California's 2020 ADU Rule Changes: What Property Owners Should Know
California took significant steps in 2017 with favorable Accessory Dwelling Unit (ADU) legislation, and a new series of state bills signed by Governor Newsom has continued that momentum. These changes further reduce barriers to building ADUs — also commonly referred to as granny flats, in-law suites, or backyard cottages. For anyone working with an ADU contractor or considering a project, here is a straightforward breakdown of what changed starting January 1, 2020.
Statewide Application: The 2020 ADU rule changes apply across all of California. Every local jurisdiction — cities, counties, and others — must comply. If a city does not create its own Accessory Dwelling Unit ordinance, state law applies by default. Any locally created ordinance must still meet the minimum standards set by the state.
Two ADUs Now Permitted on Single-Family Properties: Property owners are now allowed to add two ADUs to a single-family zoned lot — one full ADU and one Junior Accessory Dwelling Unit (JADU). A JADU is capped at 500 sq. ft. and must be created by converting part of an existing residence, such as a spare bedroom or an attached garage. This opens up more options for those looking for a JADU contractor or an in-law suite builder.
Larger ADUs Allowed: Between 2017 and 2020, many cities used local ordinances to restrict ADU size through lot coverage rules and other limitations. Under the 2020 rules, a detached ADU can be built up to 800 sq. ft. and 16 feet tall without requiring local discretionary approvals. ADUs created through conversions — such as a garage conversion — receive automatic approval. Where a local ordinance exists, it must permit ADUs of at least 850 sq. ft., or up to 1,000 sq. ft. for units with more than one bedroom.
Parking, Setbacks, and Structural Changes
Parking Exceptions Expanded: Parking requirements remain at one space per unit or per bedroom (whichever is less) for properties located more than half a mile from public transit. However, ADUs created within an existing structure — such as a garage conversion or carport — no longer require additional parking. Importantly, no replacement parking is required for the main residence when a garage or carport is demolished or converted by a garage conversion contractor.
Reduced Setbacks: Setbacks for new ADUs have been reduced to just 4 feet for side and rear yards, making it easier to fit a detached ADU builder's project on a typical lot.
Replace a Garage and Retain Setbacks: If an existing garage or carport is too costly to repair, state law now allows property owners to remove the structure and replace it with a new ADU that matches the original footprint — maintaining the existing reduced setbacks.
ADUs on Multi-Family Properties: Non-livable spaces within existing multi-family structures — such as storage rooms, garages, carports, mechanical rooms, attics, or basements — can now be converted into ADUs. At least one ADU can be added this way, up to 25% of the existing unit count. Additionally, up to two detached ADUs can be built on multi-family properties where land is available, subject to the 16-foot height limit and 4-foot setback rules.
Additional Provisions Worth Noting
- No Owner-Occupancy Requirements Until 2025: A five-year moratorium on owner-occupancy requirements means property owners can lease out both their primary home and their ADU simultaneously.
- Impact Fees: Cities cannot charge impact fees for ADUs under 750 sq. ft. For larger units, fees must be proportional to the ADU's size relative to the primary dwelling.
- Faster Approvals: Cities must provide approval or denial within 60 days of receiving an application when an existing single-family dwelling is on the lot — down from the previous 120-day window.
- HOA Restrictions Limited: Neither HOAs nor CC&Rs can reasonably prohibit the development of an ADU or JADU on a property.
- Legalizing Unpermitted ADUs: Property owners now have a 5-year window to bring unpermitted ADUs up to code, offering a path to compliance for existing structures.
Martins Construction Corp works within this regulatory framework, helping property owners navigate the ADU process — whether that involves a new detached ADU, a garage conversion, a casita, or a JADU. Understanding these rules is an important first step before beginning any accessory dwelling unit project.
