Buena Park SB-9: The Unit Size Rules That Most Property Owners Get Wrong
If you own a single-family home in Buena Park and you're thinking about using SB-9 to add a second unit or split your lot, the first question you need to answer isn't "can I do it?" — it's "how big can I actually build?"
Buena Park's SB-9 urgency ordinance has strict unit size limits, and they're more restrictive than most property owners expect. Get this wrong upfront and you're either over-building (which gets flagged at plan check) or under-building (leaving rentable square footage on the table). Here's exactly what the ordinance says.
What SB-9 Actually Allows in Buena Park
Under California's SB-9 law (Government Code § 65852.21), cities must allow up to two primary dwelling units on a single-family lot in most residential zones. Buena Park adopted its implementing ordinance effective January 1, 2022.
There are two separate SB-9 pathways: a two-unit project (adding a second primary dwelling to an existing lot) and an urban lot split (dividing the lot into two parcels). The unit size rules apply to both, but they work differently — and confusing them is the most common mistake I see.
The Unit Size Cap: 500 to 800 Square Feet
This is the number that matters most.
Under Buena Park's ordinance, every new primary dwelling unit built through an SB-9 two-unit project must be between 500 and 800 square feet. Not 850. Not 499. The ordinance is explicit: total floor area must be "less than or equal to 800 and more than 500 square feet."
That's a tight band. For context, 800 square feet is roughly the size of a well-configured two-bedroom apartment — workable for a rental unit, but not a sprawling second home.
What About Your Existing House?
The size cap applies only to the new unit added through SB-9. Your existing home is treated differently depending on its current size:
If your existing home is larger than 800 sq ft: It stays as-is. You cannot expand it as part of the two-unit project — the ordinance freezes it at its current lawful floor area.
If your existing home is smaller than 800 sq ft: You can expand it up to 800 sq ft as part of the project, or afterward.
This matters for income planning. If you own a 1,400 sq ft home and you're adding an 800 sq ft SB-9 unit behind it, you're working with roughly 2,200 sq ft of total residential space on one lot. The income potential stacks up, but the SB-9 unit itself is the ceiling — you can't negotiate the city up to 900 sq ft. The ordinance doesn't leave room for discretion.
Urban Lot Splits: The Lot Size Minimums
If you're pursuing an urban lot split instead of (or in addition to) a two-unit project, the relevant size rules shift from units to land.
Buena Park requires:
The original lot must be at least 2,400 square feet to qualify for a split
Each resulting lot must be at least 1,200 square feet
Each resulting lot must be between 40% and 60% of the original lot area — so you can't split unevenly
That 40/60 rule is the one that catches people off-guard. If your lot is 6,000 sq ft, you can end up with a 2,400 sq ft lot and a 3,600 sq ft lot. That's legal. But you can't create a 1,200 sq ft sliver and keep a 4,800 sq ft remainder — the split has to land within that 40/60 band.
On a lot created through an urban lot split, no more than two dwelling units of any kind are allowed — that includes primary units, ADUs, and JADUs. The ordinance is clear that "unit" means any dwelling unit. So if you split and build two primary units, you're at your maximum. There's no room to add an ADU on top.
On a non-split lot, the math is different: you can have a two-unit SB-9 project plus any ADU or JADU that state law requires Buena Park to allow under its ADU ordinance. That's potentially three or four units on one lot, depending on the configuration. Investors are actively engineering these multi-unit setups in LA County with SB-9 and ADUs — the same logic applies in Buena Park.
Height and Lot Coverage: The Other Limits That Constrain Size
The 800 sq ft cap isn't the only constraint on how much you can build. Two additional rules shape the physical footprint:
Height:
On lots larger than 2,000 sq ft: new SB-9 primary units are capped at one story or 16 feet
On lots smaller than 2,000 sq ft: new units can go up to two stories or 22 feet, but any portion above one story must step back five additional feet from the ground floor — and no balcony or second-story projection can intrude on that step-back
Lot Coverage:
Maximum building coverage is 40% of net lot area across all single-family zones
The ordinance carves out one protection: the 40% cap won't be enforced if it would prevent you from fitting two primary units at 800 sq ft each
In practice, the height cap is what usually bites on smaller lots. A single-story 800 sq ft footprint is a viable build. But if your lot is compact and you were hoping to stack square footage vertically, the 16-foot limit on larger lots shuts that down.
