Accessory Dwelling Units - ADUs

Accessory Dwelling Unit (ADU) 

Land Use Code Requirements and Development Impact Fee Reductions
Effective June 19, 2019

Updated December 17, 2019


Download a PDF brochure of this ADU information

What is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling unit is a dwelling unit for rental or occupancy that is attached to or detached from a primary single-family residence and located on the same parcel. An ADU must have sanitary and cooking facilities and comply with specific standards, as listed below. See the City’s adopted ADU Ordinance, Section 20.20.010 of the Land Use Code, for additional information. 

Another type of ADU is a Junior Accessory Dwelling Unit (JADU), which is a unit that is no more than 500 square feet in size and contained entirely within a legally permitted single-family dwelling, and uses an existing bedroom and contains an efficiency kitchen. A JADU may include separate sanitation facilities, or may share sanitation facilities with the existing structure.

Why build an ADU?

There are many reasons for building an ADU on your lot. ADUs can provide additional space for caregivers, grown children, elderly parents, or renters. ADUs allow for an opportunity to produce additional household income through renting the ADU or primary residence. “Empty nesters” can stay in their neighborhood by moving into a smaller ADU and renting their existing home to pay for the mortgage and/or to provide additional income. An ADU can be built to house a relative or caregiver.

Where can an ADU be built?

  • ADUs can be built in any zoning district that allows and contains single-family housing. An ADU can also be built on any lot that has an existing legally permitted single-family house.
  • ADUs can either be attached to or detached from a single-family house or through the conversion of existing floor area.
  • ADUs are typically subordinate in size to a single-family house and located on the same lot.

What are the use and occupancy restrictions for an ADU?

  • ADUs must be rented for terms more than 30 days for residential purposes.
  • ADUs cannot be used as a short-term or vacation rental (fewer than 30 days).
  • A property owner is not required to live on-site.
  • A deed restriction must be recorded against the parcel identifying the limitations on use, size and sale of the ADU.  A sample deed restriction is available on the ADU webpage at: Sample Deed Restriction

What types of houses can be an ADU?

ADUs may be of standard residential construction, manufactured housing or factory-built housing on permanent foundations. Manufactured or prefabricated homes may provide a more cost-efficient means to add an ADU to your site. There are various vendors in the Bay Area and Northern California. Also, consider if your site is located in a designated historic district or with “Character Area 1” in the Citywide Design Guidelines. In these cases, it will be important to adjust the roof and exterior materials of the proposed manufactured or prefabricated home. 

What are the requirements?

An Accessory Dwelling Unit may be created through the conversion of existing floor space, such as an existing bedroom for a JADU or an attached or detached garage to create a new ADU on the site. ADUs may also be created through additions to the existing home or detached garage or through new construction on the site. The City’s municipal code provides development standards for both conditions (conversion of floor area and new construction/additions), as noted in the following table.

Development Standards Table

How do I find my zoning information?

Zoning Designation. The City adopted a zoning map, which designates the zoning districts throughout the City. View the City’s zoning map here: Zoning Map

Zoning District Development Standards. Zoning district information regarding applicable setbacks and site coverage may be found in the “Land Use” code section of the City of Healdsburg Municipal Code. Typically, these requirements are located in the “Minimum Development Standards” under each zoning district. View the zoning district information here: Land Use Code Zoning Districts 

How is the size of an ADU calculated?

Detached ADUs. Floor area is measured from the outside of the exterior walls of the ADU. Proposed habitable space located under a sloping roof where the sloping ceiling measures less than five feet from the finished floor to the finished ceiling is not counted as floor area.

Attached ADUs. Floor area is measured from the outside of the exterior walls of the ADU to the centerline of shared interior walls that separate the accessory unit and primary-unit living space. Proposed habitable space under a sloping roof where the sloping ceiling measures less than five feet from the finished floor to the finished ceiling is not counted as floor area.

Excluded Areas. Carports, covered porches (open on three sides) and patios, chimneys, stairwells and mechanical closets are not counted toward the determination of floor area of the Accessory Dwelling Unit.

What design elements are applicable to ADUs?

The City’s land-use code includes specific design criteria that apply to ADUs regarding placement, compatibility, parking locations, and entrances. Compliance with these design criteria will need to be documented through your building permit submittal as part of the site plan, elevations, proposed materials and photographs. The design criteria include the following:

Placement. Detached and attached ADUs (and all associated outdoor living areas and accessory structures) shall comply with the setback requirements of the zoning district in which the ADU is to be located.  An attached or detached ADU shall not be placed between a required front yard setback from a public right-of-way and the primary dwelling unit.

Compatibility. An Accessory Dwelling Unit shall be compatible with the existing primary dwelling unit  and shall include the same roof slope and material, exterior wall colors, architecture, and landscape design. This is particularly important in identified historic districts and “Character Area 1” and  the “Historic District (HD) Overlay” as identified in the Citywide design guidelines. Flexibility in design compatibility may occur in other areas of the City dependent on the quality of the materials and location of the ADU.  

Entrance. A separate entrance to an ADU shall be provided and access to the public right-of-way may be provided through the rear yard of the primary residence or a dedicated pathway. The City’s design guidelines are available on the City’s website at the link below. The design guidelines can provide additional guidance when considering an addition or new construction for an ADU.

