• accessory dwelling unit modern 250

ADU Calculator Can Help Homeowners Estimate Costs and Benefits of Building an ADU

Published:  July 10, 2019

The County of Sonoma is partnering 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.

Try the Sonoma/Napa Accessory Dwelling Unit Calculator  (Note: Calculator works in Firefox and Chrome)

Contact Information

Permit Sonoma
2550 Ventura Avenue
Hearing Room
Santa Rosa, CA 95403
38.465074, -122.723705

Get updates on Housing Initiatives

Accessory Units & Junior Units

Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) are an inexpensive way to create smaller, more affordable rental housing units.

ADU Calculator (beta)

Junior Unit

Try this new online tool to help estimate the costs, returns, and benefits associated with building an ADU.

Housing Initiatives

Permit Sonoma Housing Initiatives

Housing Initiatives

Permit Sonoma is introducing several initiatives to help meet the County's housing production goals.

Community Development Commission

Learn More

CDC Logo

The Community Development Commission (CDC) is dedicated to promoting decent and affordable housing, revitalizing communities, and supporting public services.

Office of Recovery and Resiliency


County Seal

Recovery-focused information on the County's efforts to build and rebuild housing