Resource · California ADU Law

What California ADU Law Allows on Your Specific Lafayette Lot

AB 68, AB 881, SB 9, and SB 13 — translated into what they actually mean for your parcel’s size, slope, and setbacks. Read this before you hire anyone.

RBy Shay Zilber, CEO · Rhino Builders · CSLB #580756 · Lafayette, CA

What California ADU Law Actually Says — and What It Allows on Your Lot

Four state laws — AB 68, AB 881, SB 9, and SB 13 — reshaped ADU construction across California between 2020 and 2022. They eliminated many local restrictions, reduced setbacks, removed fee burdens on smaller units, and allowed more density on single-family lots than California had permitted in decades. But state law describes what’s allowed in general.

Your Lafayette parcel has specific dimensions, a specific slope, a specific zone designation, and a specific relationship to surrounding lots. Those conditions determine what the law actually permits — on your property, not someone else’s. This page maps each of the four major laws to the parcel conditions they interact with in Lafayette.

Why Homeowners Reading the Same Law Reach Different Conclusions

California ADU law was written at the state level and applies uniformly — but the parcels it applies to aren’t uniform. A homeowner in Sacramento reading AB 68 and a homeowner on a hillside lot off Deer Hill Road are reading the same statute; their buildable envelopes under it are not the same. Lafayette’s hillside parcels commonly carry steeper grades, fire-zone overlays, and soil classifications that affect where structures can sit and what engineering they require.

The soil behavior that shapes ADU siting and foundation design across Lafayette's hillside corridors is documented in detail on our hillside lot construction resource.

A four-foot setback on a flat lot is a four-foot clearance to the property line. On a sloped lot, it’s a four-foot clearance measured at grade on the downhill side — which can mean something very different about where your ADU can physically sit. Contra Costa County interprets state ADU law in the context of those local conditions.

The Four Laws That Changed What Lafayette Homeowners Can Build

1AB 68 — Setbacks & Minimum Lot Size (2020)4-ft setback

Standardized ADU setbacks statewide, overriding local rules that often required ten feet or more. Detached ADUs are now permitted with a four-foot rear and side setback on most residential lots, and AB 68 eliminated minimum-lot-size rules that let jurisdictions block ADUs on smaller parcels. On your lot: if you have a usable rear or side yard, the four-foot rule likely gives you more buildable space than local zoning allowed — the question is whether that space, after coverage, slope, and fire-zone restrictions, supports the unit size you want.

2AB 881 — Owner-Occupancy Removed (2020)Through Jan 2025*

The companion bill to AB 68 suspended the owner-occupancy requirement — the condition that the owner occupy either the primary dwelling or the ADU — through January 1, 2025, opening ADU construction for investment. On your lot: homeowners who planned to rent both units simultaneously had that option through January 2025. *If your timeline extends past that date, or you're reading this after 2025, verify the current status of the owner-occupancy rule at the time of your permit application — this is one of the provisions most likely to have changed.

3SB 9 — Lot Splits & Additional Units (2022)Up to 4 units

Permits most single-family lots to be subdivided into two parcels and allows up to two primary dwellings per parcel — creating the legal potential for four units when combined with ADU rights. It applies to Lafayette single-family zones subject to parcel-size and configuration rules; lots in historic districts, certain hazard zones, or below minimum post-split size may not qualify. On your lot: a parcel that reads SB 9-eligible on zoning alone can be disqualified by slope, fire-zone designation, or configuration once the full analysis is applied.

4SB 13 — Fee Waivers for Smaller ADUs (2020)Under 750 sq ft

Eliminated impact fees — development charges that can add tens of thousands — for ADUs under 750 sq ft, and requires proportional fees for larger units relative to the primary dwelling. Note: the waiver applies to impact fees only; Contra Costa County permit fees and utility connection fees are not covered and apply regardless of size. On your lot: an ADU under 750 sq ft directly reduces project cost; for a larger unit, run the proportional-fee calculation before finalizing your budget.

How These Laws Play Out on Real Lafayette Parcels

The same law produces different project realities depending on which lot it’s applied to:

Flat · Burton Valley

9,000 sq ft · Moderate zone

AB 68's four-foot setback gives usable rear yard; lot coverage can't be used to deny an ADU of 800 sq ft or smaller; SB 13 waives impact fees under 750 sq ft. More flexibility than the hillside neighbor reading the same law.

Hillside · Above Downtown

6,500 sq ft · 12% slope · High zone

AB 68 permits the ADU, but slope reduces the buildable rear yard, a geotechnical report is required, the building-pad location drives the design, and roofing and venting must meet Chapter 7A for a High designation. None of that appears in the text of AB 68.

SB 9 Split?

12,000 sq ft · single-family

Zoning reads SB 9-eligible, but a rear-yard creek setback from a seasonal drainage easement drops the effective second parcel under minimum post-split size — so SB 9 doesn't apply. ADU rights under AB 68 remain; the subdivision pathway doesn't.

How Rhino Reads These Laws Against a Specific Lafayette Lot

Reading state ADU law and applying it to a real parcel are two completely different tasks.

Shay Zilber · CEO, Rhino Builders

We were operating when AB 68, AB 881, SB 9, and SB 13 all moved through the legislature into active permit requirements. Here’s what 37 years of permit history gives you that reading the statute doesn’t: the county interprets these laws through the lens of the plans in front of them. AB 68 allows a four-foot setback — but if a fire-zone overlay requires additional defensible-space clearance, or a drainage easement runs along the rear property line, the effective setback the plan checker approves is whatever four feet becomes after those conditions apply. We map every one of these laws to the actual parcel before any design starts, because a plan that ignores those conditions doesn’t survive the first plan check.

When to Get a Parcel-Specific Assessment Before Design Starts

Reading state ADU law is a reasonable first step — understanding what AB 68 changed, what SB 13 waives, and what SB 9 allows gives you a working foundation. The point where reading ends and application begins is where you need someone who has submitted permit packages to Contra Costa County under these laws and received approvals. Mapping the legislation to your lot’s specific conditions — slope, zone, soil, coverage, easements — before design eliminates the correction-letter cycle that adds months.

If you’re on a hillside lot, in a High or Very High fire zone, or considering SB 9 subdivision, parcel-specific analysis isn’t optional — the variables interact in ways the statute text doesn’t describe. And this legislation continues to evolve: provisions like the owner-occupancy suspension have expiration dates built in, so verify the current status of any time-sensitive provision before filing.

Areas We Serve

Rhino Builders serves Lafayette and the full San Francisco Bay Area — building across Contra Costa County including Lafayette, Orinda, Pleasant Hill, Walnut Creek, Oakland, and surrounding communities, from our office at 3685 Mount Diablo Blvd #161.

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Map California ADU Law to Your Lafayette Lot

The four laws define what California permits; your parcel determines what actually gets built. Bring your lot dimensions, address, and whatever you’re considering — we’ll tell you what the law allows on your specific property, not in general.