How to LEGALLY Build 5 Units on a Single R1 Lot in Los Angeles
ADU
SB9
Multi-Unit Development
Introduction
A standard single-family lot in LA can legally hold five dwelling units. No rezoning, no variance, no discretionary approval. The pathway uses SB9 to create a duplex, California's State ADU law to add two detached units that don't count toward floor area limits, and a phased permitting approach to add a fifth attached unit after occupancy.
This article covers the full strategy, the legal basis, the phasing, the unit counts, the square footage rules, and the restrictions you need to know before you start.
ZA Memo 143: The Rulebook
The City of Los Angeles issued ZA Memorandum No. 143 on December 30, 2024. It's a joint document from the Office of Zoning Administration and the Department of Building and Safety that consolidates every ADU and JADU regulation currently in effect, incorporating State law changes through January 1, 2025, including SB 1211, AB 2553, SB 897, and AB 976.
It replaces all previous ADU memos (including ZA Memos 134 and 142). If you're permitting ADUs in LA, this is what your plan checker is referencing.
The reason it matters for this strategy: Memo 143 lays out clearly that State ADUs approved under Government Code § 66323(a) are exempt from local zoning and development standards. That includes Residential Floor Area (RFA) limits, lot coverage, overlay zone restrictions, and most local design standards. SB 1211 (2024) reinforced this by adding GC § 66323(b), which extended the exemption uniformly across all four State ADU types.
State ADUs vs. Ordinance ADUs
The memo distinguishes two ADU categories, and the difference drives the entire strategy.
Ordinance ADUs follow the City's local code (LAMC 12.22 A.33): subject to LA-specific height, setbacks, floor area limits, parking, and hillside restrictions.
State ADUs are approved under California Government Code § 66323(a) and are exempt from those local standards. RFA doesn't apply. Lot coverage doesn't apply. The City cannot use local zoning provisions to deny or shrink them.
Memo 143 gives a direct example: if an RFA limit or HPOZ standard would normally cap an ADU at 700 SF, that limit is overridden, the State guarantees up to 800 SF for a detached single-family State ADU. On a multifamily lot, the detached State ADUs have no square footage cap at all.
State ADU | Ordinance ADU | |
|---|---|---|
Subject to RFA | No | Yes |
Subject to Local Zoning | No | Yes |
VHFHSZ / Hillside Restrictions | No | Yes |
Setbacks | 4 FT Side & Rear | 4 FT Side & Rear |
Parking Required | No | Depends (Waivers available) |
Maximum Area | 800 SF for Single Family / None for Multi-Family | 1,200 SF |
Maximum Height | 16-20 FT | Zoning height limit |
Blueprint to a "Goldmine" in LA
The whole strategy rests on one move, turning a single-family property into a multifamily one. That single change flips which column of Memo 143 applies to your lot, and the multifamily column is where the real capacity lives.
Here's the sequence:
Create a duplex using SB9. Attach a second unit to the existing home, or demolish and build new. The lot now has a proposed multifamily dwelling.
File two detached State ADUs at the same time. GC § 66323(a)(4) allows up to two detached ADUs on a lot with a proposed multifamily dwelling. These are State ADUs, exempt from RFA, no square footage cap, no local zoning restrictions.
Get the Certificate of Occupancy for the duplex. The property status shifts from "proposed" to "existing" multifamily.
File for one attached ADU. Now available because the duplex is an existing multifamily dwelling. That's unit five.
Two phases. Five units. The duplex and its floor area live within RFA. The two detached State ADUs don't. The fifth unit comes online after occupancy.
Phase 1: SB9 Duplex + Two Detached State ADUs
Start with an existing single-family dwelling on an R1 lot. Under SB9, you convert or rebuild it as a two-unit development — either by attaching a second unit to the existing home, or by demolishing and building a new duplex.
The duplex qualifies as a proposed multifamily dwelling. That shifts the property from the single-family ADU column into the multifamily ADU column of Memo 143's Table 1, and that's where the detached State ADU allowance lives.
Memo 143, page 4, states that an applicant may propose an SB9 duplex in conjunction with up to two detached State ADUs under GC § 66323(a)(4)(A)(iii). "In conjunction" means the building permit applications are submitted at the same time or while one is still open.
These two detached ADUs are State ADUs. They do not count toward RFA. They have no State-imposed square footage cap. The only constraints are the building envelope, 4-foot side and rear setbacks, and the height limit.
After Phase 1, you have four units on the lot:
Unit | Type | RFA Exempt? |
|---|---|---|
1 | Primary dwelling (existing or new) | No |
2 | SB9 attached unit (duplex) | No |
3 | Detached State ADU | Yes |
4 | Detached State ADU | Yes |
The duplex maxes out the lot's buildable RFA. The two State ADUs sit outside that calculation entirely.
Phase 2: The Fifth Unit (After Certificate of Occupancy)
Once the duplex receives its Certificate of Occupancy, it transitions from a "proposed" multifamily dwelling to an "existing" one. That status change unlocks an additional ADU option.
