Accessory Dwelling Units (ADUs)

Frequently Asked Questions

General Questions

What is an “Accessory Dwelling Unit”?

ADUs are attached or detached residential units that provide complete independent living facilities, and are also known as second units, in-law units, or granny units. An ADU must be located on the same lot as a proposed or existing primary residence and may be created via the following methods:

  • Building a new detached accessory structure
  • Converting an existing legally constructed accessory structure
  • Building an addition attached to the primary dwelling
  • Converting space in the primary dwelling (e.g., basement)
  • Junior ADU: a JADU is created entirely within the space of an existing or proposed single family home and is not more than 500 square feet

What’s new in the world of ADUs?

On January 1, 2023, new laws in California came into effect that reduce barriers and streamline the approval process for ADUs. ADUs are permitted on single family lots, multifamily lots, and mixed-use zones. The property owner occupancy requirement is no longer required for ADUs. However, the owner occupancy requirement still applies to Junior ADUs. State law now provides as a basis that a detached ADU up to 800 square feet in floor area, and up to 18 feet in height, with 4-foot side and rear yard setbacks, are permitted provided it meets other development standards.

Where are ADUs allowed?

ADUs are permitted on properties that are zoned to allow residential use and have an existing or proposed primary residence on the same lot.

How many ADUs are allowed?

  • 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.
  • Multifamily Lot: On a lot with an existing multifamily dwelling structure (2 units or more), any number of accessory dwelling units are permitted through the conversion of existing space in buildings. Each unit shall comply with state building standards for dwellings. 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.

Must the applicant for an ADU be the Current Owner and Occupant?

Only applications for a Junior ADU must the applicant be the property owner and current occupant of the property. Prior to issuance of a JADU permit, the applicant will be asked to provide a copy of a recorded Declaration of Restrictions at the Alameda County Recorder’s Office using the appropriate City form.

Can I use my ADU as a short term rental (e.g., AirBnB)?

No, ADUs may be rented, but the rental period of any ADU must be for a term longer than 30 days.

Can I sell the ADU?

No, ADUs may not be sold or otherwise conveyed separately from the primary dwelling.

Can I demolish my garage to build an ADU?

Yes, an existing garage may be demolished to make room for a new ADU. However, if the garage that is to be demolished was constructed prior to 1942, then a Certificate of Approval application is required. The Certificate of Approval application is necessary so that the City can determine whether the garage is a historic resource, and under 2023 ADU law the City no longer requires a public notice for this type of Certificate of Approval application.

Is neighborhood notification required when adding an ADU?

No, state law mandates ministerial review for all ADU applications so there is no public notification.

Development Standards

See Alameda Municipal Code Section 30-5.18 for regulations.

30-5.18 - General Provisions and Exceptions for Accessory Dwelling Units | Code of Ordinances | Alameda, CA | Municode Library

Are ADUs subject to lot size requirements and density limitations?

No, 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 non-residential uses, including residential above ground-floor commercial, for example.

Are there restrictions on the size of an ADU?

The total floor area of an ADU cannot exceed 1,200 square feet, provided however an 800 square foot ADU must be allowed. Floor area is defined as the total area of all the floors measured from the exterior faces of the building with ceiling heights of 7 feet or more. This definition includes space in basements, storage rooms, attics, interior and exterior stairways, covered porches and all areas that are greater than fifty (50%) percent enclosed with walls and covered, but does not include a garage.

Is there a limit on the number of bedrooms in an ADU?

No, but all bedrooms must conform to standard building code requirements such as minimum size and minimum window egress requirements. Refer to the California Building Code or consult a qualified building professional for more information about building code requirements.

Am I required to create a new parking space on my property for the ADU?

There are no parking requirements for ADUs or JADUs.

May I convert my garage into an ADU?

