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Vol. I ·California ADU Desk ·Licensed · Bonded · Insured ·CSLB #1098432 ·BBB A+ Accredited ·120+ ADUs Delivered ·Starting $250K ·10–16% ROI ·Los Angeles ·Bay Area ·Vol. I ·California ADU Desk ·Licensed · Bonded · Insured ·CSLB #1098432 ·BBB A+ Accredited ·120+ ADUs Delivered ·Starting $250K ·10–16% ROI ·Los Angeles ·Bay Area ·
GoldenStateADU

Permitting · 8 min read · April 15, 2026 · 347 words

ADU vs SB9 lot split: which path actually fits your lot

Two state laws now let LA homeowners add density. SB9 splits the lot and creates a separately sellable parcel; ADU law adds a unit. The decision turns on three numbers — and one local opt-out.

Key takeaways

  • Lot size. SB9 requires the resulting parcels to be at least 1,200 sq ft each. Below 2,400 sq ft total, SB9 is off the table.
  • Slope. SB9 explicitly excludes lots with average slope greater than 25%. Most LA hillside lots fail this test.
  • Hazard overlays. Very High Fire Hazard Severity Zones, [Alquist-Priolo Earthquake Fault Zones](https://www.conservation.ca.gov/cgs/alquist-priolo), and floodways are SB9-ineligible by statute.

SB9 (the California HOME Act) and ADU law solve different problems. ADU law lets you add up to two units to an existing lot. SB9 lets you split a single-family lot into two parcels and build up to two units on each. They're stackable in theory, but LA has restrictive overlays that often force a choice.

The three numbers that decide

  1. Lot size. SB9 requires the resulting parcels to be at least 1,200 sq ft each. Below 2,400 sq ft total, SB9 is off the table.
  2. Slope. SB9 explicitly excludes lots with average slope greater than 25%. Most LA hillside lots fail this test.
  3. Hazard overlays. Very High Fire Hazard Severity Zones, Alquist-Priolo Earthquake Fault Zones, and floodways are SB9-ineligible by statute.

What SB9 actually unlocks

SB9 splits a lot 50/50 (or close to it), produces two separately sellable parcels, and allows up to two units on each parcel — for a theoretical maximum of four units. In practice, LA's enforcement of the owner-occupancy affidavit and the requirement that the splitter live on-site for three years dampens speculative use.

What ADU law unlocks

Stays as a single parcel. You can add one detached ADU plus one JADU (junior ADU) in many cases. No owner-occupancy requirement (suspended through 2025). Faster — by-right 60-day approval. Cheaper — no parcel split survey or new title insurance. The LADBS SB9 bulletin is the local interpretation.

Decision matrix

  • Want to sell off the new unit separately → SB9 (with all its caveats).
  • Want rental income, fastest path, lowest soft costs → ADU.
  • Lot under 2,400 sq ft, hillside, or in a hazard overlay → ADU.
  • Lot over 4,000 sq ft on a flat parcel outside hazard zones → SB9 worth modeling.

Sources

  1. SB9 Fact Sheet · California HCD
  2. California SB9 (2021) Bill Text · California Legislature
  3. Alquist-Priolo Earthquake Fault Zones · California Geological Survey
  4. LADBS Permits & Bulletins · LA Department of Building and Safety

FAQ · Permitting

Common questions on permitting

The questions readers send us most after this guide.

  1. What is SB-9 and does it apply to me?
    SB-9 (the California HOME Act) lets eligible single-family lots split into two parcels and/or add a duplex. We assess eligibility during the feasibility call — roughly 60% of LA single-family lots qualify on paper, fewer in practice once HPOZ, hillside, and coastal overlays are applied. SB-9 projects can stack with an ADU for up to four units on what was a single-family lot.
  2. What about hillside or coastal lots?
    Hillside requires a Methane District review (where applicable) plus a haul route plan if grading exceeds 1,000 cubic yards. Coastal Zone projects (anything west of Lincoln Blvd in Venice, for example) need a Coastal Development Permit on top of standard LADBS approval. Both are workable; both add 60–90 days.
  3. I'm in an HPOZ — can I still build?
    Yes, but with design review. Historic Preservation Overlay Zones require Certificate of Appropriateness from the cultural heritage commission before permits issue. We've shepherded projects through Miracle Mile, West Adams, Whitley Heights, and Spaulding Square HPOZs. Add 8–12 weeks for the COA process.
  4. Do you handle the permitting?
    Yes. We file with LADBS or your local building department, manage plan check, coordinate utility upgrades, schedule inspections, and deliver final sign-off. You don't visit the counter, we do.
  5. What setbacks and height limits apply?
    Statewide ADU law (AB 68/881) overrides most local restrictions: 4-foot side and rear setbacks, 16-foot height for detached one-story, 18-foot for two-story within ½ mile of transit. Front setbacks follow the underlying zone. We model your envelope at the schematic stage.

Sources & further reading

  • California Government Code §65852.2 — statewide ADU framework (ministerial review, 60-day clock).
  • LADBS — Accessory Dwelling Unit information bulletins and current permit fee schedule.
  • HCD — California Department of Housing & Community Development, ADU handbook (2024 update).
  • Internal data: 120++ ADU projects delivered across Los Angeles County, 2018–2025.

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