Accessory Dwelling Unit (ADU)

​A subordinate dwelling situated on the same lot with the main dwelling and used as an accessory use. There are two basic types of ADU: Attached and Detached. “Attached" is an integral part of the main residence while “Detached" is a separate and independent structure. An ADU contains all the amenities to function as an independent, operational, dwelling unit, including a kitchen, bathroom, living area, and sleeping quarters.​

Building Height

The vertical distance measured from the higher of the natural grade level or the finished grade level established by the Planning and Development Department pursuant to the floodplain or Grading and Drainage Regulations of the City to the highest level of the roof surface of flat roofs or to the mean height between eaves and ridge of gable, gambrel, or hip roofs. ​

Short-Term Rental (STR)

​Rental of any living quarters for 30 days or less (building code). ADUs are prohibited from being used as Short-Term Rentals. For more information, visit phoenix.gov/STR​.

Single-Family Residence District

The list of Single-Family and One-Family residence districts is online: https://phoenix.municipal.codes/ZO/6.​
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•​​​​​ An ADU is prohibited from being used as a Short-Term Rental.  (This provision does not prevent the primary dwelling unit from being used as a Short-Term Rental.)

•​​​​​ No more than one ADU per single-family detached lot may be constructed.

•​​​​​ A detached ADU may be located within the required rear yard and may not exceed 15-feet in height, unless a use permi​t is obtained for height greater than 15-feet.

•​​​​​ ​A detached ADU may be located no closer than 10-feet to a street side property line; 3-feet from an interior property line, and 0' from a property line abutting a fully dedicated alley.

•​​​​​ An attached ADU may project into the required rear yard and may not exceed 15-feet in height, unless a use permit is obtained for height greater than 15-feet.

•​​​​​ An attached ADU may be located no closer than 3-feet from the rear property line and any closer to a side property line than allowed by the zoni​ng district, unless a use permit is obtained.

•​​​​​ An ADU must comply with lot coverage requirements for the lot, though most have been increased.

•​​​​​ For up to lots 10,000 square feet in area, the maximum size of the ADU is 1000 square feet or 75% of the gross floor area of the primary dwelling unit, whichever is less.

•​​​​​ ​For lots over 10,000 square feet in area, the maximum size of the ADU is 3000 square feet, or 10% of the net lot area, or 75% of the gross floor area of the primary dwelling unit, whichever is less.​​​​​​​​​

Determine your property's zoning district through My Community Map​. Enter your address in the search bar,​​​​

click “Zoom to” in the pop-up, close the little window, and click on your lot. A pop-up appears with your Zoning District.

Find your Zoning district in the Zoning Ordinance for setbacks and base lot coverage allowance by clicking the link to the Phoenix Zoning Code​.

Determine your current lot size and how much coverage you currently have. (Maricopa County Assessor) https://mcassessor.maricopa.gov/​.  Enter your address in the search bar. Please note, Maricopa County records may not reflect the same lot size as City of Phoenix records.

Then click on the APN number.

In the Property Information box find your lot size. This is listed in square feet.

Maricopa County also provides approximate floor plans. To find these, scroll down to the bottom of the page and find your building sketch. Add the areas of the main house, any carports, garages, and covered patios (uncovered patios are not counted). Any other detached structures, regardless of size such as tool sheds, ramadas, or storage containers/buildings, must be included in your lot coverage calculation. Measure any structures not shown on the assessor's sketch and add the square footage to the total area covered. The site plan and floor plan provided must be drawn to scale to be used for permit approval. 

If you have unpermitted buildings on your property, please contact pdd.ombudsman@phoenix.gov to learn how to apply for a permit to legalize them before pursuing the ADU permit.

Take the total area of all structures on your lot and divide it by the​ lot size shown on the Assessor’s website. The result is the percentage of your lot currently covered. An example of how to create a plot plan.

Take your lot size and multiply it by the percentage allowance (40% = 0.40, 25% = 0.25 etc.) in the zoning ordinance table (see Find your Zoning District). The result is the amount of square footage you are allowed under roof. Subtract the square footage of all current structures from what you are allowed, and you will know how much buildable area you have left. See the ADU guidelines (section 608 of the Zoning Ordinance) for any additional allowances to lot coverage for the ADU and limitations on ADU size based upon your lot size).

Example using the above diagram:

Area of buildings

Main floor of house-1769 Sq. Ft.

Garages-504 Sq. Ft. plus 522 Sq. Ft. = 1026 Sq. Ft.

Covered patios- 300 Sq. Ft. plus 108 Sq. Ft. = 408 Sq. Ft.

Storage building: 80 Sq. Ft.

Total area under roof: 1769+1026+408+80= 3283 Sq. Ft.

Area of lot: 10,000 Sq. Ft.

Percent covered = 3283 divided by 10,000 = 32.83%

If you have unpermitted buildings on your property, please contact pdd.ombudsman@phoenix.gov​ to learn how to apply for a permit to legalize them before pursuing the ADU permit.​​​​

Whether you are considering an attached or detache​d ADU, you will need to determine where your building setbacks are to understand where on your property you can place the new ADU structure. The easiest way to do this is to create a plot plan of your property (you will need one for permitting purposes.​)

If you plan to convert an existing garage or carport to ADU, you will need to create off-street parking spaces in dustproof conditions. These parking spaces must not be located in the front yard setback.​​​​​​

See the plot plan example guide: https://www.phoenix.gov/pddsite/documents/TRT/dsd_trt_pdf_00285.pdf

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