Yes, an existing garage may be converted/demolished in conjunction with the construction of an ADU or converted to an ADU. A separate building permit is required for the demolition of a garage. A Certificate of Approval from the Planning division is required if the garage/structure is a pre-1942 building. The off-street parking space(s) are not required to be replaced. The driveway and curb cut may remain for off-street parking provided the length of such driveway is at least eighteen (18’) feet behind the property line in order to accommodate a parked vehicle without any portion of the vehicle encroaching into the public right-of-way. Remaining driveways that do not meet the minimum eighteen (18’) foot length shall be abandoned per Section 22-18.3 as part of the construction of the accessory dwelling unit. If the driveway does not meet the criteria, the driveway shall be converted to a landscaped area and a licensed contractor shall obtain an encroachment permit to restore the sidewalk, curb and gutter per City of Alameda Standard Plans. California Building Code also has requirements for converting non-habitable space to habitable space. Refer to the California Building Code or consult a qualified building professional for more information about building code requirements. If the ADU is attached to a garage then fire resistive construction will be needed between the garage and the ADU. Garages that are converted to ADUs shall replace garage doors with the same exterior wall material, replacement door/window, and trim as the existing building or the primary dwelling.

Is there a height limit on detached ADUs?

Yes. ADUs may be up to 18 feet tall unless the ADU is being constructed within the existing space of a legally constructed existing accessory structure. The 18-foot height limit is measured from the ground to the ridge of the roof. An additional two (2) feet in height may be allowed to raise the maximum height to twenty (20) feet when the roof pitch on the accessory dwelling unit matches the roof pitch of the primary dwelling unit.

May I have a loft or a second story in a detached ADU?

Yes. A loft or second level is allowed within the envelope of the detached ADU which is 18 feet high and is measured from exterior finished grade to the exterior peak of the roof. All California Residential/Building Code and requirements for habitable space apply such as lighting and ventilation, ceiling height, etc., and habitable lofts open to the main living space require a guardrail. Habitable space above the main floor will also count towards the maximum allowable area of the ADU. In planning for a loft or second level interior volume in the ADU, please be aware of the City’s ADU design standards which require the shape and the pitch of the roof to match the main dwelling. For example, if the main dwelling has a pitched roof, the ADU shall not have a flat roof to accommodate a second level.

Are there design guidelines for ADUs?

Yes. If an ADU requires an exterior addition to the main house or construction of a new detached building within 50 feet of an adjacent street frontage, the ADU must incorporate the same materials, colors, and style of the primary dwelling including roof materials, form, and pitch, eaves, windows, accents, distinctive features, and character defining elements. Creation of the ADU shall not involve any changes to the existing street-facing façade. (Exception: a prefabricated or modular home may be permitted as a new detached unit.)

How does the height limit apply in designated Flood Zones?

Homes located in specially-designated FEMA Special Flood Hazard Areas (Flood Zone) are typically required to build an elevated floor that is higher than the highest level of projected flood waters. If the property is located within a Flood Zone, the ADU may exceed the 18-foot height limit in order to provide an elevated living area that meets FEMA regulations. However, to keep the height exception at a minimum, the interior ceiling height of the living area cannot exceed 8 feet. The ADU must also provide 4-foot side and rear yard setbacks. If your property is within a FEMA Flood Zone, please consult with a Planner prior to submitting your application.

Are there setback requirements for detached ADUs?

Yes. Generally, the structure must maintain a four-foot (4’) setback from side and rear property lines and 5 feet (5’) from street side yard property lines. However, if the structure is more than seventy-five feet (75’) from the front property line and adjoins a neighboring required rear yard, this requirement does not apply, except street side yard property line setbacks are five-feet (5’) from the property line. Also, if the ADU is converted from an existing structure or constructed fully within the location of an existing structure, the setback requirement does not apply. Detached ADUs located in the Flood Zone that are allowed to exceed the 18’ height limit in order to meet FEMA requirements must provide the minimum four-foot (4’) side and rear yard setbacks.

May I build a second story above the garage in my backyard for an ADU?

A second story will only be allowed if the existing garage has the height to accommodate a second story within its existing framework. However, the height of the second story ceiling cannot exceed 18 feet. Otherwise an ADU within an existing garage may include an expansion of no more than 150 square feet beyond the same physical dimensions as the existing garage and any such expansion must be limited to ingress and egress. If you demolish a detached garage, new construction ADU is limited to 18 feet in height.

Are ADUs required to install fire sprinklers?

An ADU is only required to install fire sprinklers if fire sprinklers are required for the primary dwelling.

Are there lot coverage requirements for detached ADUs?

Yes, the total area of all building footprints on the lot cannot exceed 60% of the lot area.

