ADUs (Accessory Dwelling Units) Model Plans Pilot Program
 

Through the ADU (Accessory Dwelling Unit) Model Plans Pilot Program, the Flagstaff Sustainability Division, in partnership with the Housing, Planning, and Building Safety sections in Community Development, seeks to increase the number of ADUs in Flagstaff by reducing barriers to ADU construction. This program will:

1. Create an online ADU Model Plans Library to host a growing inventory of pre-approved all-electric and energy-efficient ADU model plans;
2. Simplify the process and reduce the time and costs to design and permit ADUs;
3. Connect interested homeowners with design professionals and other ADU resources; and
4. Increase awareness of ADUs and their benefits to the Flagstaff community.

Staff will discuss the proposed program as well as background research findings.

ADUs are an excellent example of alignment among sustainability and housing goals. The City’s Carbon Neutrality Plan and the 10-Year Housing Plan adopted by City Council in 2021 and 2022 both include strategies to increase the supply of ADUs.  ADUs are smaller, more affordable housing units in existing neighborhoods with access to existing infrastructure and transportation networks. ADUs provide supplemental income, opportunities to downsize, and the opportunity for enhanced social connections. ADUs also offer lower utility bills due to their small size and provide an excellent opportunity to grow the stock of all-electric, energy-efficient housing in Flagstaff.

Staff started the ADU Model Plans Pilot Program development process by conducting research to better understand the most effective way to increase the supply of ADUs in Flagstaff during this initial pilot project. Specifically, research focused on Flagstaff residents’ interests in living in ADUs, barriers to designing and building ADUs, what the City can do to make it easier to build an ADU, how the City can incentivize renting ADUs as long-term rentals, and learning from other cities with model plans libraries. This research was extensive and is described in detail in the ‘Research Findings’ section below.

Most importantly, this research identified several major barriers to ADU construction in Flagstaff, including: 1) construction costs, 2) city design standards, 3) design costs, 4) difficulties finding a designer, 5) navigating the City design and permitting process, and 6) City permitting fees. Based on these findings, staff determined that an ADU model plans library is the most effective way to address the largest number of barriers at this time. Staff will continue to explore other funding and programmatic options to further reduce barriers to ADU construction and increase the deployment of ADUs across the entire Flagstaff community.

Request for Informal Proposals (RFIP)

The City will invite design and construction professionals to submit design concepts for detached ADU model plans through an RFIP in late 2024. Winning designs will be displayed in an ADU model plans library on the City of Flagstaff website. The library will seek to make building an ADU more accessible to Flagstaff homeowners by reducing the time and costs to design an ADU and receive building permit approval.

The RFIP will focus on detached ADUs because it is most feasible to develop model plans for standalone structures. The RFIP will include specific criteria that all designs must meet, which staff anticipate will include:

• Compliance with the 2024 International Energy Conservation Code (IECC)
• All-electric construction (appliances and space/water conditioning must be all-electric)
• The primary heat source must be a cold-climate heat pump (down to -22 degrees) selected from the Flagstaff Sustainability Division’s rebate program list
• Solar-ready construction, including designing where solar panels would go
• A full kitchen (sink, refrigerator, and permanent cooking appliance) 
• Bathroom (sink, toilet, shower optional bathtub)
• Other required features to be determined

Applicants will be encouraged to submit innovative and creative designs that meet the Flagstaff community’s diverse housing needs, offer lower construction costs, and incorporate additional energy and water efficiency to offer long-term utility savings for ADU occupants. The model plans may also allow for pre-approved customization options, which may provide the option to offer different iterations of the same plan (such as a studio, 1-, and 2-bedroom version). Exact parameters for customization will be finalized in consultation with the Building Safety section and other internal and external partners.

The City will build the pre-approved ADU model plans library in partnership with the Flagstaff community. The program is designed based on feedback from City partners, the Flagstaff community, and design and construction professionals. City staff is in the process of forming a model plan selection committee, which will be comprised of City staff and external partners, including representatives from the City’s Housing, Sustainability, and Planning and Zoning Commissions, and other design and construction professionals. Staff has presented to the City Commissions listed above in addition to the Sustainability Division’s Equity Climate Advisory Committee.

