Why SB 9 Lots in Los Angeles City Are a Different Beast — ZA Memo 143 Removes the Size Ceiling on Your ADU
Most investors shopping for ADU properties in LA County treat SB 9 lots like a footnote — a nice-to-have zoning detail that gives you an extra unit. That's a mistake. In the City of Los Angeles specifically, SB 9 lots carry a structural advantage that almost nobody talks about: when you combine an SB 9 Two-Unit Development with the City's own Zoning Administrator's Memorandum No. 143 (ZA Memo 143), the city's residential floor area (RFA) limits — the same limits that cap how big you can build on almost every R1 lot in LA — simply don't apply to your state ADU.
That's not a loophole. It's written directly into the memo. And it changes how you should be thinking about SB 9 inventory in LA City.
The Problem With Regular ADU Lots in LA
In most of Los Angeles City's single-family zones, your FAR (floor area ratio) or RFA is the invisible ceiling on everything you build. On a typical R1 lot, you might have a house that already consumes the majority of your permitted floor area. When you go to add an ADU, the math gets brutal fast — the city will tell you that there's only 200 or 300 square feet of RFA remaining, capping your ADU at a size that barely qualifies as a studio.
State law stepped in and said cities can't use that trick to block ADUs entirely — they must allow at least an 800 sq ft detached state ADU regardless of FAR. But for many landlords, 800 square feet is the ceiling, not the floor. If you want a true income-generating unit — one that can rent for real money in LA — size matters.
This is where SB 9 + ZA Memo 143 changes everything.
What ZA Memo 143 Actually Says
[ZA Memo 143](https://planning.lacity.gov/odocument/184600d8-71d7-4d74-baf1-1f9cd2603320/ZA%20Memo%20No%20143-%20Implementation%20of%202019%20ADU%20Ord%20and%20State%20ADU%20Law%20(Updated%20based%20on%202022,%202023%20an.pdf) is the Los Angeles City Planning Department's official implementation memo for California ADU law. It's the document that tells plan checkers and zoning administrators exactly how to apply state ADU statutes to LA City properties.
One of its clearest provisions: RFA limits may not be enforced on state ADUs.
The memo is explicit. A state ADU — meaning an ADU built under California Government Code § 66323 rather than the local ordinance — is not subject to LA City's residential floor area calculation. The city cannot use its FAR math to shrink your state ADU below the minimums the state guarantees. And for attached state ADUs built within an existing or proposed dwelling, the memo shows no stated maximum size.
This has direct consequences for how you size and value an ADU on an SB 9 lot.
SB 9 Two-Unit Development: What You Actually Get
Senate Bill 9, in effect since January 2022, allows homeowners in single-family zones to build a second primary unit — effectively creating a duplex on what was formerly an R1 lot — without discretionary approval. In LA City, the SB 9 implementation memo clarifies exactly how these new units interact with the ADU rules.
On a lot using the SB 9 Two-Unit Development path (not an Urban Lot Split), here's what you can stack:
Two primary units (the SB 9 duplex itself)
Up to two detached state ADUs — each up to 800 sq ft, neither subject to RFA limits
One JADU — up to 500 sq ft carved from existing space
That's potentially five units on a single former single-family lot. And the two detached state ADUs sit entirely outside LA's RFA accounting.
For attached state ADUs proposed within the duplex structure itself, you have even more flexibility — state law sets no explicit maximum square footage, and ZA Memo 143 confirms the city's RFA can't block you. Your limits become practical building constraints — setbacks, height, lot coverage — not the abstract FAR math that kills regular ADU projects.
Why This Is a Bigger Deal in LA City Than Elsewhere
SB 9 is a statewide law, but not every city implements it the same way, and not every city has a ZA Memo 143. Most Orange County cities apply their own ADU ordinances, and while state law still protects minimum size guarantees, the explicit removal of FAR enforcement through a city-issued implementation memo is a Los Angeles City-specific advantage.
In cities like Anaheim or Costa Mesa, you're dealing with each city's own ADU ordinance, which may apply size limits in ways that are harder to navigate. In Long Beach, there's no equivalent administrative memo removing RFA enforcement at the city level. LA City's combination of a detailed planning memo that explicitly strips out RFA for state ADUs — stacked with SB 9's density allowances — creates a playbook that simply doesn't exist in most of the region.
If you're comparing an SB 9 lot in, say, Burbank to an SB 9 lot inside the City of Los Angeles proper, you're not comparing apples to apples. The LA City property is operating under a more investor-friendly interpretation of the law.
What This Means If You're Buying
If you're looking at SB 9-eligible properties in LA City, the analysis changes:
You're not just buying a duplex. You're buying a lot where the city has already published guidance removing RFA as a barrier to your ADU development. The planning infrastructure that stops most ADU projects — the FAR ceiling — has been explicitly addressed.
Your ADU underwriting should reflect real square footage potential, not worst-case RFA math. On a regular lot, an investor might pencil a 600 sq ft ADU because that's all the FAR allows. On an SB 9 lot in LA City, you should be starting from the state ADU minimum (800 sq ft detached) and working upward based on setbacks, lot coverage, and height — not RFA.
The unit count math is real. Five income units on a single-family lot — two SB 9 primary units, two detached state ADUs, one JADU — produces rental income that changes the cap rate story entirely compared to a standard ADU deal.
Before writing off an LA City SB 9 property because the RFA looks tight, verify the ADU potential during escrow — specifically confirming which ADU path (state vs. ordinance) applies to your project. That determination changes everything about the size you can legally build.
One Important Distinction: Urban Lot Splits Are Different
Not all SB 9 projects are the same. The Two-Unit Development path and the Urban Lot Split path operate under different rules, and this distinction matters.
Under the SB 9 implementation memo, lots that use both the Urban Lot Split and the Two-Unit Development path — either together or at different times — cannot add ADUs or JADUs. The unlimited-size advantage being discussed here applies to the Two-Unit Development path only.
If you're evaluating a property where a prior owner already recorded an Urban Lot Split, the ADU calculus changes significantly. Knowing how to search for ADU-potential homes in the first place — including understanding which SB 9 path a property has or hasn't used — is part of doing the deal right.
The Bottom Line
SB 9 lots in Los Angeles City aren't just about adding a second unit. When you layer in ZA Memo 143's explicit removal of RFA enforcement for state ADUs, you get a property type where the standard FAR ceiling — the wall that stops most ADU projects in their tracks — has been officially taken off the table.
The result is a lot where you can build more ADU square footage than the city's own zoning calculator would suggest, stack up to five units total, and operate from a legal framework that other Southern California cities haven't replicated.
That's not a common real estate play. It's a specific advantage baked into how LA City implemented state housing law, and if you're buying ADU investment properties in LA County, it's one worth understanding before you make an offer.
Questions about how this plays out on a specific property? Reach out — evaluating SB 9 potential alongside ADU path eligibility is exactly the kind of analysis that separates good ADU deals from great ones.