In addition, the footprint of the ADU cannot cover more than 60% of the rear yard setback area or 600 square-feet, whichever is greater. For lots that are at least 100’ in length, the rear yard setback area is 20 feet from the rear property line multiplied by the width of the lot. For lots that are less than 100-feet deep, the rear yard setback is 20% of the lot depth, but no less than 12 feet.

As an exception to the lot coverage requirements above, an ADU that is not more than 800 square feet in size and up to 18 feet tall will be permitted as long as the ADU provides 4-foot setbacks from the rear and side property lines.

Minimum Separation Between Buildings:

There shall be a minimum of six (6’) feet separating all construction (including eaves and similar architectural features) of the detached ADU from the main building(s) or other accessory building(s) on the same lot. The separation requirements of this paragraph may be reduced by the Building Official if one (1) hour fire resistive construction is utilized.

Protected Trees:

No protected tree(s) shall be removed to accommodate an accessory dwelling unit except with the recommendation of a certified arborist and approval procedures set forth in Section 13-21 of Chapter XIII of the Alameda Municipal Code.

Junior ADU

What is a Junior ADU?

State law allows a special type of ADU called a Junior ADU (JADU). A JADU must be located entirely within the existing walls of a proposed or existing single-family home, except that an addition of 150 square feet may be permitted. The JADU must have a separate entrance from the main dwelling that is not on the front elevation of the house. The JADU must also have its own efficiency kitchen, but a private bathroom is not required as long as that the JADU has full access to a bathroom in the primary dwelling. The maximum size of a JADU is 500 square feet. No off-street parking is required. Either the JADU or primary dwelling must be owner-occupied. As part of a JADU permit, the applicant will be asked to provide a copy of a recorded Declaration of Restrictions at the Alameda County Recorder’s Office using the appropriate City form.

Permit Fees

How much are the permit fees for an ADU?

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.

Do development impact fees apply to ADUs?

No, 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.

Building-Related Questions

Can I add an ADU to my garage but keep the garage door and use the space for parking when the ADU is not in use as living space?

No, ADUs and garages are subject to different requirements under the building code and therefore the two uses (occupancy types) cannot be commingled. The codes and regulations exist to protect the safety of building occupants. In this case, the possibility of a person sleeping in the same enclosure as a running vehicle presents a serious safety hazard.

Are there requirements for separate utility connections as part of creating an ADU?

Alameda Municipal Power does not require a separate electric meter for attached or detached ADUs. The additional electrical load of an attached and/or detached ADU may require the applicant to upgrade the existing electrical service. Also, an applicant may choose to apply for separate utilities but should be aware of the additional costs and permits for the voluntary work.

Can I request a separate address for the ADU?

A separate address will be assigned by the City’s Building Official for the ADU as part of the building permit submittal. Applicants do not need to make a separate request.

I am building an attached ADU for a family member, and I want direct access between the primary dwelling and the ADU. May I simply connect the two units with a door between the units?

The California Building Code requires that residential units be separated by a one-hour-rated fire separation. This is true for a two unit building as it is for a multi-unit building. In neither case can a door open directly between the units, because such an opening would pierce the fire separation. Should you wish to design the ability of going from one unit to another without leaving the building, then the design needs to include a common area that is accessible by two units, for instance, a hallway in an apartment building.

Alternatively, you may consider a Junior ADU, which is more conducive to family situations sharing common facilities but has different requirements. See section on Junior ADUs above.

Sample ADU Scenarios

The size of an ADU shall not exceed 1,200 square feet (sf) of floor area

Scenario 1 - Detached ADU

Angel wants to build a detached ADU in her backyard with one bedroom. The maximum size of her detached ADU would be 1,200 square feet and the maximum height would be 18 feet.

Scenario 2 - Converting an Existing Accessory Structure to an ADU

Dan has a 400 square-foot two-car garage in his backyard that he wants to convert to an ADU. He would be able to convert the entire garage to an ADU because the area of the garage-converted ADU is less than 1,200 square feet. Dan may also add up to 150 square feet as part of converting the garage to an ADU for ingress / egress as long as total ADU size is less than 1,200 sf.

