Alameda County


September 8, 2022

Alameda County, California


Alameda's ADU code has been amended to comply with recent state regulations. The most recent specifications for approving an ADU in this community are listed below.


ADUs are permitted in any zoning district that allow single-family or multi-family residential use. ADUs may be denied if their creation would have a negative impact on traffic flow or public safety, or if adequate water and sewer service is not available, as determined by the County.


Single Family Lot

  • On a lot with an existing or proposed single family dwelling, one (1) ADU (attached or detached) and one (1) Junior ADU are allowed.

Multi-family Lot

  • On a lot with an existing multifamily dwelling structure (2 units or more), multiple attached ADUs are allowed up to 25% of the number of existing units. Attached ADUs must be created through the conversion of existing space in the structures not used as livable space, such as, storage rooms, boiler rooms, passageways, attics, basements, or garages. In addition, a maximum of two (2) detached ADUs are allowed on a lot with an existing multifamily dwelling structure and they may be attached to each other.


The maximum square footage you can build depends on your ADU type:

  • JADU: 500 sq. ft.
  • Detached ADU: 800 sq.ft.

All new construction ADUs, attached and detached, are subject to the maximum unit sizes:

  • 850 sq. ft. (one bedroom or less) or 
  • 1,000 sq. ft. (more than one bedroom) or 
  • 1,200 sq. ft. for properties in Agricultural (Ag) zoning, regardless of bedroom count 


ALL attached ADUs over 800 sq. ft. on parcels with single-family dwellings shall not exceed 50% of the primary dwelling living area.

ADUs created by conversion are allowed up to 1,000 sq. ft. as long as it does not exceed 50% of the primary dwelling area; ADUS created by conversion on Ag zoning are allowed conversions of up to 1,200 sq ft. 

A Site Development Review is required for ADUs wishing to exceed the above standards.


  • Attached ADUs: standard for the zone district (usually 28 ft)
  • Detached ADUs outside the Urban Services Line: standard for the zone district (usually 28 ft)
  • Detached ADUs inside the Urban Services Line: 16 ft (21 ft allowed with Zoning Administrator approval)
  • ADUs above Detached Garages inside the Urban Services Line: 24 ft at the roof peak, 20 feet at top of exterior wall


An ADU may be created on any lot where the zoning regulations allow residential uses and has an existing or proposed single-family dwelling or a multifamily dwelling structure. ADUs are also allowed in mixed-uses zones where residential uses are allowed together with nonresidential uses, including residential above ground-floor commercial, for example.


  • JADUs are contained entirely within the singlefamily dwelling (including attached garage), and are subject to the same setbacks and development standards as the primary zoning district.
  • Minimum setbacks of 4 ft from the side and rear lot lines are required for new construction ADU of any size, both attached and detached. 
  • Detached ADUs over 800 sq ft must provide a minimum 10 ft separation from the primary house, and 6 ft from accessory structures. 
  • New construction attached ADUs are allowed same height as main house (80% second story rule applies)
  • New construction detached ADU limited to 16 ft, one-story. 
  • For ADUs contained entirely within an existing, permitted, single-family residence or related accessory structure, with no change in building volume, the minimum setbacks are whatever is required for fire and safety.


Off-street Parking Requirements

No additional parking is required when:

  • Property is within ½-mile walking distance of public transit 
  • Property is within an architecturally and historically significant historic district 
  • ADU is entirely within the existing interior space of the primary residence or accessory structure (e.g. sheds, garages, carports, covered parking structures, etc.) 
  • On-street parking permits are required but not offered to the ADU occupant 
  • A car share vehicle is located within one block of the ADU

For attached or detached ADUs requiring new construction (e.g. a new accessory building or an addition), one parking space is required per unit or per bedroom, whichever is less. These spaces may be located in setback areas or provided through tandem parking on a driveway. 


  • Owner occupancy of the property is not required for standard ADUs.
  • Only applications for a Junior ADU must the applicant be the property owner and current occupant of the property


Planning Fees

  • ADUs that are contained entirely within an existing, permitted residence or related accessory structure, with no change in building volume, are not subject to any Planning fees. 
  • ADUs that require construction of an addition or new detached building and are 750 sq ft or larger in size, are subject to a Park Dedication fee.** 
  • New construction ADUs wishing to exceed the maximum building height and/or unit size are subject to a Site Development Review fee.** 

**Please see Zoning Counter staff for the appropriate fee amounts. 


Permit Fees

Permit fees vary primarily based on ADU size and project valuation. Other factors can affect the cost of the permit, including but not limited to, other work that may be necessary to facilitate an ADU project, the quality of the plan submittal, and incomplete drawings that require multiple rounds of City review. Please check with the Permit Center for actual fees for your application.


Impact Fees

The City does not apply development impact fees to ADUs and JADUs. While ADUs are separate dwelling units, they are accessory uses to a primary residence.


  • ADUs and JADUs may not be rented for a period of fewer than 30 days.
  • ADUs and JADUs may not be sold or conveyed separately from the main residence.
  • ADUs shall match the exterior material, color, and roof form of the permitted primary dwelling structure.
  • ADUs shall appear subordinate to the existing primary dwelling in terms of size and location.
  • Exterior access is required for ADUs and JADUs.
  • ADUs contained entirely within an existing permitted, detached accessory structure may be allowed an expansion of no more than 150 sq. ft. beyond the same physical dimensions as the existing detached accessory structure. The expansion is limited to ingress and egress purposes only.
  • In Agricultural (Ag) Districts, where allowed, ADUs shall be located on the same building envelope as the existing or proposed primary dwelling. Any exceptions will require a Site Development Review permit.
  • Agricultural (Ag) District parcels are subject to East County Area Plan (ECAP) limitations as applicable.



Contact for general ADU information:

Permit Center/Zoning Counter

399 Elmhurst Street, Suite 14, Hayward, CA 94544


Contact for ADU regulations update status information

Rodrigo Orduña

Alameda County Planning Department

224 West Winton Avenue, Suite 11, Hayward, CA 94544


This quick reference manual should be useful to you while you work on your ADU project. Our in-house permit technician will process your permit on your behalf without adding any markups as part of our service if you choose to construct with us.

Please don't hesitate to schedule a meeting with us if you're interested in building with ADU.Works or to give us a call at (650)-227-4810. We are happy to answer any questions you may have and go over the details of how your permission will be processed. Our staff is eager to hear from you.