How Big Can Your SB9 Unit Be in the City of Orange? It Depends on Your Lot Size.
If you're thinking about doing an SB9 lot split in the City of Orange, one of the first questions you're going to hit is: how big can I actually build?
The answer isn't a flat number. The City of Orange uses a tiered square footage table tied directly to your lot size — and it's written right into Ordinance No. 15-23, the city's local SB9 regulations. If you're planning a lot split, this is the number that determines how much living space you can put on each new parcel.
Here's what the ordinance actually says.
The Square Footage Table: What the City of Orange Allows Per Unit
Under Section G of Table 17.14.060, the City of Orange replaces the traditional Floor Area Ratio (FAR) requirement with a flat unit size cap based on lot area. That means instead of calculating a percentage of the lot, you're simply capped at a maximum square footage tied to how big the lot is:
Lot Area (Square Feet) Maximum
Unit Size1,200 – 4,999 800 sq ft
5,000 – 5,999 800 sq ft
6,000 – 6,999 800 sq ft
7,000 – 7,999 800 sq ft
8,000 – 9,999 850 sq ft
10,000 – 11,999 900 sq ft
12,000 – 14,999 950 sq ft
15,000 – 19,999 1,000 sq ft
20,000 – 39,999 1,100 sq ft
40,000 and greater 1,200 sq ft
This applies to each unit built on the new parcels created by the lot split — not the combined total. So if you're splitting a 10,000 sq ft lot into two parcels, each unit can be up to 900 sq ft.
What the Lot Split Rules Actually Require
The square footage cap is just one piece. Before you get to unit size, you need to clear the lot split requirements themselves.
Under the same ordinance, the two new parcels must be approximately equal in size, with one rule: neither parcel can be smaller than 40% of the original lot. So if you're splitting a 7,500 sq ft lot, neither resulting parcel can be smaller than 3,000 sq ft — and the minimum lot size allowed under SB9 in Orange is 1,200 sq ft.
Each new parcel can have up to two units on it (a primary dwelling plus an ADU, or two new units), which means a lot split could yield up to four units total on what was originally a single-family lot. If you want to see how investors have been running that math in LA County with a similar setup, this breakdown on SB9 triplex and fourplex strategies is worth reading.
Other development standards from the ordinance:
Height: 16 feet maximum, 1 story
Front setback: 20 feet
Side and rear setbacks: 4 feet
Existing structures: No setback required for an existing structure, or one rebuilt in the same footprint and dimensions
Why the Square Footage Cap Matters More Than You Think
Most investors focus on lot split eligibility first — whether the parcel qualifies, whether it's in a historic district, whether the existing structure counts. But the unit size cap is what actually determines the rent you can charge and the value you can build.
In most of the City of Orange's residential zones, standard lot sizes run between 6,000 and 10,000 sq ft. That puts most SB9 splits in the 800–850 sq ft per unit range. That's a functional 1-bedroom or a tight 2-bedroom — not a large unit, but rentable, especially in a supply-constrained market like Orange County.
The bigger lots (15,000 sq ft and up) open the door to 1,000–1,200 sq ft units, which can justify a 2-bedroom layout and a meaningfully higher rent. If you're evaluating a larger R1 parcel in the City of Orange for a potential split, those are the lots worth modeling first.
Before you go deep on any of this, it's worth doing the full pre-purchase eligibility check. I walk through exactly what to verify before you close escrow on an investment property so you're not finding these limits out after you're already in contract.
Existing Units Are Treated Differently
One thing the ordinance is clear about: if there's already a unit on the lot, it can maintain its existing FAR and lot coverage. But any expansion of that existing unit has to come into compliance with the current development standards in Table 17.14.070.
In practice, this means if you're working with a property that has an existing home you're keeping, the new units you add on the split parcels are subject to the square footage caps above — but the original home isn't forced to shrink or conform.
How This Affects Value When You Sell
The size limits under the City of Orange's SB9 rules have a direct impact on how a multi-unit SB9 property gets valued at appraisal. Smaller units — especially those under 850 sq ft — can be harder to comp in markets where ADU or second-unit comparable sales are limited. How a property with an ADU gets valued when you sell in Orange County explains exactly how appraisers approach this and where the methodology breaks down on smaller units.
If you're pricing an existing SB9 property to sell — or trying to figure out what a lot split project would be worth at completion — here's how Orange County sellers are pricing ADU homes right.
How to Finance an SB9 Lot Split in Orange
Once you know the unit sizes you're working with, the next question is how you're funding it. Construction loans, HELOCs, and DSCR products each work differently for SB9 splits, and the smaller unit sizes in Orange can affect your projected income — which in turn affects what a DSCR lender will qualify you for. This comparison of DSCR loans, HELOCs, and construction loans for multi-unit ADU projects walks through how each structure works and when to use which.
The Bottom Line
The City of Orange caps SB9 unit sizes based on lot area — not FAR — and most standard residential lots in the city will land you in the 800–850 sq ft range per unit. Larger lots open the door to more square footage, but even the ceiling (1,200 sq ft) is modest compared to what some other cities allow.
If you're evaluating a property in Orange for an SB9 lot split, the math starts with this table. Know your lot size, know your cap, then model your rents from there.
California HCD's resources on SB9 and the City of Orange Planning Division are the two official sources to cross-reference if you're doing your own due diligence on a specific parcel.
Questions about a specific property in the City of Orange? Reach out — I can help you run the numbers before you make any decisions.