Scenario 3 - Expanding the Primary Dwelling to Create an Attached ADU

Joanne’s home is 1,200 sf in size. Below the main floor of her home is a basement that she wants to turn into an ADU with two bedrooms. The basement area is the same as the upper level living space at 1,200 sf. Joanne can convert all of the 1,200 square feet of her basement into an ADU.

Scenario 4 - Multifamily ADUs

John owns a multifamily building with 17 apartment units. How many ADUs can he add?

On lots with multifamily dwellings, (2 or more units,) any number of ADUs are permitted within the existing building by converting existing space. Since the new ADUs shall comply with the State building standards for dwellings which has minimum facilities and size requirements, the actual number of attached ADUs depends on the size of the units, and the available existing area. Note that ceiling heights for R-1 (multi-family) occupancies is 7’-6”.

In addition, if there is space on the lot, John may also build up to two (2) detached ADUs.

ADU Permit Application Instructions 

Section 1 - Application Process

Steps to Getting a Building Permit for an ADU

  1. If the demolition of a garage/structure is required:
    • For a pre-1942 garage/structure apply for a Certificate of Approval from the Planning Division. Once approved, apply for a separate building demolition permit at the Permit Center.
    • If the garage/structure is not pre-1942, apply for a building demolition permit at the Permit Center.
  2. Apply for ADU permit from the Building Division at the Permit Center.
  3. If required, apply concurrently for solar, electrical main panel upgrade, new electrical meter and encroachment permits.
  4. Provide the completed ADU Zoning Checklist with your application.
  5. Junior ADUs Only: Record a Declaration of Restrictions at the Alameda County Recorder's Office.
  6. Begin construction once a permit is issued.
  7. Call for building inspections.
  8. Receive a Certificate of Occupancy.

What Happens During Review of an ADU Permit Application?

The Planning Division will review the design of the ADU to ensure that it complies with all zoning requirements such as size, height, location, and setbacks. The Building Division will review the plans for conformance with the California Residential Code/California Building Code. Applicants will be notified in writing (via a “Hold Notice”) if additional information or corrections to the plans are necessary or when the permit is ready to be issued. Other departments will review concurrently if Solar, Electrical and Encroachment permits are required.

Is Neighborhood Notification Required When Adding an ADU?

No, state law mandates ministerial review for all ADU applications so there is no public notification.

How Long Is the Permit Review for an ADU?

The length of building permit plan review depends on the quality and completeness of the plan drawing. If the initial submittal conforms to all building codes and requirements, the City review may be completed within 30 days. However, if the City finds that corrections and revisions are needed, the length of review may increase. Each round of review is a 30 day turnaround.

Section 2 - Application Materials

Documents Required at Time of Submittal

  • ADU Zoning Checklist
  • Plans of the proposed ADU (see Plan Drawings section below)
  • Certificate of Approval on first sheet of plans for demolition of pre-1942 garage/structure

Items Required for Junior ADUs Before Issuance of a Building Permit

  • Declaration of Restrictions (Deed Restriction) signed by the property owner(s) and notarized Copy of the property Legal Description (may be found attached to the Property Deed). Required for Junior ADUs only.
  • Bring the completed Declaration of Restrictions form and Legal Description to the Alameda County Clerk-Recorders Office for recordation. The hours and location of the County Clerk-Recorders Office may be found on their website.
  • To expedite processing, it is strongly recommended that a copy of the recorded Declaration of Restrictions is submitted along your application for a Building Permit.

Section 3 – Requirements for Plans and Drawings

General Requirements

  • Title Block: Address of Property, Owner, and Designer/Contact person with daytime phone number and email. APN.
  • Include Sheet Numbers.
  • Include North Arrow, date prepared, and bar scale. Acceptable scale: 1/4" or 1/8" = 1'.
  • All documents which are prepared by state licensed professional(s) shall be stamped and signed (including revisions) before issuance of permits.

List of Background Information

  • Scope of Work – Descriptive narration of the project.
  • State the estimated job valuation.
  • Owner's name, code information including code year, occupancy, and construction type.
  • Include a sheet index, zoning designation, and Assessor’s Parcel Number.
  • Show square footage (for each level) of existing living space, added living space and total.

