.
Related
As of October 2026, from Pima County's Guest Houses page, Pima County Code § 18.09.020 and A.R.S. § 11-810.01.
Guest house or rentable casita?
Tell us how the space will be used. The permit should fit the use, and we set it up that way.