SB 684 and the Starter Home Revitalization Act: What ADU Investors in OC and LA Need to Know
Most investors have heard of SB 9 — California's urban lot split law. Fewer have heard of SB 684. That's a mistake, because for property owners who want to add density without fighting City Hall, SB 684 may be the most powerful tool on the table right now.
Here's what it does, why it matters specifically if you own or are buying in Orange County or LA County, and how it interacts with ADUs in a way that most investors haven't worked out yet.
What SB 684 Actually Is
SB 684 (2023) amended the Starter Home Revitalization Act (SHRA) — a state law that creates a ministerial approval pathway for subdividing a single property into up to 10 parcels, each with its own residential unit.
The updates from SB 684 took effect July 1, 2024. Since then, the law has been expanded further by SB 1123 (2024) and AB 130 (2025), both effective July 1, 2025. Together, these amendments represent the most significant loosening of the subdivision approval process in California in decades.
What "ministerial" means in practice: no discretionary review, no public hearing, no CEQA, no right to appeal. The city reviews your application against objective standards only — think heights, setbacks, lot size minimums — and must approve or deny within 60 days of receiving a complete application. If they miss the deadline, the application is deemed approved by operation of law. That's the same protection SB 9 projects gained through SB 450 — applied now to a pathway that allows up to 10 units instead of two.
For investors who have dealt with LA City's planning counter or who've watched a project sit in discretionary review for 18 months, that 60-day hard cap is not a small thing.
The Eligibility Basics
Before you get excited about a specific property, you need to check the eligibility criteria. The California HCD's ADU and housing law guidance is the authoritative source on how these state laws interact — but here's the summary version:
Site size: Multifamily-zoned lots must be under 5 acres. Single-family zoned lots must be under 1.5 acres and vacant (no permanent structure, or existing structure is abandoned and uninhabitable).
Maximum subdivision: Up to 10 new parcels and 10 residential units. ADUs and JADUs are excluded from both counts. More on this in a moment.
Minimum parcel sizes after subdivision: 600 sq ft in multifamily zones, 1,200 sq ft in single-family zones. These minimums are tiny. They're intentionally small to allow the maximum number of units the law permits.
Surrounding context: The site must be substantially surrounded by qualified urban uses. Properties in prime farmland, wetlands, high fire hazard severity zones, habitat for protected species, or lands under conservation easements are not eligible.
Demolition protections: You can't use SB 684 on a property where a tenant has lived within the last five years, where rent-controlled or covenant-restricted affordable units exist, or where an Ellis Act withdrawal occurred within 15 years. These protections are real and enforced — check ZIMAS before you assume a property qualifies.
The Objective Standards That Get Waived
Here's where the law gets interesting for investors. SHRA projects aren't just approved faster — several local restrictions simply don't apply.
Density limits: Local zoning density caps can't be used to prohibit what the SHRA's parcel size minimums allow. HCD's Technical Assistance letters to Oakland and Morro Bay have confirmed this explicitly. If the math works at 600 sq ft per parcel in a multifamily zone, you can build to that density whether or not local zoning would normally permit it.
Building separation requirements: No zoning setbacks or building separation requirements between units may be enforced — including the passageway requirements that normally apply under the LA Municipal Code. Units can be built right next to each other (California Building Code fire separation requirements still apply, but local setback rules between units do not).
Side and rear setbacks from original lot lines: Local agencies can't require setbacks greater than four feet from the original side or rear property lines.
Parking: No more than one parking space per unit can be required. And if the site is within half a mile of a high-quality transit corridor or major transit stop, zero on-site parking can be required at all. In a city like Long Beach or parts of LA, that's a lot of properties where parking requirements evaporate entirely.
Floor area ratio (FAR) floors: Local agencies can't impose a FAR below 1.0 for 3–7 unit projects, or below 1.25 for 8–10 unit projects. In single-family zones where local zoning might cap FAR at 0.45 or 0.65 (think the BMO in LA City), the SHRA overrides that.
Minimum lot size, width, frontage, and depth: Beyond the SHRA's own minimums, the city can't impose any of these. The standard 20-foot frontage requirement in LA's definition of a "Lot"? Gone for SHRA projects.
The ADU Angle — And Why It Changes the Math Completely
Here's the detail most people miss: ADUs and JADUs are excluded from the SHRA's 10-unit cap.