Title 24 Energy Documentation

  • CF1R Energy forms to be printed on plans. Make certain all signatures are completed. The forms need to be readable so DO NOT reduce them in size.
  • All newly constructed, detached ADUs shall have a photovoltaic system. (This does not apply to existing structures being converted.)

Site Plan

  • Location of proposed ADU
  • Property lines, distance between outer edge of street curb and the front/street side property lines.
  • Lot size and dimensions.
  • Location and dimensions of all existing and proposed buildings.
  • Dimensions of existing and proposed front, side, and rear yards
  • Location and dimensions of existing and proposed driveways, garages, carports, required off-street parking spaces, and vehicle back-up areas
  • Location of all existing and proposed landscaping. Indicate any trees to be removed. Include circumferences of all trees. Provide species and common name of all trees.
  • Identify all permeable and non-permeable areas and square-footage.
  • For projects proposing construction within five (5) feet of property lines, plans must show the building footprints and appropriate height of structures on adjacent lots.
  • Location of drainage ways and access easements. Check with the Public Works Department for public utility and access easements. Private easements typically appear in the property legal description or title report.

Roof Plan

  • All existing and proposed roof elements
  • Label all roof pitches with slope

Elevations

  • Existing and proposed views of each elevation should appear side by side on the plans.
  • Fully label the elevations with dimensions.
  • Show/indicate all finishes, new and existing. Show all items such as windows, doors, decks, stairs, etc. Clearly distinguish what elements are existing and which will be added/changed.
  • Location of proposed vents, gutters, downspouts, air conditioning equipment, antennas, all rooftop mechanical equipment, utility meters, transformers, and utility boxes
  • Direction of building elevation (i.e., north, south, front, rear, etc.)
  • Details for fascia trim, windows, doors, trim, sills, railing and fencing, and final height of building
  • Location of exterior lighting and cut sheet/details of the type of lighting fixtures

Floor Plans

  • Fully dimensioned and prepared to an appropriate scale
  • Ceiling heights of all interior spaces
  • Label all rooms (existing and new). Show dimensions of all rooms
  • Clearly distinguish between new walls and walls to remain.
  • Show all walls with double lines. Clearly indicate fire/sound rated walls.
  • Show all windows and doors including sizes, types and egress windows. Show location of all existing and proposed windows and doors. Identify any opening within three (3’) feet of another building or property line.
  • Show all major equipment locations including water heater, HVAC, electrical panels, washer/dryers, plumbing fixtures, cabinets, etc.

Framing Plans

  • Provide for each floor and/or roof.
  • Show size, direction and spacing of all joists and beams.
  • Clearly show how any existing framing will be altered in order to meet current code requirements.

Construction Details and Sections

  • Drawn large enough to show the specific construction and referenced from framing plans.
  • Show major section through area of work including showing all major components.
  • Clearly indicate fire/sound rated assemblies.
  • Show ceiling heights. Show insulation including type & R-value.
  • Show stairways, fire/sound separation between units, moisture barrier under the floor slab, foundation wall waterproofing and drainage, etc.

Structural Calculations

  • Two (2) (unless otherwise directed) copies of structural design calculations and related details with signature of engineer in fresh ink on first page of each set of the calculations and all drawings directly related to the structural calculations.

Window Schedule (or Use City's standard Window Schedule) 

  • Numbered inventory list of existing and proposed windows
  • Label existing and proposed window types and dimensions
  • Show compliance for required egress windows for bedrooms
  • Show style of windows and materials on building plans or elevations
  • Cut sheets/brochures of proposed windows printed on the plans - include a dimensioned cross section of window, including exterior trim detail

Demolition Plan (If Applicable)

  • Label all rooms
  • Show items to be demolished as dashed
  • Clearly indicate which part of the structure is to remain
  • Written description of elements that will be removed and/or removed and reused materials

Foundation Plan (If Applicable)

  • Provide if the foundation will be replaced
  • Show dimensions – Provide details showing how existing or new foundations meet current code
  • Show hold downs and brace/shear wall locations and lengths
  • Indicate location and size of access openings
  • Show connections to existing & use detailing to show further information

Photographs Of:

  • Front, side, and rear elevations
  • Proposed work area
  • Printed on the plans and not as separate photos

Other Information

The City may request any other information relevant to the City’s review of an ADU project, including but not limited to, a property survey or title report

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