California has rewritten its ADU law almost every year since 2017, and the result is one of the most homeowner-friendly sets of rules in the country. It is also scattered across a dozen bills, renumbered into a new part of the Government Code in 2025, and amended again for 2026. Most homeowners only need to know a handful of it.
This guide covers what the state guarantees every homeowner, what changed for 2026, and where local rules in Monterey County still shape what you can build. Code sections are given so you, or your designer, can check them.
What California ADU Law Guarantees
State law sets a floor. Cities and counties can be more permissive than these rules, but not more restrictive. If your property allows a single-family or multifamily home, the following apply:
| Rule | What the state guarantees | Government Code |
|---|---|---|
| Minimum size allowed | Every jurisdiction must allow at least an 800 sq ft ADU with 4-foot side and rear setbacks, regardless of lot coverage or floor-area limits | § 66321(b)(3) |
| Setbacks | No more than 4 feet from side and rear lot lines for a detached ADU | § 66321(b)(3) |
| Height | 16 ft detached; 18 ft near major transit or with a multistory multifamily building (plus 2 ft for roof pitch near transit); 25 ft or the zone limit for attached ADUs | § 66321(b)(4) |
| Approval time | Approve or deny within 60 days of a complete application | § 66317(a)(3) |
| Impact fees | None for ADUs under 750 sq ft; proportional to the main house above that | § 66311.5(c)(1) |
| Replacement parking | Not required when a garage or carport is demolished or converted for an ADU | § 66314(d)(11) |
| Fire sprinklers | Not required unless required for the primary residence | § 66314(d)(12) |
| Owner occupancy | Not required for ADUs | § 66315 |
| Junior ADU | Up to 500 sq ft, entirely within a single-family home | § 66313(d) |
Source: California Department of Housing and Community Development, ADU Handbook (March 2026 update).
Two of these do the most work in practice. The 800-square-foot guarantee means a local rule like a lot-coverage cap or floor-area ratio cannot be used to block a modest ADU. And the 60-day clock means the review is ministerial: if the plans meet the objective standards, the application is approved without a hearing.
What Changed for 2026
Several bills signed in 2025 are now in effect; most took effect on January 1, 2026, and AB 462 in October 2025. The ones that matter to a homeowner on the Central Coast:
- SB 543: faster completeness, clearer sizing. A local agency now has 15 days to tell you whether your application is complete; if it doesn’t, the application is deemed complete. The bill also clarifies that the 800-square-foot guarantee refers to interior livable space, and exempts ADUs and JADUs under 500 square feet from school impact fees.
- AB 462: a 60-day clock for coastal permits. ADUs in the Coastal Zone have long been slowed by the Coastal Development Permit, which sat outside the 60-day rule. AB 462 requires those coastal permits to be approved or denied within 60 days or be deemed approved. For coastal parcels in Monterey, Carmel, Pacific Grove and Pebble Beach, this is the biggest change of the year.
- AB 1154: narrower owner-occupancy for JADUs. The owner-occupancy requirement now applies only to a junior ADU that shares bathroom facilities with the main house. A JADU with its own bathroom no longer carries it.
- Stronger enforcement. 2025 legislation gave the state more power over local ordinances that do not comply with ADU law, including treating non-compliant ordinances as void when a local agency fails to correct them.
Laws already in force that are still worth knowing: AB 976 permanently removed owner-occupancy requirements for ADUs; AB 1332 requires local agencies to offer pre-approved ADU plans; SB 1211 expanded detached ADUs on multifamily lots to as many as eight; and AB 2533 created a path to legalize unpermitted ADUs and JADUs built before January 1, 2020.
One administrative change explains why older articles cite different section numbers. In 2025 the state reorganized its ADU law into Government Code sections 66310 through 66342. The rules mostly carried over, but the old section 65852.2 references are out of date.
What Monterey County and Local Cities Add
State law sets the minimums. Local ordinances fill in the rest, and on the Monterey Peninsula they differ meaningfully from one jurisdiction to the next.
