Accessory Dwelling Units (ADUs) Code Amendment Frequently Asked Questions

  1. What is the current proposal to allow Accessory Dwelling Units?

The current proposal would allow:

  • One ADU to be built on any residential lot in the city (meaning a lot with one or two homes)
  • The maximum size of the ADU would be 1,000 square feet for lots over 7,000 square feet and 750 square feet on lots under 7,000 square feet
  • All other dimensional standards, including maximum building height, lot coverage, and setbacks would apply
  • One parking space would be required per ADU, which could be waived for sites that are a quarter-mile from transit or a bike boulevard; on-street parking can also be used
  • Each newly constructed ADU would be required to have a cool roof
  1. What is the difference between what is allowed currently and the proposed regulations for Accessory Dwelling Units (ADUs)?
  • There are currently two options to build a unit similar to an Accessory Dwelling Unit – it could be built as sleeping quarters or a second residential unit.
  • Currently, detached sleeping quarters are allowed in all residential zones. These structures function very similarly to an Accessory Dwelling Unit. The key differences are that a full kitchen is not permitted, the maximum area is restricted to 50% of the area of the primary unit, and the building height is restricted to a maximum of 12 feet.
  • Additionally, a second residential unit is allowed on lots above a certain size, based on the zone. For example, in R-1, the most common zone across the city, lots over 10,000 square feet may add a second unit.

The chart below compares the current regulations with the proposal for Accessory Dwelling Units.


Sleeping Quarters - CURRENTLY ALLOWED

Second Residential Unit – CURRENTLY ALLOWED

Accessory Dwelling Unit (ADU) - PROPOSED

What zones are they allowed in?

All residential zones

R-1, R-2, R-3, MH-1, & MH-2 Residential Zones, and all Office and Commercial Zones

All zones that allow for residential uses

What parcels may build one?

Any parcel with a residential dwelling unit

R-1 parcels > 10,000 SF

R-2 parcels > 5,808 SF

R-3 parcels > 5,000 SF

MH-1 parcels > 10,890 SF

MH-2 parcels > 5,808 SF

Office and Commercial must meet density requirements and minimum lot size requirements

Any parcel with single and two-family residential units

Maximum Size of Unit

50% of primary structure

No size restriction – in R-1 one dwelling must be 25% smaller than the other dwelling.

1,000 SF


No parking required beyond requirement for principal use

Parking required per use standards

1 parking space required per ADU; can be waived if 1/4 mile from Transit or a Bike Boulevard

Number of bedrooms

No limit

No limit

No limit

Type of Kitchen

Wet bar setup including single-bowl sink and under-the-counter fridge. No cooking facilities permitted.

Full Kitchen

Full kitchen


Per zone standards

Per zone standards

Per zone standards

Process to reduce setbacks

Written consent of neighbor or Design Development Option

Design Development Option (DDO)

Design Development Option (DDO)

Maximum Building Height

12 feet maximum, unless attached to the principal building

Per zone standards – typically 25 feet maximum

Per zone standards – typically 25 feet maximum

Privacy Mitigation


Per HPZ or NPZ Standards if in those zones. If not, none, but variable setbacks require building to be set back further as the height increases

None, but variable setbacks require building to be set back further as the height increases. NPZ standards apply.

Urban Heat Island Effect (UHI)