The Four-Foot Setback Rule
New SB-9 units must maintain a four-foot interior side yard and rear yard setback from the property line. On corner lots, a 10-foot setback from the side yard abutting a street is required.
These setbacks exist alongside whatever setbacks the underlying zone imposes — so if your RS-8 zone has larger rear yard requirements, those apply unless the four-foot SB-9 setback gives you more flexibility. Existing structures that are legally established are exempt: you don't need to bring a legal nonconforming garage into compliance just because you're adding an SB-9 unit nearby.
One Parking Space Per Unit (With a Transit Exception)
Each new primary dwelling must have at least one off-street parking space. The exception: if the dwelling is located within half a mile of a high-quality transit corridor, a major transit stop, or a car-share vehicle location as defined under the Public Resources Code, the parking requirement is waived.
Buena Park is served by several OCTA bus routes. Whether any of those corridors qualify as "high-quality transit" under the specific statutory definition is a site-specific question — check with the city before assuming the waiver applies.
What You Can't Do Under Buena Park's SB-9 Ordinance
A few hard stops worth knowing before you plan:
No short-term rentals. Buena Park requires a deed restriction that expressly prohibits any rental for less than 30 days. If you're thinking about Airbnb income to make the numbers work, it won't work here — the restriction runs with the land.
No condos or separate conveyance. Primary dwelling units on the same lot cannot be sold separately. No condominium airspace divisions, no common interest developments. If you're hoping to build-and-sell individual units, SB-9 in Buena Park doesn't support that exit.
Owner occupancy required (on non-split lots). If the lot is not created by an urban lot split, the deed restriction requires the individual property owner to occupy one of the dwellings as their primary residence.
No LLCs or corporations. Only natural persons (or qualifying community land trusts and nonprofits) can apply. An LLC-owned property is not eligible.
Buena Park vs. Comparable Markets
Buena Park is one of those North OC cities where ADU and SB-9 comp data is thin compared to markets like Garden Grove or Anaheim — which means there's less price discovery on what an 800 sq ft SB-9 unit actually adds to a sale or appraisal. That's not a dealbreaker, but it's something to understand when you're projecting value.
The 800 sq ft cap also means the income upside per unit is more limited than what you'd get from a full-size permitted ADU. The 3 SoCal property benefits that stack into $68,000/year show the math on income stacking — but SB-9 units in a city with strict size limits are going to come in at the lower end of that range unless the lot configuration allows for ADU stacking on top.
Before you commit to the SB-9 path in Buena Park, it's worth verifying the property is ADU-eligible and understanding how the unit will be treated at appraisal — because how a home with an additional unit gets valued when you sell depends heavily on comparable income data that's still sparse in this market.
The Practical Takeaway
If you're planning an SB-9 project in Buena Park, here's what to anchor on:
The new unit is capped at 800 sq ft and floored at 500 sq ft. On most lots, it'll be one story and 16 feet tall. You get a four-foot setback from the rear and interior side property lines. You need one parking space unless you're near qualifying transit. And a deed restriction will prohibit short-term rentals and require owner occupancy on non-split lots.
California HCD's ADU Handbook is worth reading alongside the local ordinance — state law sets the floor, and Buena Park's rules layer on top. Where state and local rules conflict, state law generally prevails, but the city's specific standards (like the 500–800 sq ft band) apply to the extent they're within the state-authorized range.
If you own a single-family lot in Buena Park and want to understand what's actually buildable on your specific parcel, I'm happy to walk through it. The lot size, current home footprint, zone designation, and proximity to transit are the four variables that determine what SB-9 actually allows you to do here.
Dylan Serna is an ADU specialist real estate agent serving buyers and sellers across Orange County and LA County. Questions about SB-9 eligibility or ADU value in Buena Park? Reach out directly.
