Most owners assume adding units to an existing apartment building means a major project — entitlements, neighbors, years. For a redevelopment, that is right.
For adding two or three units to a building you already own, state ADU law has quietly become generous, and most owners have not caught up to where it landed.
Two allowances, and they stack
California Government Code section 66323 gives owners of existing multifamily property two separate rights. They are independent, which means you can use both on the same property.
Conversion of non-livable space. You may convert portions of an existing multifamily structure that are not currently livable space — storage rooms, boiler rooms, garages, attics, basements, hallways — into ADUs, up to 25% of the existing unit count, minimum one. A twelve-unit building can add three this way.
Detached units. Here is the change most owners have missed. SB 1211, effective January 1, 2025, raised the detached ADU limit from two to up to eight, not to exceed the number of existing units. A six-unit building can add up to six detached. A twelve-unit building can add up to eight.
Stack them and a twelve-unit building has a theoretical path to twenty-three units. Theoretical, because lot area, setbacks, utilities, and access will bind long before the statute does. But the legal ceiling is no longer the constraint it was three years ago.
SB 1211 also prohibits the city from requiring replacement parking when an uncovered space is demolished to build an ADU. That removes what used to be the most common project-killer on tight LA lots.
The rent control question decides everything
This is the part that determines whether the project works, and it is not intuitive.
For a pre-October-1978 property in the City of Los Angeles:
- A new detached ADU is generally not subject to the Rent Stabilization Ordinance. The original building stays covered; the new unit is not. You set market rent and it stays at market.
- A new attached ADU is likewise not RSO-covered — unless there was an Ellis Act withdrawal in the prior five years — but it does fall under the Just Cause Ordinance, which governs evictions rather than rent.
- Converting existing non-habitable space produces a unit that is JCO-covered but not RSO-regulated. Storage room, garage, boiler room. This is the good outcome.
- Converting existing habitable space can pull both the new unit and the original unit into RSO regulation. This is the bad outcome, and it is the trap.
So the sequence matters enormously. Carving a new studio out of an oversized existing apartment may look like the cheapest construction on the property and turn out to be the most expensive decision, because it can convert a market-rate unit into a stabilized one permanently.
The parking obligation the state did not erase
One more distinction owners routinely collapse.
SB 1211 stops the City from requiring you to replace demolished parking. It does not relieve you of your obligation to the tenant.
Under the RSO, where a housing service provided at the start of a tenancy is taken away, the owner must reduce that tenant's rent by the reasonable replacement cost of the service. If your tenants have had parking spaces since they moved in and you build over them, you owe rent reductions — regardless of what the city does or does not require.
On a building where eight tenants have parking and street parking runs $150 a month, that is $14,400 a year of permanent income reduction. At a 5.5% cap, roughly $262,000 of value. That number belongs in the project pro forma alongside construction cost, and it usually is not there.
Unpermitted units you already have
If your building has units that were built without permits, state law has moved in your favor.
AB 2533, effective 2025, extended amnesty to unpermitted ADUs and junior ADUs built before January 1, 2020 — previously the cutoff was 2018. Cities cannot charge impact fees on units legalized this way, must publicize the amnesty, and may inspect and recommend corrections without penalizing the applicant. They retain the right to deny if the unit is genuinely substandard under the Health and Safety Code.
There is a live dispute here worth knowing about. In August 2025, California's Department of Housing and Community Development rejected the City of Los Angeles's position that the 25% conversion cap also limits units legalized under the amnesty statute. HCD held the two provisions operate independently and that LA cannot use one to cap the other. We have not been able to confirm how the City ultimately responded, so treat this as unsettled — but if you have been told your unpermitted units cannot be legalized because of the 25% cap, that answer may be wrong.
Legalizing a unit converts income an appraiser will not count and a lender will not underwrite into income that both will. That is often worth more than the permit costs.
What changed in the last year
Four ADU bills were signed in fall 2025:
- SB 543 (effective January 1, 2026) confirms converted and detached ADUs may be combined on multifamily lots, defines ADU size as net interior livable space, exempts units of 500 square feet or less from school fees, and requires the city to review an application for completeness within 15 business days.
- SB 9 of the 2025 session — not the 2021 lot-split law — voids local ADU ordinances that are not submitted to HCD within 60 days of adoption, with state standards applying by default.
- AB 1154 eliminates the owner-occupancy requirement for junior ADUs that have their own bathroom.
- AB 462 sets 60-day decisions on coastal development permits for ADUs.
Two things people ask about that do not apply:
- SB 9 lot splits (the 2021 law) do not apply to multifamily-zoned property. LA City Planning is explicit: it applies only in single-family zones.
- AB 1033, which allows ADUs to be sold separately as condos, requires the city to opt in by ordinance. The City of Los Angeles has not. San José, Santa Monica, and unincorporated San Diego County have. Confirm current status before relying on this either way.
What about the density bonus programs?
Owners hear about Transit Oriented Communities and the newer Citywide Housing Incentive Program and wonder if they apply.
For an owner keeping the building and adding a few units, generally no. TOC and CHIP are redevelopment tools — they reward demolishing and building substantially bigger, with affordability requirements attached. Critically, they trigger one-for-one replacement of any RSO units lost, plus relocation obligations and potential Ellis Act exposure.
If your plan is to keep the building, ADUs under section 66323 are the practical path. If your plan is to tear it down, that is a different analysis and a much bigger one.
We would also note that the relationship between TOC and the newer CHIP program is not clearly documented on the City's own pages, and we would not rely on either without a conversation with Planning first.
How we look at these
A realistic ADU analysis on an apartment property has five inputs: where the non-habitable space actually is, what the construction costs, what the new units rent for at market, what rent reductions you owe existing tenants for services lost, and whether the added income supports the debt to build it.
The fifth one is where most of these projects live or die. Adding $60,000 of annual market-rate income to a building is worth roughly $1.1 million at a 5.5% cap and supports around $640,000 of additional loan. If the project costs $450,000, that works. If it costs $900,000, it does not, no matter how much the statute allows.
ADU law has changed substantially three years running. Confirm current requirements with LA City Planning and LADBS before designing anything.
Sources
- California Government Code section 66323, ADUs on multifamily property (see HCD and legislative summaries)
- California HCD, technical assistance letter to the City of Los Angeles, August 14, 2025
- LA Housing Department, ADUs and the RSO
- LA City Planning, SB 9 FAQ
- LA City Planning, Citywide Housing Incentive Program