No requirement to mitigate urban heat island effect

No requirement to mitigate urban heat island effect

Cool roof required

  1. What is affordable housing and how do ADUs help address housing affordability?
    • Affordable housing is housing a household can pay for, while still having enough money left over for other necessities like food, transportation, and healthcare. The federal government typically defines housing as affordable when it consumes no more than 30% of a household’s income. While all ADUs are not necessarily affordable by HUD standards (70% of Average Median Income (AMI), they help to provide a greater mix of housing types and options. For example:  
      • ADUs are likelier to provide rental housing that is affordable within its neighborhood context than rental housing in general[1].
      • ADUs appear to be likelier to bolster income diversity through addition to the stock of modestly priced rental apartments in high-opportunity neighborhoods than are other types of unsubsidized rental housing.
      • The “supply effect” - Supply and demand play an important role in maintaining affordability – increasing the supply takes pressure off demand and reduces the pricing power of the landlord.
      • Less square footage = lower rent
    • Additionally, to help support affordable ADUs, programs can be set up by the City, such as:
      • Develop pre-approved model plans to be used by homeowners to help reduce costs.
      • Fee waivers in certain circumstances to help reduce costs.
      • Partnerships with local organizations to help provide technical assistance to low- and moderate-income households as well as financial assistance or access to capital.
      • Federal Housing programs to subsidize the rent paid to the landlord.
  2. How do ADU’s help address housing and opportunity equity?
    • ADUs are commonly created in low-density residential neighborhoods where lower-cost housing types might otherwise be unavailable, helping to expand access to resource-rich areas for low- and moderate-income households.
      • For example, resource-rich areas are those that have abundant amenities such as access to quality schools and public libraries, streets, and parks that are free from violence and provide a safe place to play and fresh and healthy food. These are also sometimes called “opportunity areas.”
  3. How do ADUs support multigenerational housing and changing societal preferences? 
    • ADUs allow for seniors, disabled individuals, adult children, etc. to maintain independence through a separate space, while still being close to their family members. Increasingly we are seeing a return to this living situation as housing costs increase, older generations look to downsize, and younger generations prefer to rent at a higher rate and have smaller households than the previous generations.
  4. How do ADUs address sustainability and the City of Tucson’s climate goals?
    • ADUs support infill development and use of existing infrastructure as an alternative to sprawl and development on the periphery. The alternative to infill – sprawl - is detrimental to the environment in that it destroys natural land, disrupts ecosystems, requires additional infrastructure, more pollution, etc. The increased density created by the ADUs helps to support effective public transit, bike use, and pedestrian systems.
    • New construction also must meet current building code and energy code standards, which is much more efficient than standards used for older housing.
  5. What impact will the development of ADUs have on heat generation and the Urban Heat Island (UHI) Effect?
    • Research generally shows that gradually increasing density (e.g ADUs) will not in itself increase the UHI effect for a specific area.
    • Additionally, new development with a light-colored "cool roof” can actually reduce the Urban Heat Island effect when developed on previously barren ground.
    • Research comparing Civano Phase 1, where reflective white roofs were used with other neighborhoods showed that neighborhoods with cool roofs have lower temperatures. 2
    • In order to mitigate the urban heat island effect, this proposal would require that newly constructed Accessory Dwelling Units include a cool roof.
  6. What are ADUs effect on neighborhood stability and housing values?
    • As property values increase, so does the property tax rates – if a homeowner cannot bear the cost of increased property taxes, they may be forced to relocate. The option for a property owner to generate passive income can help support the property owner’s cost of living in that area. Moreover, the option for a property owner to earn additional income can help support their mortgage payments.
    • Adding built improvements only adds value to the property – the owner is investing in their property. This is called a positive externality where the increased value of a neighbor’s property has the same effect on an adjacent neighbor’s property.
