Accessory Dwelling Units FAQ

The following are responses to Frequently Answered Questions that have been asked throughout the Accessory Dwelling Units (ADU) Code Amendment process. They have been organized into the following ten categories, to help you navigate to the information you seek.

Current Regulations and ADU Proposal

What is the proposal to allow Accessory Dwelling Units?

The 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 may also be used
  • Each newly constructed ADU would be required to have a cool roof

What extra units are currently allowed and what would be allowed under the proposed rules for Accessory Dwelling Units (ADUs)?

Property owners can currently build two kinds of extra units on their residential lot. These options are called Sleeping Quarters or a Second Residential Unit.

Sleeping Quarters are allowed to be built on most residential lots. Sleeping quarters can be up to 50% the size of the main house, and can be a maximum of 12 feet high. A full kitchen is not permitted. Only a sink, small fridge, and microwave are allowed.

Second Residential Unit can be built if the residential lot is large enough, based on the zone. For example, in an R-1 zone, the most common zone across the city, a Second Residential Unit can be built if the lot is over 10,000 square feet. A full kitchen with an oven is allowed.

If Accessory Dwelling Units are allowed, property owners could build an extra unit on any residential lot, and the unit could include a full kitchen.

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

Sleeping Quarters
Second Residential Unit
Accessory Dwelling Unit (ADU)
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 > 10,890SF
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
Parking 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
Setbacks 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 None 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

Proposed ADU Size and Development Standards

We have concerns that the allowable size of the ADU is too large for the scale of our neighborhood. What impact will the allowance for 1,000 sf on larger lots have?

  • The ADU proposal is very similar to both other peer cities and the AARP ADU model ordinance. As is the case with currently allowed guest houses / sleeping quarters and second units (where allowed), most homeowners do not choose to develop to the max allowable unit size. The larger size allows for the flexibility to allow for accessibility for those in wheelchairs or that are physically disabled, to include 2 bedrooms for a small family, which is a significant need in the Tucson housing market. It should also be noted that beyond the size, the development potential is also still limited to standards of the zoning, 70% lot coverage, setbacks, building height etc.

What are the rules to maintain privacy when building an ADU?

  • 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. An example of this is if a homeowner were to propose a 24’ building, it would be required to be setback 16 feet from the property line. Essentially, the taller the building, the more it must be setback. This is exactly the same as if a property owner were to add a second story to their house, or build a two story addition.
  • Should the homeowner choose to build a two story structure, but need a reduced setback due site constraints, such as a mature tree, the Design Development Option (DDO) process may be utilized. This process has findings it must meet that address privacy and viewscape, requires notification of all property owners within 100 feet, and provides the opportunity to add conditions to mitigate the impact.

How many total units, besides the principal structure, will be permitted on a property. Please include all combinations of guesthouses, sleeping quarters and ADUs in each zoning including the larger zone classifications such as SR, RX-1 and RX-2.

  • This proposal would allow for one ADU on each residential lot, in addition to what is currently allowed in all zones for residential uses. We cannot specify how many total units would be permitted on lots in a given zone, as development potential is governed not just by the zone, but also the lot size and other factors. There is no specified limit to the number of sleeping quarters (or other accessory structures, such as sheds) which may be developed on a lot so long as the development standards of the zone are met (lot coverage, setbacks, maximum combined size of accessory structures must be 50% of principal structure, etc,). For example, one could have a 1-acre lot in a R-1 zone and build multiple sleeping quarters on it in addition to the principal structure. Understanding that, the following is a snapshot of what would be permitted in certain residential zones as a residential use (ADUs would also be permitted in commercial zones and other zones that allow residential use). Additionally, some of these zones allow multifamily use (3 or more units), however this is not reflected as ADUs would only be permitted on lots with one- or two-family residences):
  • RH, SR, SH, RX-1, & RX-2 Zones: 1 principal structure + 1 ADU + sleeping quarters/accessory structures
  • R-1 Zone (>10,000sf lot size): 2 residential units + 1 ADU + sleeping quarters/accessory structures
  • R-1 Zone (<10,000sf lot size): 1 principal structure + 1 ADU + sleeping quarters/accessory structures
  • R-2 Zone (>5,808sf lot size): 2 residential units + 1 ADU + sleeping quarters/accessory structures
  • R-2 Zone (<5,808sf lot size): 1 principal structure + 1 ADU + sleeping quarters/accessory structures
  • R-3 Zone (>5,000sf minimum lot size): 2 residential units + 1 ADU +  sleeping quarters/accessory structures

Will this allow tiny homes?

