The City of Tempe just made building a new guesthouse or casita a whole lot simpler.
Tempe recently wrapped up its first Accessory Dwelling Unit Design Challenge — a competition to select 10 stylish, affordable and sustainable ADU designs that homeowners will soon be able to build using fast-tracked, pre-approved plans.
With new state legislation requiring cities to allow ADUs on single-family lots, Tempe knew demand was coming.
“Accessory dwelling units were a really common question we were getting,” said Jacob Payne, the city’s principal planner. “We knew there would be a lot of interest in constructing these.”
Strong Community Support
Inspired by similar competitions in Tucson and Phoenix, Tempe launched its own design challenge with a boost from a $20,000 AARP Community Challenge grant. Most of the grant went to prize money for winning architects, along with marketing and outreach to ensure a strong community response.
The competition drew 23 submissions from Arizona as well as California and New York. Tempe aimed for a diverse mix of designs, offering categories for accessible, low-cost, sustainable, and small-footprint ADUs.
“We advertised with that in mind, making sure the designs were versatile enough to fit on different sizes of lots,” Payne said.
A jury of architects, ASU faculty and planning professionals evaluated the entries, while nearly 500 residents participated in online voting. That community input shaped the final slate of winners, especially in categories where Tempe homeowners prioritized low-cost options and smaller footprints that could work around existing backyard features like pools.
Thoughtful design was a clear hallmark of the winning plans, which include breezeblock-inspired midcentury aesthetics, efficient use of compact space, passive-cooling strategies, and sustainable materials tailored to Tempe’s climate — qualities Payne says Tempe residents value.
“They’re all really high architectural quality,” he said. “ADUs have very little impact on the streetscape, but they help us build our housing stock.”
Major Cost Savings for Homeowners
The 10 winning plans will now form Tempe’s new Standard Plan Library, giving residents a menu of pre-approved designs to explore.
“People can scroll through the pictures, window-shop the plans, see how big they are, and reach out directly to the architect,” Payne said. “It cuts out a lot of the cost and saves people time. It lets residents start at Step 3 or 4 in the process, instead of Step 1.”
Each plan includes details on size, layout, sustainability features and designer contact information. Homeowners can simply select a plan, purchase a license from the designer — capped at $5,000 and often far less — and submit it for permits.
The cost savings can be significant. A custom 600-square-foot ADU can run up to $40,000 in architectural fees alone. By contrast, Tempe’s standard plans not only slash those costs but also eliminate thousands more in plan-review fees.
ADUs Are One Piece of the Housing Puzzle
Tempe views ADUs as an important piece of its housing strategy — a way to create affordable homes for family members, renters or aging parents with minimal neighborhood impact.
Tempe’s expanded ADU ordinance is already generating momentum. After only four ADUs were built under the city’s previous pilot program, the city has received 73 applications in 2025 alone.
The city will also launch an ADU dashboard tracking applications and construction trends, and plans to expand its Standard Plan Library again next year, opening the door for more designers to contribute.For now, residents can explore the first 10 winning casitas at www.tempe.gov/StandardPlanLibrary and get a jumpstart on building a backyard home of their own.
