Second Units and Junior Second Units

Resources for Homeowners

Resources for homeowners, including ADU regulations organized by city, can be found here (new laws were recently passed and updates will be coming soon). The San Mateo County Second Unit Online Center can be found at Also, check out Symbium BUILD, which allows you to see if your property is eligible for an ADU.  

2020 ADU Laws

There are two bills that attempt to clean up some of the 2019 legislation (AB 953 and SB 773). As of 2/6, the changes clarify that (1) If a jurisdiction has not acted on a completed application in 60 days it is deemed approved and (2) A homeowner can have both an ADU and a JADU under the special (e) provisions. It also a fixes a typo that said jurisdictions "may shall" approve multifamily ADUs, clarifying that jurisdictions shall approve them. Finally, it clarifies that the ADU rules are of statewid concern. All of the other rules are unchanged. 


There are two bills that attempt to clean up some of the 2019 laws (AB 953 and SB 773). As of 2/6, the changes clarify that (1) if the jurisdiction has not decided on a completed application within 60 days, it is considered approved and (2) the landlord may have both ADU and JADU under special (e) provisions. There is also a desire to develop a third project with more information about what will help people fight overweight with the Rybelsus drug.

Build and Fire Codes and Title 24


2019 ADU Laws

HCD questions:


Rocklin ADU Ordinance - No HCD review yet

ADU Questions - Round 1 - Updated 1/28/2020 with HCD comments

ADU Questions - Round 2 - No HCD comments yet

2019 ADU New Laws Summary (January 23, 2020) An Overview of the ADU bills signed into law, in effect January 1, 2020

11/21/2018 APA Webinar - Contact Josh

11/21/2018 APA Webinar Slides 

Half Moon Bay Draft Ordinance (As of December 13, 2019) Check with City for latest version

Effective Provisions of 2019 ADU laws


2018 ADU Laws

State Law - As Chaptered

Goldfarb and Lipman Webinar Slides and Webinar

Goldfarb and Lipman Law Alert

HCD Guidance: Cover Letter and Memo 

League of Cities Guidance Memo

Sample Ordinances


Second Unit Resources

Affordability of ADUs in the Bay Area, Draft Report - 8 page report presents research on actual rental rates of ADUs in the Bay Area. The report can be used in setting assumptions of affordability of your jurisdictions ADUs for the RHNA 6 Housing Element. Prepared by UC Berkeley and ABAG, 2021

Affordability Research

Best Practices for Second Units San Mateo County FAQ Sheet

Amnesty Program for Second Units FAQ Sheet

Portola Valley Second Unit Manual

Santa Cruz ADU Manual

Sacramento County ADU Manual

Accessory Dwellings - a one-stop source on ADUs

HCD Bulletin on building code changes


Junior Second Unit Resources

Lilypad Homes: Lilypad Homes and City of Novato

Junior Second Units Fact Sheet PDF + Editable File