The selection committee will advise on design and selection criteria, and will ultimately select up to (10) winning designs. Winning designers will receive a monetary award. After the winning designs are selected, staff will conduct a community outreach and engagement campaign with support from community partners to raise awareness of the ADU model plans library. Staff plans to create an opportunity for the public to use social media to vote on their favorite design (a ‘People’s Choice Award’) and that the winning design will receive an additional monetary award.

Concurrently, winning designers will be invited to submit full construction plans for building permit review. Staff will review the construction plans for compliance with building code and RFIP design criteria. Winners will receive the monetary award upon building plan approval. This project will also pay building plan review fees to the City’s Building Safety section for winning designs to be certified as pre-approved model construction plans. A preview will be displayed in the online ADU model plans library once the plans are approved.

The designer will retain ownership of their plans and be allowed to charge a reasonable re-use or plan licensing fee for the public to use all plans displayed in the library. Staff anticipates the re-use or licensing fee will be capped, which may be tied to the number of bedrooms (such as a lower maximum fee for a studio and a higher maximum fee for a two-bedroom, for example). The fee will cover the designer’s work with the client to fit and orient the design on the client’s lot (and make sure the design works in the lot) and to navigate the building permit review and approval process. The capped re-use fees will apply to the model plans in the library only and will not apply to the plans if changes require them to be reviewed as custom plans. The maximum re-use or licensing fees for model plans will be determined prior to the issuance of the RFIP.

Once the model plans library goes live, Flagstaff community members will be able to preview the plans. The building permit review process to use the ADU model plans will be designed to be shorter, less expensive, and easier to navigate than a custom plans review for the following reasons:

• Lower and more predictable design costs
• Lower building permit review fees and a shorter building permit review timeline
• Easier for the public to find a designer

The model plans in the library will be reviewed periodically for compliance with adopted codes and required design criteria for inclusion in the library; plans will be required to recertify as model plans as needed. City staff will also continue to build the ADU model plans library into a hub of helpful ADU information for the Flagstaff community, and grow the inventory of model plans either through future RFIPs or by opening up the library to any plans that meet required design criteria and can receive model plan approval.

Background Research

As discussed previously, the ADU Model Plans Pilot Program is being designed based on research and feedback from the Flagstaff community and design and construction professionals. Key findings related to ADU model plans are summarized below. This research included:

1. A community survey on the Flagstaff Community Forum from September – October 2023. The survey received 357 responses. A summary of results from a Flagstaff Community Forum survey is also included as an attachment.
2. A targeted survey to Flagstaff design and construction professionals. The survey received 17 responses providing valuable feedback from local practitioners.
3. Eight in-depth interviews with Flagstaff design and construction professionals.
4. Online research on municipalities with existing and new ADU and model plans programs, including Tucson, Phoenix, and Yavapai County, AZ, Denver, CO, Los Angeles, CA, Eugene, OR, and others. This process also included interviews with staff from some of these organizations.

Key findings about ADU preferences, cost, and rationale:

• The most common reason people build an ADU is to earn additional rental income.
• More than two-thirds of ADU owners stated that rental income from their ADU helps them pay monthly homeownership costs, although they also use their ADUs to house extended family, as well as offer a place for guests to stay.
• Many owners built their ADUs to increase the housing supply in Flagstaff to help address Flagstaff’s housing crisis.
• The survey also asked how much owners spent on their ADU; results ranged from $50,000 to $300,000.
• Almost 50% of single-family homeowner survey respondents without an ADU are interested in building one, but only 14% are likely to build one in the next 1-3 years. 68% of homeowners without an ADU would prefer to build a detached ADU.
• More than 50% of homeowners without an ADU said model plans would make it easier for them to build an ADU.
• Renters also prefer a detached ADU. The most common reasons for wanting to live in an ADU are an opportunity for cheaper rent, to live in a neighborhood they otherwise couldn’t afford and/or is closer to downtown, NAU, or their place of work, and having a sense of community and companionship.

