New Build Attached ADU

[Kenneth Stephen Roleke]

I've been building starter homes in Rio Rico, AZ, for the past 4+ years, about 20 miles from the Mexican border at Nogales, selling a few a year, and keeping 1-2 a year as rentals. Arizona now allows one detached and one attached ADU per lot. I am interested in developing a plan for a house with an attached ADU, with the ADU a 2 bedroom, 1 bathroom, about 750 square feet, and the main house 3 bedroom, 2 bathroom, about 1250 square feet, no covered parking. I was looking online for ideas, but the only houses I see with in-law suites are much larger than the 2000 square foot or so building I am aiming for. The ADU can be no more than 75% of the interior habitable area of the main house, and no more than 1000 square feet. Is anyone aware of stock plans similar to what I would like to build?

[Ashish Acharya]

Kenneth, I'd think about the ADU design from three angles at the same time: rentability, construction efficiency, and long-term flexibility.

If the attached ADU is going to be a true rental, I'd want the layout to feel independent even though it shares the structure. Separate entrance, good sound separation, its own laundry if possible, enough kitchen storage, and clear utility metering or allocation can make a big difference in how easy it is to rent and manage.

Since you’re building from the ground up, I’d also keep the construction accounting very detailed. Separate site work, appliances, cabinetry, flooring, electrical, plumbing, HVAC, and other components instead of letting everything disappear into one construction number.

That becomes important on the tax side because once the rental portion is placed in service, cost segregation may accelerate depreciation on qualifying components. But I’d still do a detailed analysis first to make sure the resulting losses are actually usable rather than assuming the depreciation automatically creates immediate tax savings.

I’d also make sure the final plan is reviewed for zoning, setbacks, utilities, parking, fire separation, and whatever local requirements apply before getting too far into architectural work.

The best stock plan is probably the one that keeps the ADU simple to build, easy to rent, and easy to account for separately.

Happy to connect!