- Unincorporated Monterey County has separate rules for inland and coastal areas. In the Coastal Zone, a Coastal Administrative Permit is required. The county offers pre-approved ADU plans: three floor plans (515, 749 and 1,200 gross square feet) in two styles, designed for slab-on-grade foundations. Sites that do not suit a slab need an individual soils report, and changes beyond the offered options send the plan back through review as a custom ADU.
- City of Monterey caps attached and detached ADUs at 850 square feet for a studio or one-bedroom and 1,000 square feet for more than one bedroom, with a 500-square-foot JADU limit (section 38-112.6). Those caps sit above the state’s 800-square-foot floor.
- Carmel, Pacific Grove and Pebble Beach each apply their own ordinance on top of state law, along with design review, historic resource and coastal considerations that can shape what gets approved.
The practical lesson: state law tells you that you can build an ADU. The local ordinance, your zoning and whether you are in the Coastal Zone tell you what it will look like and how long it will take.
What State ADU Law Does Not Do
A few common misunderstandings:
- It does not waive the building code. An ADU still needs a building permit and has to meet the California Building Standards Code, including structural, fire and Title 24 energy requirements. The 2025 code edition took effect on January 1, 2026.
- It does not override every local standard. Objective local standards that do not conflict with state law still apply, including design standards in many jurisdictions.
- It does not let you skip coastal review. AB 462 speeds the coastal permit up; it does not remove it.
- It does not legalize everything already built. AB 2533 covers ADUs and JADUs built before 2020. Other unpermitted work goes through the normal permit process. See what happens if you build without a permit.
Where to Start
If you are new to the terms, what qualifies as an ADU in California and granny flat vs. ADU cover the basics. For size, see the ADU size guide; for plans, see ADU plans in California.
Renovation Drafting & Design prepares permit-ready ADU drawings and handles the permitting path, including coastal parcels, across Monterey, Carmel, Pacific Grove, Pebble Beach and Carmel Valley. See our ADU design service or get in touch.
This is a summary of state and local rules at the time of writing, not legal advice. ADU law is amended frequently; confirm current requirements with your local planning department.
Building in Monterey County? Our step-by-step guide covers who reviews the permit, the site checks to do first, the County’s pre-approved plans and the 60-day clock: how to build an ADU in Monterey County.
California ADU Law FAQs
What are the new ADU laws in California for 2026?
The main changes are SB 543, which gives local agencies 15 days to determine whether an ADU application is complete and exempts units under 500 square feet from school impact fees; AB 462, which requires Coastal Development Permits for ADUs to be decided within 60 days; and AB 1154, which limits JADU owner-occupancy requirements to units that share a bathroom with the main house.
How big an ADU does California law allow?
Every jurisdiction must allow at least an 800-square-foot ADU with 4-foot side and rear setbacks. Local ordinances can allow larger units; the City of Monterey, for example, allows up to 850 square feet for a studio or one-bedroom and 1,000 square feet for more than one bedroom. A junior ADU is limited to 500 square feet.
How long does a city have to approve an ADU in California?
Sixty days from receiving a complete application. Since 2026, the agency also has 15 days to say whether the application is complete, or it is deemed complete.
Do I have to live on the property to build an ADU in California?
No. Owner-occupancy requirements for ADUs were permanently removed. For junior ADUs, owner occupancy now applies only when the JADU shares bathroom facilities with the main house.
Are ADUs exempt from impact fees in California?
ADUs under 750 square feet are exempt from impact fees. Above 750 square feet, fees are charged in proportion to the size of the ADU relative to the main house. Since 2026, ADUs and JADUs under 500 square feet are also exempt from school impact fees.
Do ADUs in the Coastal Zone follow the same rules?
They follow the same state ADU rules but also need a coastal permit. Under AB 462, Coastal Development Permits for ADUs must now be approved or denied within 60 days or they are deemed approved. In unincorporated Monterey County, coastal ADUs require a Coastal Administrative Permit.