Memo 143 states directly: "Once a Certificate of Occupancy for the duplex has been obtained, an attached ADU may be permitted on the Lot."
You have two paths for this fifth unit:
Path A
Ordinance ADU (LAMC 12.22 A.33): One attached ADU per lot. Subject to local development standards. The size limit is 50% of the existing dwelling's floor area, but the code guarantees a minimum of 850 SF, or 1,000 SF if the ADU has more than one bedroom. RFA cannot reduce it below those thresholds.
Path B
State ADU under GC § 66323(a)(3): Allows conversion of existing non-livable space within the multifamily structure, storage rooms, garages, basements, attics, into ADU units. Up to 25% of existing dwelling units, minimum one. For a duplex (2 units), 25% rounds to 1 unit minimum. No square footage cap, but you're limited to whatever non-livable space already exists inside the building.
Either path gets you one attached ADU. That's unit number five.
Realistic Numbers on a Typical LA Lot
A standard R1 lot in Los Angeles runs 5,000 to 7,500 SF. The existing home is usually 1,200 to 1,500 SF.
Unit | Type | Approx. Size | Counts Toward RFA? |
|---|---|---|---|
1 | Primary dwelling | 1,200–1,500 SF | Yes |
2 | SB9 attached unit | 800–1,200 SF | Yes |
3 | Detached State ADU | Up to building envelope | No |
4 | Detached State ADU | Up to building envelope | No |
5 | Attached ADU (Phase 2) | 850–1,000 SF | Depends on path |
The detached State ADUs have no square footage cap. The real limit is what fits within 4-foot side/rear setbacks and the height cap. On a 50×100 ft lot, after accounting for the duplex footprint, each detached ADU could realistically be 600 to 800+ SF.
Total potential across all five units: roughly 4,500 to 5,500+ SF of livable space, on a lot where the RFA might normally cap total floor area well below that.
Height Limits for Detached State ADUs
Height is measured per the LAMC, based on the applicable zone, Height District, or overlay. For detached State ADUs under GC § 66323(a)(4), the limits break down as follows:
Limit | Bonus |
|---|---|
16 FT | Base Height |
Additional 2 FT | if the main structure is multistory, or within ½ mile walking distance of a major transit stop or high-quality transit corridor |
Additional 2 FT | if the ADU roof pitch matches the primary dwelling's roof pitch |
A flat roof of 2% slope or less is not considered a roof pitch. If the primary dwelling has multiple pitches, the ADU only needs to match one of them.
Restrictions Worth Knowing
No JADU. Once you use the multifamily ADU column, single-family ADU options are off the table for that lot. Memo 143 (page 3): "either the single-family ADU options or the multifamily dwelling ADU options can be used on the Lot, but not both combined on the same Lot." That means no Junior ADU in this scenario.
Parking. The two detached State ADUs require no parking, full exemption under GC § 66323. SB9 duplex units typically require none either. The attached ADU may or may not require parking depending on transit proximity, historic district location, or whether it's filed concurrently with a new dwelling.
Replacement parking. Demolishing a garage to build the ADUs does not trigger replacement parking when the demolition is in conjunction with ADU construction. Confirmed in Memo 143, Q.28.
Fire sprinklers. Cannot be required for ADUs if they weren't required for the existing primary residence, even in Very High Fire Hazard Severity Zones (GC § 66314(d)(12)).
Non-conforming conditions. Existing zoning non-conformities on the property don't need to be corrected to permit the ADUs. The City also can't require correction of non-conformities created by adding the ADU (Memo 143, Q.25 and Q.26).
Ministerial process. ADU permits are ministerial, no public hearing, no discretionary review, no CEQA. If the plans comply, the City must approve within 60 days.
Summary
Phase | Action | Units | Running Total |
|---|---|---|---|
Existing | Single-family dwelling | 1 | 1 |
Phase 1 | SB9 attached unit (duplex) | +1 | 2 |
Phase 1 | Detached State ADU #1 | +1 | 3 |
Phase 1 | Detached State ADU #2 | +1 | 4 |
Phase 2 (after C of O) | Attached ADU | +1 | 5 |
The two detached State ADUs are the core of this strategy. They carry no square footage cap, no RFA impact, and no local zoning restrictions. The duplex and its RFA can be maximized independently. The fifth unit is unlocked by the transition from "proposed" to "existing" multifamily status after the Certificate of Occupancy.
References:
ZA Memorandum No. 143, City of Los Angeles (December 30, 2024)
California Government Code §§ 66310–66342
GC § 66323(a) and (b) — State ADU provisions
Senate Bill 9 (2021) — Two-Unit Development
SB 1211 (2024) — State ADU exemption clarification
HCD ADU Handbook (January 2025)
LAMC Section 12.22 A.33
EHDM Group Inc. is a licensed California General Building Contractor. We handle residential design, permitting, and construction across Los Angeles — including multi-unit ADU developments like the one described here.