  • “Tiny home” is a term that can be applied to a number of types of homes, but are generally defined as a home that is 400 square feet or less. The maximum size for an ADU is 1,000 square feet, so some people might call them tiny homes. It’s important to note that the updated ADU proposal does not allow “tiny homes on wheels,” which are considered a vehicle, rather than a dwelling. Like all new construction, ADUs must be built on a permanent foundation.

Owner-occupancy / mini-dorms / short-term rentals

Will a property owner be required to live in the ADU or primary home?

  • The ADU proposal does not regulate occupancy of an ADU or the main house 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, such as a need to relocate, this requirement could be a liability.
  • Occupancy is not regulated for other types of housing and is not regulated elsewhere in Tucson’s 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.
  • A recent Housing Study found a racial gap in homeownership in Tucson - 68% of white households own their home, compared with 55% of Hispanic households and 36% of Black households. An owner-occupancy requirement could reinforce these inequites by benefiting homeowners over renters.
  • Many other cities which have required owner-occupancy for sites with an ADU, such as Minneapolis and Seattle, have removed this restriction after finding that it was a barrier to ADU development.
  • According to a study by the Oregon Department of Environmental Quality, more than two-thirds of properties with ADUs are owner-occupied even without an owner occupancy mandate3.

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[1].
  • Some ADUs may be used for short term rentals. But allowing full kitchens makes them more appealing for longer-term residents. They will likely be used for a variety of living arrangements, including multigenerational housing, hosting visiting family members, or renting to people in search of housing in Tucson neighborhoods.

How are ADUs different from mini-dorms?

  • ADUs would have to 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.
  • The proposal would limit an ADU to a maximum of 1,000 square feet, which is large enough to potentially allow a 2-bedroom unit. Mini-dorms are significantly larger and generally greater than 2,300 square feet in size

Could an ADU be purchased separately from the main home?

  • For an ADU to be owned separately from the main house, the lot would need to be split into two. The two new lots must both meet minimum lot size requirements, which are 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. It would become the primary residence.

Historic Preservation

How would this proposal affect properties within a Historic Preservation Zone (HPZs) and Neighborhood Preservation Zone (NPZs)?

  • Historic Preservation Zone, Historic Landmark (HL) and Neighborhood Preservation Zone 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.

What is the impact of this ADU ordinance on National Register Historic District status?

  • The proposal does not allow for detached ADUs to be built in front of a primary structure.
  • In general, 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., In nearly all cases, we do not anticipate the development of an ADU in a backyard (even if two stories) would impact a building’s contributing status. Even in those rare cases where it could possibly delist a property, the experience in other cities is that the development of ADUs is generally spread out and not in large enough numbers to likely 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 available to owner occupied homes.
  • Currently, no City of Tucson historic design review is required for new construction or work done to properties in a National Register Historic District that are not an HPZ. It is incumbent on the property owner to clear any modifications with SHPO to ensure that they retain their property tax exemption. The City of Tucson does, however, encourage property owners to submit their plans to SHPO for a review when proposing any changes, such as an addition or an ADU should this ordinance be adopted by Mayor and Council.


What is the impact of allowing for a parking waiver for sites near transit or bike infrastructure or to park on-street when available?

  • From previous experience many property owners will still choose to provide parking on-site, even if it isn’t required, for security reasons or ease of access to their automobile. Because of the dispersed nature of ADU development, we do not anticipate the passage of this proposal having a significant impact on on-street parking throughout a street or neighborhood. In specific locations where negative situations may arise, the City has the Parkwise parking program to help address those problems.
  • There are also negative impacts when we require more parking on-site when it is not needed. This would help to avoid unnecessary on-site paving and the removal of existing vegetation, a commonly noted concern of some neighborhood groups. Additionally, requiring parking when it is not necessary, only increases costs for a program that is intended to help with housing affordability.

Code Enforcement

How does the updated ADU proposal 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 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 has proposed an amnesty program to allow property owners to permit previously unpermitted ADUs or add a full kitchen to sleeping quarters.

How would the Amnesty program work?

  • The amnesty program is still in development and there will likely be some additional refinement based on feedback from Mayor and Council, should the zoning changes be adopted. Some aspects we are looking at are:
    • A waiver of the penalty fee for unpermitted structures, which otherwise doubles the total permit fees. This waiver may be subject to criteria, for example only available to property owners residing on the property.
    • A compliance permit which allows the structure to be permitted based on an inspection to verify life safety standards and does not require a full plan set.
    • Additionally, the Department of Housing and Community Development has proposed a pilot program to fund improvements and repairs to existing ADUs or sleeping quarters to make them habitable and bring them into compliance with building code standards. This program would be available to eligible low-income homeowners.

