In Tempe, which takes more permission to build in a single-family backyard: a second-story studio over a casita, or a fourplex?
Since January 1, 2026, the answer for many lots near downtown runs against intuition. Tempe's Middle Housing Overlay lets a duplex, triplex, fourplex or townhouse project go ahead as a permitted use, with no rezoning application and no use permit. A two-story accessory dwelling unit anywhere in the city has needed a use permit since a December 17, 2025 Board of Adjustment decision. So for a buyer comparing older single-family homes in central Tempe, what a lot can legally become depends on where it sits on the city's map and on how tall the addition is, two things a listing's square footage and bedroom count leave out.
The second story is where the friction shows up
The clearest local example is a single backyard in the Greater Broadmor area. As the Tempe Independent reported in March 2026, its owners asked to build a two-story casita, and the case went from the Development Review Commission to the City Council. Their contractor had designed it with living space only on the ground floor and storage upstairs.
Neighbors from Greater Broadmor and NuVista objected. The same report describes a petition with more than 300 signatures presented to council on September 18, along with an argument that a second story would not fit the single-story character the Alameda Character Plan describes. AZFamily's October 2025 coverage put the planned height at 18 feet and reported that the contractor said the owners were open to lowering it. In the end, the design changed to one story, the application was withdrawn, and on March 5 the council approved the appeal as moot.
That case is why a buyer's plan for a backyard unit should be sized to the one-story rules. Under the ADU code, a lot zoned for single-family use that has a single-family home can add one attached and one detached ADU. On lots under one acre, each ADU is capped at 1,000 square feet or 75% of the main home's habitable floor area, whichever is smaller. Height is limited to what the zoning district allows, typically 30 feet, but two stories now trigger the use permit. The city can't require extra parking or a matching exterior. Arizona's 2025 follow-up law, HB 2928, kept those limits on cities in place.
Inside the one-mile circle, the bigger right is by right
The middle-housing route works under a different logic. Tempe adopted Ordinance O2025.45 on November 6, 2025, and it took effect January 1, 2026. The overlay text applies to legal lots in single-family districts that sit at least partly within one mile of Tempe's central business district. Because partial overlap is enough, a lot that is cut by the boundary line still qualifies.
The Tempe Tribune described the area as roughly north of Broadway Road, east of Priest Drive, west of Eighth Street and south of Curry Road. A strip under the Phoenix Sky Harbor flight path is excluded. The code's exclusion list covers land in the vicinity of public and military airports, along with areas without water or sewer service.
On an eligible parcel, the code allows:
- One duplex, triplex or fourplex, or up to four townhouse units
- The same setbacks and height limits as the underlying single-family zone
- One parking space per unit, a requirement the ADU route doesn't carry
Before adoption, an October 2025 council-meeting summary estimated that about 2,020 single-family lots would be affected. That number counts eligibility, not buildable sites or projects. Nine months after the effective date, we found no reported middle-housing project in Tempe. For now, the right exists on paper, and the parking requirement takes up yard space that a detached ADU would not.
The historic plan won't redraw single-family streets
Many central Tempe homeowners expected the city's historic work to soften the overlay. The Tribune connected the two directly when it reported that the Downtown Historic Core Plan was proposed partly in response to concerns about mandated middle housing.
The September 2026 final draft is now public. The last community meetings are Wednesday, October 21, 2026: a noon session on Zoom and a 6 p.m. session at the Tempe Transportation Center, 200 E. Fifth St., in the Don Cassano Room. Online comments are open through November 1. After that, the plan goes to city commissions and then the City Council.
The draft addresses single-family lots in three passages:
- The plan "does not recommend any changes to the zoning code," and the zoning code "remains the regulatory framework."
- Its focused Historic Core covers clusters near Mill Avenue and Fifth Street plus groupings to the northwest.
- Land south of University Drive is left out on purpose because "single-family neighborhoods fall outside the scope of a commercial historic core."
Put together, adopting the plan would leave the middle-housing rights on residential streets south of University unchanged. Historic review that does apply to single-family homes comes from somewhere else. The zoning code lists separate Historic Overlay Districts, including Borden Homes and Roosevelt Addition, where applications go through Historic Preservation Office or Commission review before standard permitting. Neither the draft plan nor the overlay explains how middle-housing rights and historic-overlay review interact on a specific parcel, so for those districts the Historic Preservation Office is the place to ask.
The two routes are taxed and financed differently
Choosing between an ADU and a duplex also changes the costs. Here is how the two compare under the overlay code and the city's ADU FAQ:
| ADU route | Middle-housing route | |
|---|---|---|
| Where it applies | Lots zoned for single-family use that have a single-family home | Eligible lots inside the one-mile overlay |
| Units added | One attached plus one detached | Up to four units total on the parcel |
| Parking | Can't be required | One space per unit |
| Assessment ratio, per city FAQ | 10%, still single-family use | 16% for duplexes, triplexes and similar |
| Two stories | Use permit since Dec. 17, 2025 | Follows underlying zone height |
According to the city's FAQ, a single-family home with an ADU is still assessed as single-family use, while duplexes, triplexes and similar properties move to the 16% ratio. That describes how the classification works. Any specific property's tax picture belongs with the Maricopa County Assessor and a tax professional.
Construction cost is the other variable. The city's ADU FAQ cites local builders who put a high-quality Tempe ADU at about $180,000 to $260,000. Standard plans may lower that number. Tempe chose ten winning designs in its 2025 AARP ADU Design Challenge, and the city has had to accept standard-plan submittals since July 1, 2026. Designs become available to license only after each designer finishes the standard-plan review.
Rental use has a date-specific rule. If an ADU built on or after December 20, 2024 is licensed as a short-term rental, Tempe requires the owner to live on site. A buyer whose plan depends on short-term rental income needs the ADU's construction date along with the floor plan. Our Scottsdale piece on HOA rental restrictions covers the private-covenant side of short-term rentals.
What to confirm, in order
On a central Tempe home, these checks follow the same order as the rules above:
- Overlay status. Find out whether the parcel touches the one-mile circle shown in the overlay's boundary figure, and confirm a lot near the edge with city planning staff.
- Historic overlay. Find out whether the lot is in a district such as Borden Homes or Roosevelt Addition, where historic review comes first.
- Covenants. The city says most Tempe subdivisions have no HOA or CC&Rs, but private covenants can be stricter than city rules where they do exist.
- Existing structures. A legal guest quarters counts toward the ADU limit, and a property that already has a duplex can't add ADUs under these rules.
Quick answers
Is the Downtown Historic Core Plan final? No. The September 2026 draft is in its last public comment round, open through November 1, and commission review and council consideration follow.
Can I see how many ADUs Tempe has approved? The city links an ADU statistics dashboard that tracks units in review, under construction and completed. It updates over time, so check it directly.
Does NuVista fall under the middle-housing overlay? Not based on the rough limits the Tribune reported, which stop at Broadway Road. The ADU rules, including the two-story use permit, apply there as they do across the city.
When a Tempe listing's value rests partly on what the lot could hold, it pays to confirm the overlay map, the historic district status and the covenants before you write an offer. Tag Team AZ can help you work through those checks on a specific address and bring in the right city contacts early. For more on the area, see our Tempe neighborhood page, or contact us to talk through a property you're considering.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
