What is an attached ADU?
A unit that shares a wall with the main house but has its own sleeping area, bathroom and outside door. State law requires Tucson to allow one attached ADU on a single-family lot, alongside one detached ADU.
What rules apply in Tucson?
- The same state minimum for size: at least 75% of the main home or 1,000 sq ft, whichever is less.
- Under Tucson's 2021 rules, an attached ADU could already match the main building's height; the 2024 update revised height limits again.
- No more than 5 feet may be required from side and rear lines.
- No design-matching requirement: Arizona law bars a city from requiring the ADU to copy the house's style, roof pitch or materials.
Why choose attached?
- Shorter plumbing and power runs, since the house is right there.
- More yard left for shade trees, a garden or a pool.
- Close but separate for an aging parent or an adult child.
What makes it harder?
The tie-in. Joining a new roof to an old one is where monsoon leaks start if it is done poorly, so we detail flashing and drainage carefully. The shared wall also needs fire separation under the building code. Arizona law does not let a city require fire sprinklers in an ADU, but the separation rules still apply.
Attached or detached?
It depends on the yard, the budget and how much privacy both households want. Attached is often cheaper per square foot because of utilities; detached gives more distance. We price both if your lot allows either.
Related
As of October 2026, from A.R.S. § 9-461.18, City of Tucson PDSD and KGUN reporting on the 2021 ordinance.
Room to build onto the house?
Send your address and tell us which side of the house you have in mind.