That means on a qualifying lot, you can potentially build up to 10 primary residential units through the SHRA subdivision process — and then add ADUs on top of those. This is the same stacking logic that makes buying multi-unit properties in LA County and then adding ADUs such a compelling strategy right now — except with SB 684, you're creating the multi-unit structure from scratch on a single parcel.
In LA City's implementation, the rules work like this: in fee-simple SHRA projects (individually owned lots), one attached ADU or JADU is allowed on each newly created parcel. In multi-family SHRA projects, all normally applicable provisions of California's state ADU law apply.
So the income stack on a correctly structured SHRA project looks like this: start with the maximum number of primary units the site can support. Add ADUs where eligible. The result is a unit count that would have been impossible — or required years of discretionary entitlements — before this law existed. That kind of density is exactly what drives the income-approach valuations that make multi-unit ADU properties so valuable at sale.
Stacking SHRA With the State Density Bonus
SHRA projects can be filed concurrently with a State Density Bonus application. If you're providing affordable units and want to push unit count above what the SHRA alone allows, these programs run in parallel — with no public hearings required under either. The density bonus calculation uses the greatest number of units allowed by local zoning or the general plan, not the SHRA's density — so the two programs don't cannibalize each other.
What This Looks Like in Practice for OC and LA Investors
The SHRA is a statewide law. The detailed implementation memo is LA City's — but the law applies throughout California, including OC cities like Anaheim, Garden Grove, Long Beach, and Costa Mesa.
For an investor looking at a qualifying multifamily lot today, the path looks like this:
Check ZIMAS (in LA) or your city's equivalent eligibility tools to confirm the site qualifies. In LA, the SHRA Eligibility Criteria Checklist lives under the "Planning and Zoning" tab at zimas.lacity.org.
Submit a parcel map or tentative tract map application with the housing development concurrently.
The city has 60 days to approve or deny — and can't require a hearing or CEQA review.
Get your early-start building permits once the tentative map is approved (you don't have to wait for final map recordation to start building).
Stack ADUs on each fee-simple parcel where eligible.
The financing side also shifts once units are in place and generating documented rent. That documented rental income changes how lenders look at you — both for refinancing the original acquisition and for qualifying on your next purchase. If your personal income isn't the right vehicle for qualification, DSCR loans underwrite the property's cash flow directly — which is exactly the structure a stabilized SHRA project is built for.
What to Watch Out For
The SHRA is powerful, but it's not a blank check.
Demolition protections are strict. If there's been a tenant in the building within the last five years — including housing that was demolished and tenants who vacated — the site doesn't qualify. LA City is reviewing multifamily building permits issued since January 2023 to verify compliance. This is one of the things I check before any offer goes in, and it's covered in the pre-offer due diligence framework I run on every investment property in OC and LA.
Housing Element sites have minimum density requirements. If your target parcel is listed in the City's 2021–2029 Housing Element, you must build at least as many units as the City projected for that site. If the site was identified to accommodate lower-income RHNA units, you have to include those too.
The 60-day clock starts on a complete application — meaning complete including payment of all fees. An incomplete notice from the city resets the clock. The more airtight your application, the harder it is for a city to toll the timeline.
Single-family zone height requests require extra justification. While height limits are generally preempted when they conflict with the protected density rules, LA City retains discretion to deny height relief requests in single-family zones specifically. This is one area where the SHRA doesn't offer complete protection.
The Bottom Line
SB 684 and the Starter Home Revitalization Act represent the most meaningful shift in California subdivision law in a generation. The 60-day ministerial approval pathway, the elimination of hearing rights and CEQA, and the removal of most standard setback, parking, density, and FAR requirements — stacked on top of the ADU law — create a unit-addition pathway that investors in LA and OC should be running the numbers on now, not after the next round of regulatory changes.
The three wealth-building levers that run simultaneously on Southern California income property — cash flow, principal paydown, and appreciation — all get compressed into a single parcel when the SHRA math works. The investors building the strongest income positions in markets like Anaheim, Garden Grove, and Long Beach right now are not finding bigger lots. They're finding the right lots — and understanding which laws give them the maximum development potential on those lots before they write the offer.
If you're looking at a specific property and want to understand what the SHRA, SB 9, and the ADU law actually allow on that parcel, that's exactly the kind of pre-offer analysis that separates a good deal from a great one.
Dylan Serna | ADU Specialist | DRE #02217359 Call or text: (714) 860-2868 | adurealtor.net | Book a Strategy Session
