SB9 Promised San Diego Homeowners a Lot Split Boom. Three Years In, Only 11 Have Finished (2026)
When California passed SB9 in 2021, the pitch was simple and dramatic: any owner of a single-family lot could split it in two and add a second home on each half, turning one house into as many as four. Critics called it the end of single-family zoning as California knew it. Supporters called it one of the most important housing bills in a generation. Four years into the law actually being on the books, San Diego's real numbers tell a much quieter story, and there's a genuine legal fight still playing out over whether the law even applies here the way everyone assumed it did.
What SB9 actually lets you do
SB9, officially the California HOME Act, gives an owner of a qualifying single-family lot two separate options, and it's worth knowing both since they get mixed up constantly. The first is an urban lot split, dividing one parcel into two separate, roughly equal lots that can then be sold or developed independently, each new lot capable of holding its own home. The second is a two-unit development, converting an existing single-family home into a duplex, or adding a second unit to the lot, without touching the parcel lines at all. Combine both options on a single original lot and you can theoretically end up with four total units where there used to be one. In San Diego specifically, a lot has to be at least 2,400 square feet to qualify for a split, and the resulting two parcels generally have to divide close to 50/50, or as uneven as 60/40 depending on the specifics. The approval process is ministerial, meaning the city has to approve a qualifying application without a discretionary hearing and without the kind of full CEQA environmental review that slows down a lot of other development in California.
The catch that keeps this from being a free-for-all
SB9 comes with real strings attached, and they're a big part of why it hasn't produced the flood of projects a lot of people expected. If you do an urban lot split, you're required to live in one of the resulting units as your primary residence for at least three years after the split, which immediately rules out the purely speculative flip-and-sell version of this that a lot of early coverage implied. Short-term rentals are off the table entirely on SB9 units, with any rental or lease required to run at least 31 days. And while the approval process skips a discretionary public hearing, you still have to meet objective zoning standards around things like setbacks, parking, and lot configuration, which isn't a rubber stamp so much as a faster, more predictable version of the normal process.
The numbers that show how slowly this has actually moved
Here's the gap between the law's reputation and its real footprint. Between March 2022, shortly after SB9 took effect, and June 2026, the City of San Diego received a total of 66 SB9 applications, 51 for urban lot splits and 15 for two-unit developments without a split. Of those, only 14 had been permitted, and just 11 had actually been completed. That's genuinely a small number for a major metro area more than four years into a law that was supposed to meaningfully add to housing supply one lot at a time. It's worth comparing that pace to the ADU boom covered elsewhere on this blog, where San Diego has seen thousands of permits over a similar stretch. SB9 simply hasn't produced anything close to that volume, and the owner-occupancy requirement, the cost and complexity of actually subdividing a parcel, and the practical difficulty of financing and building a second freestanding home on a newly created small lot are all real explanations for why.
The legal fight that's been hanging over the whole law
Separate from the adoption numbers, SB9 has spent real time in court, and the outcome has directly touched San Diego's own backyard. Del Mar, along with Redondo Beach, Carson, Torrance, and Whittier, sued the state back in 2022, arguing that as charter cities, a specific legal category that includes both Del Mar and San Diego itself, they have constitutional home-rule authority over their own municipal affairs that SB9's mandate improperly overrides. A Los Angeles County Superior Court judge agreed in April 2024, ruling that SB9 was unconstitutional as applied to charter cities, since the law's stated purpose of expanding affordable housing wasn't closely enough tied to what the mandate actually required. That ruling, if it had stuck, would have meant SB9 simply didn't apply in places like Del Mar or San Diego at all.
It didn't stick. A Court of Appeal reversed that decision on November 12, 2025, putting SB9 back in force statewide, charter cities included, while sending the underlying constitutional question back down to the trial court for reconsideration under SB 450, a newer law that took effect January 1, 2025, specifically written to reinforce SB9's reach into charter cities and add a firm 60-day decision deadline for cities reviewing applications. As of right now, SB9 is active, enforceable law in San Diego. But the constitutional fight isn't fully resolved, it's just back at square one at the trial court level, which means this is worth watching rather than treating as permanently settled.
Why this matters even with such a small number of completed projects
Eleven completed projects citywide might make SB9 look almost irrelevant, but that undersells what it's actually doing for individual property owners who do use it. A homeowner sitting on a larger-than-average single-family lot, particularly in an older, less densely built neighborhood, has a real, legally protected path to add meaningful value, either by creating a second buildable lot to sell, by adding a unit for a family member or rental income, or by eventually subdividing an inherited property among multiple owners. The fact that relatively few people have used this option so far doesn't mean it's not useful, it means a lot of eligible homeowners either don't know it exists, don't have a lot that pencils out once actual construction costs are considered, or aren't ready to commit to the three-year owner-occupancy requirement that comes with a full lot split.
How this compares to the ADU path
For a lot of San Diego homeowners, the more useful comparison isn't whether SB9 is popular, it's whether SB9 or a standard ADU, covered in detail in this blog's ADU guide, better fits their specific property and goals. An ADU doesn't require splitting your parcel or living in either resulting unit, and the permitting process has had years longer to mature, which is a big part of why ADU volume dwarfs SB9 volume. SB9 makes more sense specifically when a homeowner wants to create a genuinely separate, sellable parcel rather than just adding a rental unit on their existing lot, a meaningfully different goal that happens to come with meaningfully more process and commitment attached.
What this means if you're a homeowner considering SB9 in San Diego
Confirm your lot actually meets the 2,400-square-foot minimum and can be divided into two roughly balanced parcels under the city's current standards before assuming a split is viable, and go in understanding the three-year owner-occupancy requirement as a real commitment, not a formality. Run the actual construction and subdivision costs against what a new buildable lot would realistically sell for or rent for in your specific neighborhood, since the math varies enormously depending on lot size, location, and local construction costs, and a project that looks great on paper citywide can still not pencil out on your specific block.
What this means if you're buying a property that's already been through an SB9 split
Verify the owner-occupancy history and current compliance status directly rather than assuming a previously split lot is automatically clean and fully resolved, since the three-year residency requirement runs from the split itself and ongoing compliance can matter to a future sale. It's also worth asking directly whether the specific jurisdiction's SB9 application was processed before or after the November 2025 appellate ruling, since anything processed during the period when the charter city exemption was in effect could carry its own wrinkle worth a closer look with a real estate attorney.
The bottom line
SB9 is real, active law in San Diego right now, reinforced rather than undercut by the most recent court ruling, but its actual footprint on the ground has been tiny, just 11 completed projects since 2022 against a much larger wave of ADU construction over the same period. The ongoing legal fight, with Del Mar as one of the lead plaintiffs, means the law's long-term status at charter cities isn't fully settled even though it's enforceable today. For the right lot and the right owner, SB9 remains a genuine, legally protected path to real added value, it's just a narrower, more demanding path than the original headlines suggested. If you want help figuring out whether your own property is a realistic candidate for an SB9 split or a standard ADU instead, reach out and we'll go through the real numbers together.
