What are the issues I should be aware of if my property uses a septic system?

If you are on a septic system, it is important to ensure with your local agency that you have septic capacity to add an ADU or Junior ADU with your desired number of bedrooms before you move forward on plans for your project. Upgrading a septic system can be costly or challenging, and it is good to assess realistic needs upfront. Learn a ton more about septic systems from our detailed blog post on the topic right here. You can do so by reaching out to your local agency:

• For Sonoma County please contact Permit Sonoma Well & Septic at PermitSonoma-Well-Septic@sonoma-county.org or at (707) 565-2849.
• For Napa County please contact the Napa County Environmental Health Division at Environmental@countyofnapa.org or at (707) 253-4417.

If you don't currently have septic capacity for your ADU project and do not want to upgrade the system, ask your local planning department about the possibility of a "bedroom swap," which allows you to make construction changes to an existing bedroom in the primary residence to convert it to non-bedroom space (e.g., an office) and then use the newly freed up septic capacity for your ADU. Again, whether or not this is a possibility for you depends on your local jurisdiction and the specific details of your property.