Sustainability and Climate Goals

How do ADUs address sustainability and the City of Tucson’s climate goals?

  • When ADUs are built in existing neighborhoods, they connect to and use existing infrastructure like utilities and transportation networks. This is different from sprawl and development on the outer edges of the city where new infrastructure has to be built, costs more, and people and resources have to travel farther.
  • ADUs are one way to increase density in less dense neighborhoods. When more people live in the same area, investments in public transportation, connected bike networks and better walking environment benefit more people, and can work better.
  • If a household can afford to live closer to job centers and work opportunities by living in an ADU, they might drive less time to get to work, or be able to take a bus for a shorter journey.
  • New construction of ADUs must meet current building code and energy code standards. These have been updated in recent years and are more efficient than standards used for older housing.

What impact will the development of ADUs have on heat generation and the Urban Heat Island (UHI) Effect?

  • As a way to help lessen the UHI, the ADU update would require that newly constructed ADUs include a “cool roof.”
  • Research generally shows that increasing density gradually, the way that ADUs are built, will not in itself increase UHI effect for a specific area.
  • A local development project called Civano Phase 1 included reflective white cool roofs. A research project showed that the new cool roofs resulted in cooler temperatures than nearby neighborhoods without them. 2
  • Additionally, new construction with a light-colored cool roof can actually reduce temperatures compared to the same area left with barren ground.

How does the proposal deal with the potential loss of vegetation from the development of ADUs?

  • Current residential zoning allows for 70% lot coverage, this is not a change related to ADUs. The proposed amendment would simply allow for an ADU within the allowed lot coverage, subject to the additional standards for ADUs. Additionally, this is a consideration with any new development, not just ADUs. If a property owner were to build an addition, second unit (if allowed), a garage, a guest house, a shed, etc., there are currently no requirements to preserve mature canopy trees.
  • Allowing for flexibility, in terms of where an ADU is placed allows property owners to choose a location that could retain vegetation. For example, a property owner could potentially build a two-story ADU to reduce the building's footprint or use a DDO for reduced setbacks in order to retain mature vegetation.

How does this proposal help address urban sprawl?

  • ADUs alone will not stop sprawl, and even with the passage of an ADU ordinance, our development patterns will continue to extend outward. ADUs are only one tool of many that the city is pursuing to promote infill development as well as thoughtfully planned development at the edge of our city as a balanced approach to growth. ADUs can help provide more housing in already developed areas in our core, which is in high demand.


What is affordable housing and how do ADUs help address housing affordability?

Affordable Housing is housing that a household can pay for and still have enough money left over for other needs like food, transportation, and healthcare. The federal government (Department of Housing and Urban Development, or HUD) typically defines housing as affordable when it costs 30% or less than the household’s total income.

While all ADUs are not necessarily affordable by HUD standards, they help to provide a more housing types and options. For example:

  • The cost to rent an ADU is generally less than other rental options in the same neighborhood[2].
  • When people rent ADUs, people with different income levels are more likely to become neighbors than through renting other types of unsubsidized rental housing.
  • The “supply effect” - supply and demand play an important role in housing prices. Increasing the housing supply takes pressure off demand and reduces the pricing power of the landlord. Allowing ADUs is just one way to increase the number and options for housing in Tucson.
  • ADUs are limited to a maximum of 750 square feet or 1,000 square feet. Less square footage = lower rent.

Additionally, the City is pursuing programs to help make ADUs more affordable.

For property owners that would like to build an ADU:

  • Funding for improvements or repairs to make an ADU safe and habitable
  • Pre-approved model-plans to be used by property owners to help reduce costs.
  • Partnerships with local organizations to help provide technical assistance to low- and moderate-income households to assist with the design and permitting process

For people who would like to rent and live in an ADU:

  • Federal Housing vouchers to subsidize the rent paid to the landlord.

Will ADUs solve the City of Tucson’s affordable housing issues?