  7. Can we require that a property owner reside in the ADU or primary home?
    • This proposal does not regulate the occupancy of an ADU or the primary structure on a lot where an ADU is built.
    • An owner-occupancy requirement can make it difficult to finance an ADU and to sell a property with this requirement
    • If circumstances of the property owner change, this requirement could be a liability
    • Occupancy is not regulated for other homes and is not regulated elsewhere in our zoning code
    • We are seeing changing household preferences – more households are choosing to rent today. Therefore limiting ADUs to lots with a property owner on-site limits who can benefit from this option.
  8. Can we make sure that ADUs are not just used for short-term rentals (Airbnb, VRBO, etc.)?
    • Currently, Arizona law prohibits a city or county from restricting the use of or regulating vacation or short-term rentals based on their classification, use, or occupancy[2].
  9. How are ADUs different from mini-dorms?
    • The current proposal would limit an Accessory Dwelling Unit to a maximum of 1,000 square feet, which is large enough to potentially allow a 2-bedroom unit.
    • Accessory Dwelling Units must comply with group dwelling regulations. These regulations prohibit 5 or more unrelated individuals from residing in a home, or in R-1 zones, on a lot.
  10. Could an ADU be purchased separately from the main home?
    • In order for an ADU to be owned separately from the main structure, the lot would need to be split. The new lots must meet minimum lot size requirements, which are for 7,000 square feet in R-1 and 5,000 square feet in R-2, and R-3, to name a few common residential zones. Once the lot with the ADU was split off, the ADU would no longer be an accessory unit but would be the primary residential structure.
  11. Will this allow tiny homes?
    • “Tiny home” is a term that can be applied to a number of types of homes. Tiny homes are generally defined as a home that is 400 square feet or less. These could qualify as an Accessory Dwelling Unit. It’s important to note that this proposal does not allow tiny homes on wheels, which are considered a vehicle, rather than a dwelling. Accessory Dwelling Units must be built on a permanent foundation.
  12. How does the proposal deal with the potential loss of vegetation from the development of ADUs?
  • The UDC allows flexibility in terms of where an ADU is placed so that property owners can choose to retain vegetation. For example, a property owner could potentially build a two-story ADU to reduce the building's footprint and retain a mature tree.
  1. How does this proposal for ADUs help with providing accessible housing for seniors?
    • The City of Tucson adopted an Inclusive Home Design Ordinance in 2007 which requires certain accessibility standards, such as a zero-step entry for the structure.
  2. How does this proposal address privacy mitigation?
    • The ADU would be subject to the zone’s setback requirements, which typically require a structure to be set back at least 6 feet from a side or rear property line. Any structure over 9 feet must set back even further. Therefore, higher structures must be located towards the interior of the site, serving as a form of privacy mitigation for taller structures.
    • Should a property owner request to reduce the required setbacks through a Design Development Option (DDO), site-specific conditions can be added to mitigate the potential impacts.
  3. Could an Accessory Dwelling Unit be built in the front yard of an existing home?
  • The current proposal does not allow for detached ADUs to be built in front of a primary structure.
  1. How does the proposed ADU ordinance help regulate existing unpermitted casitas?
    • The proposal does two things to help with the adherence to building and zoning codes.
      • The restriction on kitchens for sleeping quarters has led to many property owners either (1) permitting structure with a kitchenette, then adding the Kitchen after the inspection, or (2) building a structure without getting permits. This proposal would encourage those looking to build an ADU with a kitchen to get the appropriate permits.
      • The City is looking to create an amnesty program, such as what has been developed in other communities like Durango. This would allow for those sleeping quarters that would like a full kitchen or unpermitted structures to go through a process to have their structures permitted.
  2. I live in a neighborhood covered by a Homeowners Association (HOA). Can I build an ADU?
