Start with the size you're allowed
Inside the City of Tucson, Arizona's HB 2720 means a casita (ADU) can be up to 75% of the main home's floor area or 1,000 sq ft, whichever is smaller. Here's how that works out:
- 1,000 sq ft home: up to 750 sq ft.
- 1,200 sq ft home: up to 900 sq ft.
- 1,334 sq ft home or larger: the 1,000 sq ft cap applies.
That's the ceiling, not a target. Setbacks, lot coverage and height from the city's zoning code decide what actually fits on your lot. In unincorporated Pima County, a detached casita is a guest house and its coverage follows the accessory building standards for your zone. Oro Valley, Marana and Sahuarita set their own limits. Our casita rules guide explains who issues your permit.
Studio casita
One open room for living and sleeping, plus a bathroom and a kitchenette or full kitchen. Studios are the smallest, simplest and usually least expensive layout to build, and they suit a single occupant, a guest suite or a home office with a bathroom.
- Put the bathroom and kitchen on one shared plumbing wall.
- Use a higher ceiling or a clerestory window to make a small room feel bigger.
- Plan where the bed goes before placing windows and the mini-split.
One-bedroom casita
A separate bedroom with a door changes how a casita lives, especially for a parent or a long-term tenant. The usual plan is living room and kitchen at the front, bedroom and bathroom at the back.
- A split layout puts the bathroom between the bedroom and the living area for sound privacy.
- A pocket or barn door saves swing space in tight rooms.
- A covered porch on the west or south side shades the walls from afternoon sun.
One example from the city's library is the Detached Sonoran ADU, a 650 sq ft backyard casita design (KGUN 9).
Two-bedroom casita
Two bedrooms suit a family member with a caregiver, a couple who needs an office, or a rental. Two bedrooms and a bathroom push a plan toward the 1,000 sq ft cap, so they need a main home large enough for the 75% rule to allow it.
- One shared bathroom between bedrooms saves the most space and plumbing.
- Keep hallways short. Every foot of hall is a foot not used for living.
- Check that a two-bedroom plan still fits your setbacks and coverage before falling in love with it.
Layout choices that matter in Tucson
- Orientation. Fewer, smaller windows on the west wall, more glass to the north, and shade on the south.
- Roof. New ADUs in the City of Tucson need a cool roof, and the roof shape also drives cost. A single roofline is the most efficient.
- Utilities. Placing the casita close to your sewer line and electric panel keeps trenching down.
- Accessibility. A step-free entry and a curbless shower make a plan work for every age. See mother-in-law suites.
- Attached or detached. An attached plan saves a wall and some utility work. Compare in our casita vs home addition guide.
The City of Tucson's pre-approved plan library
The City of Tucson selected nine pre-approved casita designs for its Casita Model Plan Library in late 2024. The building plans are already reviewed, and you buy a plan from its designer. You still need a site plan for your own lot, because zoning and utility location are site-specific, plus a permit and a licensed contractor to build it.
A library plan can save design time if one fits your lot and needs. Custom drawings make more sense for an attached unit, an unusual lot, a garage conversion (see garage conversions) or a plan that has to match an existing house closely. We build from either.
Turning a plan into a price
A floor plan only becomes a real number once it's placed on your lot: how far the utilities run, what the ground is like, and how the casita meets the setbacks. Bring the plan you like, or just a rough idea, to a site walk. We check it against your lot, utilities and jurisdiction, then give you a written estimate. Our casita cost guide covers what moves the price, and the ADU builder page covers how we build.