  • ADUs are just one of many tools Tucson will need to use to address a complex problem such as housing affordability.
  • Other household costs contribute to affordability. For example, if a household can afford to live closer to job centers and work opportunities, (another benefit of ADUs and increasing density in city centers) their transportation costs may decrease.
  • ADUs can be designed to fit the needs of specific households. Many will be significantly smaller than the maximum size. Modular and pre-fab construction options can also help bring down costs.
  • As stated above, the City is also exploring supportive programs to help reduce costs of construction and to aid with affordability. Examples of this:
    • Funding for improvements and repairs to existing casitas
    • Partnerships with local organizations to conduct outreach and provide technical assistance to low- and moderate-income households
    • Work with community partners such as AIA to develop model plans that can be used to bring down costs
    • Explore local funding sources and options to provide financial assistance such as low-interest loans

How do ADUs help address housing and opportunity equity?

  • ADUs are commonly built in low-density residential neighborhoods where lower-cost housing might not be available. Generally, people who choose to rent smaller homes like ADUs may be able to afford to live in neighborhoods with higher rents. These neighborhoods might have quality schools, public libraries, and be closer to job centers, public transportation, parks and grocery stores. Allowing ADUs is one way for a city to promote more housing options, and a mix of housing prices in more neighborhoods to help make these parts of daily life accessible to more people.

How do ADUs support multigenerational housing and changing societal preferences?

  • Multiple living units on one lot provide flexible living options for different generations of a family. Older family members can maintain independence in a separate living space like an ADU, but still live close to family for support, social connections, and other shared resources.
  • Many other family groupings could benefit from this flexibility, including young families saving for a future home, or disabled but independent family members that need some caregiving.

How does this proposal for ADUs help with providing accessible housing for seniors?

  • Increasing options for seniors to “age in place” in more dense, walkable, connected neighborhoods increases their access to available services and networks, nearby neighbors, and can reduce the dependence on driving to access daily needs.
  • The City of Tucson adopted an Inclusive Home Design Ordinance(PDF, 724KB) in 2007 which requires certain accessibility standards, such as a zero step entry for the structure.

Quality of Life / Neighborhood Character

What are ADUs effect on neighborhood stability and housing values?

  • As property values increase, so do the property tax rates. If a homeowner cannot afford the cost of increased property taxes, they may be forced to move. The option for a property owner to generate passive income can help support the property owner’s cost of living in that area. Additional income can also help support their mortgage payments.
  • Building on the property adds value to it because the owner is investing in their property. Neighbors benefit from this investment too. This is called a positive externality where the increased value of a neighbor’s property also increases values on their neighbor’s property.

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.
  • If this is a barrier for homeowners who wish to build an ADU, homeowners can advocate for their HOA to modify existing CC&Rs using the prescribed process for changes.

Currently, without the ADU Code Amendment, carports and garages that are built on property lines are being converted to ADUs. Will this make things worse?

  • Should the ordinance pass, any structure either being constructed as an ADU or converted to an ADU would be required to be permitted and meet building and zoning codes, including setbacks. If they were to need relief from setbacks they would need to go through the Design Development Option (DDO), which requires them to meet findings related to privacy, noise, light, and for surrounding property owners within 100 feet to be notified for comment.

We have concerns about the impact on city services that go along with increased density. How will increased density affect services such as code enforcement, trash pickup, and police response?

  • The proposed ADU code amendment and subsequent affordability and amnesty programs should result in more permitted structures and help with overall code enforcement issues compared to the status quo. Should the ordinance pass, any structure either being constructed as an ADU or converted to an ADU would be required to be permitted and meet building and zoning codes. One of the primary reasons that many current guest houses / sleeping quarters do not get permits or meet code is because they are not permitted to have full kitchens. The passage of this proposal would now allow for those structures to be built with kitchens and encourage people to permit them.
  • Additionally, while code enforcement and other issues with city services are not within the scope of an ADU zoning code change, development patterns supported by our zoning code do help to influence how those city services are funded. Additional density adds to our City’s tax base, providing a more stable funding base for services and infrastructure.

Outreach and Public Input

How was this proposal developed?

  • The Mayor and Council directed City staff to develop a code amendment to allow Accessory Dwelling Units in November 2020.
  • The updated 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 with a stakeholder group.
  • Two series of public meetings were held which included three virtual meetings in February 2021 and four virtual meetings in May 2021. Over 400 community members attended these meetings.
  • Over 550 community members responded to an online survey to provide feedback on the proposal
  • Over 100 comments were submitted to the Planning Commission and 30 people spoke at the Planning Commission Public Hearing.
  • All of this significant input informed the proposed code amendment developed by staff as well as the Planning Commission recommendation to Mayor and Council to adopt the proposed code amendment.

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
    • "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


[2] 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