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)