What else should I keep in mind when designing my ADU?

Fire Safety Requirements. The overall size and location of an ADU and available water pressure affect applicable fire code requirements such as fire sprinklers, water supply upgrades or fire hydrant upgrades. These factors include the following:

  • Structure Size: The total size of the proposed structure will be factored into determining applicable Fire Code requirements. For example, a 600 square-foot ADU over a 700 square-foot three-car garage would be counted as a 1,300 square feet structure. Generally, new structures over 1,200 square feet will require fire sprinklers. Additionally, for remodels and ADU additions, the area of the remodel and size of the ADU addition will be considered in determining if fire sprinklers are required. Generally, the threshold is a remodel and/or addition exceeding 50% of the existing home (this calculation is done by Fire Department Staff).
  • ADU Location and Water Pressure: The proximity of a new ADU structure to fire hydrants, the public right-of-way, and water pressure (fire flow) are also factors in determining fire-safety requirements.

The Healdsburg Fire Department evaluates these factors when a building permit is submitted for review. For more information, please contact the Fire Department at (707) 431-3360.

What City permits and fees apply?

Building Permit.  A building permit is required for all ADUs, including conversion of existing living space or garage area. Building fees are based on the valuation of the ADU construction costs. Contact the City’s Planning and Building Department for more information at (707) 431-3346. 

Fire Sprinkler Permit. Additions and new construction requiring fire sprinklers will need separate plans to be submitted for fire sprinkler design to the Fire Department. Please contact the Fire Department at (707) 431-3360 for more information.

School Impact Fees. Additions or new construction over 500 square feet may be subject to school district fees. Currently, the fees are $2.97 per square foot or $5.25 per square foot if located in “Sub Area A” (per the Healdsburg General Plan). Please contact the Healdsburg Unified School District business office at (707) 431-3403 or visit the HUSD Website for more information.

Development Impact Fees. Impact fees are also required for a new ADU at a rate of half of the single-family rate. *contact staff for confirmation of current fees.Development Fee Table

How can I get more information?

Call. Planning and Building Staff are available to answer questions at the Community Development Center at (707) 431-3346.

One-Stop Assistance Center.  If you are considering an ADU on your property, you can receive personalized information and guidance through the City’s One-Stop Assistance Center. One-Stop meetings are held on Thursday afternoons, at no cost, and staffed by members of the Planning, Building, Public Works, and Fire Departments to answer all your questions regarding ADU development. To schedule an appointment for a One-Stop meeting, please call the Community Development Center at (707) 431-3346.

Lot Size.  To find  your lot size, you may contact the Planning Division at the Community Development Center or you may try the Sonoma County Assessor Office website. 

Site Zoning. To find  your site zoning, you may contact the Planning Division at the Community Development Center or you may view the City of Healdsburg’s zoning map at the  following link: 

Site Zoning Development Standards. To find the maximum site coverage and setback requirements (for additions to existing  homes), you may view the City of Healdsburg’s zoning district information in the Land Use Code.  

How do I get started?

Understand Your Zoning Requirements. First, figure out your lot size, site zoning and development standards including your maximum site coverage.

Determine Your Allowed and Available Site Coverage. Second, figure out your remaining site coverage by calculating the existing floor area for the first floor of all structures located on the site. Next, multiply your maximum site coverage percentage by the lot size in square feet. This calculation is the maximum site coverage in square feet for your site. Last, subtract the existing site coverage from the allowed maximum site coverage.

Determine Your ADU Type and Size. Once you have determined the remaining site coverage on your site, determine the type and size of the unit that you want to add to the site.

Sketch it Out. A sample site plan has been provided for reference in addition to blank graph paper for you to sketch out your project. When sketching your project, determine the size of each square based on your lot size. Indicate adjacent streets, existing building footprints with dimensions and north arrow. Next, draw in the location and dimensions of the proposed ADU addition or new structure. Use the sample site plan and graph paper to start your project. For more questions follow up with Planning Division Staff at the Community Development Center.


Napa Sonoma ADU Center - The Community Foundation Sonoma County and the Napa Valley Community Foundation have partnered with jurisdictions in Napa and Sonoma Counties to promote accessory dwelling units.  Their website provides many useful tools for all stages of building ADUs.

Center Sponsored Webinars:  

Manufactured/Prefabricated Housing websites. The following links have been provided for your reference and the City does not endorse any specific vendor. Please do y our research and ask questions of the company and City Staff. 


Adopted Documents

City Council Review
The Healdsburg City Council conducted public meetings on May 6 and May 20 of 2019 to take public comments and approve proposed changes regarding ADU impact fees and changes to the Healdsburg Municipal Code. The City Council staff report and attachments are available below:

Planning Commission Review
The Planning Commission held a public hearing on April 9, 2019, to consider proposed changes to the existing Accessory Dwelling Unit Ordinance. The Planning Commission considered changes to increase the maximum ADU size, site coverage requirements, parking requirements for garage conversions and reorganization to make the code more user friendly. The Planning Commission staff report and associated attachments are available at the link below.