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Accessory Dwelling Unit Calculator

The County of Sonoma has partnered with local cities and the County of Napa to develop a regional Accessory Dwelling Unit Calculator to encourage our constituents to build accessory dwelling units (ADUs). This online tool helps individuals estimate the costs, returns, and benefits associated with building an ADU.

The Sonoma/Napa calculator is based on San Mateo County's Second Unit Calculator, and was developed by Baird + Driskell Community Planning with funding from ABAG/MTC, the California Department of Housing and Community Development, Community Foundation Sonoma County, and Napa Valley Community Foundation.

Find out more about Accessory Dwelling Units and whether your property meets the requirements to add a new ADU. If your property does meet the requirements for an ADU, enter your specific information into the calculator to get an estimate of what it would cost.

Use the ADU Calculator
(Note: Calculator works in Firefox and Chrome)

Contact Information

Contact Planning by Phone
Monday – Friday
10:00 AM – 12:00 PM
1:00 PM – 3:00 PM
2550 Ventura Avenue
Santa Rosa, CA 95403
38.465074, -122.723705


Accessory Dwelling Unit Regulations

Accessory Dwelling Unit Calculator
The ADU Calculator is a resource to help estimate the costs, returns, and benefits associated with building an ADU

ADU Rescue Program
Learn more on how you may qualify and apply for an ADU or JADU enforcement violation extension.

Napa Sonoma ADU Center
The Napa Sonoma ADU Center provides resources for homeowners in Napa and Sonoma counties who want to build an ADU.

Fire Prevention & ADUs

Fire Prevention Information on Accessory Dwelling Units

Fire Prevention and HazMat

Requirements for ADUs including fire access, sprinklers, and more.

Sonoma County Housing Authority

Resources for Property Owners

Hands forming house

If you plan to rent your ADU, consider participating in the Housing Authority's Housing Choice Voucher program and being a part of the solution to the County's affordable housing crisis.

State ADU Law

California Department of Housing and Community Development's web site describing state laws and regulations about Accessory Dwelling Units.

View State Web Site