    • That depends on any regulations put in place by your HOA, often referred to as Covenants, Conditions, and Restrictions, or CC&Rs. These are private agreements that are, in general, more restrictive and applied in addition to zoning. For example, a property may be allowed to develop an ADU per their zoning classification, but if their HOA prohibits them, they would be in violation of their HOA regulations if they were to develop an ADU.
    • Homeowners can advocate for their HOA to modify existing CC&Rs using the prescribed process for changes.
  3. What impact could this proposal have on National Register Historic District status?
    • The current proposal does not allow for detached ADUs to be built in front of a primary structure.
    • For a historic district to keep its status it must maintain a level where 50% of its structures are listed as contributing.
    • The items that lead to the delisting of contributing structures are changes to the primary façade, additions of solid walls over 48” in front of the contributing structure, etc., not the development of an accessory building behind a historic structure. Even if that structure were taller than the primary structure and can be seen from a public right-of-way. The development of an ADU in a backyard would not impact a building’s contributing status and would not affect a neighborhoods’ National Register Historic District status.
    • While property owners may choose to make modifications to their property that could potentially delist it, such as building a wall in front, they do have an incentive to maintain the contributing status of their home in order to receive a property tax break.
    • Currently, no City of Tucson historic design review is required for work done to properties in a National Register Historic District that are not an HPZ. Construction of an ADU would not be regulated differently.
  4. How would this proposal affect properties within a Historic Preservation Zone (HPZs) and Neighborhood Preservation Zone (NPZs)?
    • HPZ, HL and NPZ design standards and review process will continue to be required in those areas. This means that an Accessory Dwelling Unit proposed within an HPZ, HL or NPZ must comply with the design standards and review process of the district where it is proposed to be built.
  5. How was this proposal developed?
    • Mayor and Council directed staff to develop a code amendment to allow Accessory Dwelling Units in November 2020.
    • The draft proposal for ADUs was developed based on staff analysis, feedback from the public at previous public meetings, input received via an online survey, and discussions amongst a stakeholder group.
  6. How was the stakeholder group formed and who is represented in this group?
    • A stakeholder group was created to advise the development of this code amendment. The group has been meeting monthly since December.
    • The group was formed based on input from Mayor and Council - it includes architects, real estate professionals, housing advocates, and neighborhood representatives.
    • Members include:
      • Alice Roe, Campus Community Relations Council
      • Allyson Solomon, Metropolitan Pima Alliance
      • Bill Mackey, Worker, Inc/UA CAPLA
      • Bob Schlanger, Jefferson Park
      • Bonnie Poulos, Tucson Residents for Responsive Government
      • "Chico" Valencia, Pascua Yaqui Tribe
      • Colby Henley, Rincon Heights Neighborhood Association
      • Colleen Nichols, Jefferson Park
      • Corky Poster, Poster, Mirto, McDonald
      • Dante Archangeli, Tucson Artisan Builders
      • Diana Lett, Feldmans
      • Gigi Aldridge, Pima County Community Land Trust
      • Hal Bergsma, Arizona AARP
      • Jacqueline Turchick, Barrio San Antonio
      • Jason Wong, Red Point Development
      • Jim Murphy, Tucson Housing Foundation
      • Jonathan Bean, UA CAPLA
      • Josie Zapata, Miles Neighborhood
      • Lee Marsh, Rincon Heights
      • Lisa Bowers, TED Permitting
      • Maggie Amado-Tellez, Pima County Community Land Trust
      • Marcos Ysmael, Pima County Housing
      • Margaret Kish, Catalina Vista
      • Mari N. Jensen, Blenman Elm
      • Mark Holden, Pima County Planning
      • Patrice Lange, Blenman Elm
      • PennElys Droz, Sustainable Nations
      • Peter Norback, Miles Neighborhood
      • Richard McDonnell, West University Neighborhood Association
      • Ryan Stephenson, Pima County Housing
      • Sergio Varela, Pascua Yaqui Tribe
      • Sharayah Jimenez, Cuadro Design
      • Shawn Cote, Southern Arizona Home Builders Association
      • Steve Huffman, Tucson Association of Realtors
      • T. Van Hook, Habitat for Humanity
      • Ted Warmbrand, Barrio San Antonio
      • Timoteio Padilla, Sustainable Nations
      • Valerie Lane, Realtor/Architect
      • W. Mark Clark, Pima Council on Aging

[1] Jake Wegmann & Karen Chapple (2014) Hidden density in single-family neighborhoods: backyard cottages as an equitable smart growth strategy, Journal of Urbanism: International Research on Placemaking and Urban Sustainability, 7:3, 307-329, DOI:10.1080/17549175.2013.879453