Key findings about barriers to building an ADU:

The cost of ADU construction was identified as the highest barrier to constructing an ADU by a large margin. Although construction costs are generally outside of the city’s control, an ADU model plans library can help alleviate several of the other barriers identified in the survey. Common barriers are presented below:

• Barriers an ADU model plans library can help alleviate
  • Design costs
  • Finding someone to design an ADU
  • Navigating the city design and permitting process
  • City permitting fees
• *Barriers related to City Code
  • Design standards, such as setbacks, height, ADU size, and trees and slopes
• Other barriers
  • Construction costs
  • Financing
  • Navigating the construction process
  • Homeowners’ Association (HOA) standards that restrict ADUs
  • Supply chain issues
  • Utility connections and access issues
  • Neighborhood opposition to ADUs

*Arizona House Bill 2720 now requires all municipalities with a population of more than 75,000 people to comply with state ADU regulations. Proposed Zoning Code updates to comply with state legislation were brought to City Council in October 2024.

Key feedback from design professionals:

The design and construction professional survey respondents and interviewee were generally supportive of the city developing an ADU model plans library and had the following feedback:

• The plan designer should retain ownership of their plans and be able to charge a reasonable fee for the use of their plans. This process will allow the designer to work with the client to ensure the chosen ADU will fit on the site and is properly oriented. It will also allow for customizations and will help the client navigate the city review and permitting process.
• ADUs are a great candidate for all-electric and energy-efficient construction because construction costs are lower with no new natural gas infrastructure and it is easier to design an ADU without natural gas (building code requires more separation of natural gas-powered utilities, which can be difficult in a small space; for example, a gas water heater cannot be next to a bedroom).
• It will be a good idea to provide pre-approved customization options in the plans, and clearly delineate what changes require the plans to be reviewed as custom plans. Having pre-approved customization options for each plan set will increase the variety of plans available in the plans library and will ideally minimize the number of customizations the designer would need to make to pre-approved plans. 
• There will need to be a process to ensure a chosen ADU makes sense on someone’s lot because each lot is unique (slope, aspect, access, shade, etc.).
• There should be opportunities for designers to submit model plans to the library in the future if they’re not able to submit plans in response to the initial RFIP.

 
Model Plans Libraries in Other Cities

ADU model plans libraries are growing in popularity as one of many tools cities can employ to increase housing supply and housing diversity. These libraries are intended to make it easier and cheaper for the public to build an ADU while also benefiting the designers who create the ADU model plans. Further, libraries can be designed according to the unique needs of each community; no two libraries are exactly the same.

Several cities and counties in Arizona and across the U.S. have model plans libraries, including ADU model plans libraries. These programs are in various stages of development; some programs were created several years ago while the City of Tucson held a design contest in early 2024, and the City of Phoenix in partnership with the American Institute of Architects (AIA) Phoenix Metro is currently holding a contest. Links are provided below to several model plans libraries.

1. City of Tucson: ADUs in Tucson (tucsonaz.gov)
2. City of Phoenix:
   1. AIA PHOENIX METRO (aia-phoenixmetro.org)
   2. www.phoenix.gov/homeplans
3. Yavapai County: A Home of My Own! Program - Yavapai, AZ (yavapaiaz.gov)
4. City of Los Angeles ADU Accelerator Program
   1. Model Plans library: https://ladbs.org/adu/standard-plan-program/approved-standard-plans
   2. FAQs about standard plans: https://ladbs.org/adu/adu-faqs
5. West Denver Single Family Plus (WDSF+) ADU Pilot Program: https://www.mywdrc.org/adu-pilot-program
6. Eugene, Oregon Pre-Approved Accessory Dwelling Unit (ADU) Plans Program: https://www.eugene-or.gov/4707/Pre-Approved-ADU-Plans
7. Napa, CA: Napa Sonoma ADU
   1. https://napasonomaadu.org/
   2. https://plans.napasonomaadu.org/