6.A.
Heritage Preservation Commission
- Meeting Date:
- 02/18/2026
- Co-Submitter:
- Lauren Clementino
- From:
- Genevieve Pearthree, Senior Sustainability Planner
TITLE:
Flagstaff Accessory Dwelling Unit (ADU) Model Plans Library and the Townsite Historic Overlay Zone
STAFF RECOMMENDED ACTION:
Provide direction on which, if any, of the pre-approved plans in the Flagstaff ADU Model Plans Library are likely to comply with the Townsite Design Standards and Guidelines.
Executive Summary:
Purpose of this Presentation
The purpose of this presentation is to provide HPC an opportunity to proactively review the pre-approved ADU model plans in the Flagstaff ADU Model Plans Library prior to reviewing Certificate of Appropriateness requests for these ADUs to be built within the Townsite Historic Overlay Zone. This review will provide HPC with the opportunity to identify which plans, if any, are likely to comply with the Townsite Design Standards and Guidelines. This exercise will also provide Townsite property owners with a useful starting point when selecting from the pre-approved ADU model plans.
City staff have conducted a preliminary review of the 12 pre-approved ADU Model Plans against the Townsite Design Standards and Guidelines for HPC’s review and consideration. Staff have compiled characteristics about each plan into a table, which is included in the attachments to this staff summary. Characteristics include: height, roof pitch, square footage, bedroom and bathroom count, and exterior materials.
After receiving HPC direction, staff will prepare a draft memo identifying which ADU model plans are likely to meet the Townsite Design Standards and Guidelines and bring it back to HPC at a future meeting. Townsite property owners will still need a Certificate of Appropriateness from HPC prior to applying for a building permit to build an ADU, which will confirm that the ADU on a specific lot will meet the Townsite Design Standards and Guidelines. However, reviewing the plans now will ideally make the process smoother in the future for both HPC and the property owner.
Overview of ADUs and Purpose of the ADU Model Plans Library
The City launched the Flagstaff Accessory Dwelling Unit (ADU) Model Plans Library in January 2026 at www.flagstaff.az.gov/ADUs. The Library contains 12 pre-approved, publicly viewable ADU model plans, while additional plans are currently under review. The plans were selected through a 2025 Request for Informal Proposals (RFIP), which attracted over 30 design proposals. A selection committee of community partners and City staff selected the 10 winning designs and several runners-up.
ADUs, also known as backyard homes or casitas, are important to the City’s climate and housing goals because these smaller housing units can offer lower rents and monthly utility costs, and increase Flagstaff’s housing supply. These units can also provide more flexible housing options for households of all sizes, generate supplemental rental income for homeowners, and increase housing availability in established neighborhoods.
Model plans are intended to lower the barriers to ADU construction in Flagstaff by reducing the cost to design an ADU, making it easier to find a designer, simplifying the design and permitting process, and providing access to lower City permitting fees for model plans (compared to City fees for custom plans).
To build an ADU using a pre-approved model plan, Flagstaff community members can browse the Library, select their favorite plan, contact the designer to purchase access to the full plans, work with the designer to draft a site plan, and proceed through the City’s building permit review and approval process. Several of the ADUs have pre-approved options, including floor plans, roof plans, foundation types, and exterior materials that community members can choose from.
The plans are “pre-approved” because they have already gone through City of Flagstaff Building Plan review to confirm they comply with the City’s adopted building and fire codes. This means that when a property owner applies to use the plans on an individual lot, the City review is only focused on whether the ADU will meet relevant Zoning and other City design standards on that lot. Ideally, the City review process for pre-approved plans on a particular lot is shorter and less costly than a custom plans review.
The City of Flagstaff Zoning Code allows ADUs to be built on any property that already has a single-family home, including properties in historic districts, provided the ADU meets relevant development code requirements. The Townsite Historic Overlay Zone is the only residential historic overlay zone in Flagstaff with additional design standards that ADUs must comply with beyond the City’s base development code. New construction in the Townsite Historic Overlay Zone requires a Certificate of Appropriateness from the Heritage Preservation Commission prior to applying for a building permit for a property within the Overlay.
The purpose of this presentation is to provide HPC an opportunity to proactively review the pre-approved ADU model plans in the Flagstaff ADU Model Plans Library prior to reviewing Certificate of Appropriateness requests for these ADUs to be built within the Townsite Historic Overlay Zone. This review will provide HPC with the opportunity to identify which plans, if any, are likely to comply with the Townsite Design Standards and Guidelines. This exercise will also provide Townsite property owners with a useful starting point when selecting from the pre-approved ADU model plans.
City staff have conducted a preliminary review of the 12 pre-approved ADU Model Plans against the Townsite Design Standards and Guidelines for HPC’s review and consideration. Staff have compiled characteristics about each plan into a table, which is included in the attachments to this staff summary. Characteristics include: height, roof pitch, square footage, bedroom and bathroom count, and exterior materials.
After receiving HPC direction, staff will prepare a draft memo identifying which ADU model plans are likely to meet the Townsite Design Standards and Guidelines and bring it back to HPC at a future meeting. Townsite property owners will still need a Certificate of Appropriateness from HPC prior to applying for a building permit to build an ADU, which will confirm that the ADU on a specific lot will meet the Townsite Design Standards and Guidelines. However, reviewing the plans now will ideally make the process smoother in the future for both HPC and the property owner.
Overview of ADUs and Purpose of the ADU Model Plans Library
The City launched the Flagstaff Accessory Dwelling Unit (ADU) Model Plans Library in January 2026 at www.flagstaff.az.gov/ADUs. The Library contains 12 pre-approved, publicly viewable ADU model plans, while additional plans are currently under review. The plans were selected through a 2025 Request for Informal Proposals (RFIP), which attracted over 30 design proposals. A selection committee of community partners and City staff selected the 10 winning designs and several runners-up.
ADUs, also known as backyard homes or casitas, are important to the City’s climate and housing goals because these smaller housing units can offer lower rents and monthly utility costs, and increase Flagstaff’s housing supply. These units can also provide more flexible housing options for households of all sizes, generate supplemental rental income for homeowners, and increase housing availability in established neighborhoods.
Model plans are intended to lower the barriers to ADU construction in Flagstaff by reducing the cost to design an ADU, making it easier to find a designer, simplifying the design and permitting process, and providing access to lower City permitting fees for model plans (compared to City fees for custom plans).
To build an ADU using a pre-approved model plan, Flagstaff community members can browse the Library, select their favorite plan, contact the designer to purchase access to the full plans, work with the designer to draft a site plan, and proceed through the City’s building permit review and approval process. Several of the ADUs have pre-approved options, including floor plans, roof plans, foundation types, and exterior materials that community members can choose from.
The plans are “pre-approved” because they have already gone through City of Flagstaff Building Plan review to confirm they comply with the City’s adopted building and fire codes. This means that when a property owner applies to use the plans on an individual lot, the City review is only focused on whether the ADU will meet relevant Zoning and other City design standards on that lot. Ideally, the City review process for pre-approved plans on a particular lot is shorter and less costly than a custom plans review.
The City of Flagstaff Zoning Code allows ADUs to be built on any property that already has a single-family home, including properties in historic districts, provided the ADU meets relevant development code requirements. The Townsite Historic Overlay Zone is the only residential historic overlay zone in Flagstaff with additional design standards that ADUs must comply with beyond the City’s base development code. New construction in the Townsite Historic Overlay Zone requires a Certificate of Appropriateness from the Heritage Preservation Commission prior to applying for a building permit for a property within the Overlay.