Everything You Need to Know About SB 9: How to Build More Than Just an ADU in California

California homeowners looking to maximize their property’s value have a powerful opportunity: Senate Bill 9 (SB 9). While most are familiar with ADUs (Accessory Dwelling Units), SB 9 opens the door to building full-size additional homes on a single-family lot—with or without a lot split.

If you’re planning to add space for family, generate rental income, or increase property value, this guide breaks down how SB 9 works, how it differs from ADU laws, and how to get started.

🔍 What Is SB 9?

SB 9, passed in 2021, is a California housing law that allows:

• Up to two full-size homes on a single-family zoned lot (no lot split required)

• The ability to split a lot into two parcels and build two homes per parcel (up to four homes total)

SB 9 was created to address the housing shortage by making it easier for property owners to create more housing, without requiring rezoning or discretionary approvals.

🏠 SB 9 Without a Lot Split

You don’t have to divide your property to take advantage of SB 9. Under the "two-unit development" option, you can:

• Keep your existing home and build a new full-size home in the backyard

• Replace your existing home with a duplex (two attached units)

This is ideal for:

• Multi-generational living

• Creating rental income

• Adding space without complex subdivision

Note: Under this path, the lot remains one legal parcel. You won’t be able to sell the new unit separately without a lot split.

🏛️ SB 9 With a Lot Split (Urban Lot Split)

The second option SB 9 offers is a lot split, where you:

• Divide one single-family lot into two legal parcels

• Build up to two units per new parcel

This allows you to:

• Develop up to four homes total (2 per parcel)

• Sell or transfer the new parcels independently

• Maximize investment returns or long-term equity

Lot split requirements:

• Each new parcel must be at least 1,200 sq. ft.

• The split must be roughly equal (40%/60% minimum balance)

• The original lot can’t have been split before under SB 9

🔀 Can You Combine SB 9 and ADUs?

In some cases, yes — SB 9 does not automatically disqualify a property from also including ADUs or JADUs, but the exact number of allowable units depends on the local jurisdiction’s interpretation and application of state law.

According to guidance from cities like Long Beach and others:

• On a standard single-family lot, you can generally have 2 primary units under SB 9 plus 1 ADU and 1 JADU

• On each parcel created through a lot split, local agencies may allow 1 ADU per lot in addition to the 2 units

However, some cities may limit total unit counts to 2 per parcel, regardless of configuration.

Check with your local planning department or consult a professional to understand your city’s specific policies.

Development Type	Max Units	Lot Split Allowed	ADUs Permitted?
ADU Path	1 home + 1 ADU + 1 JADU (3 total)	❌ No	✅ Yes
SB 9 (No Split)	2 homes + 1 ADU + 1 JADU (varies by city)	❌ No	✅ Yes (case-by-case)
SB 9 (With Split)	2 units per lot (4 total) + ADUs (case-by-case)	✅ Yes	✅ Possibly (varies by city)

✅ Eligibility Requirements for SB 9

To qualify for SB 9 development:

• Property must be in a single-family residential zone

• Located in an urbanized area or urban cluster

• Cannot be:

  • In a high-risk fire, flood, or historic area without mitigation

  • Under recent tenant protections (e.g., no Ellis Act evictions in past 15 years)

• You must maintain 4-foot setbacks from side and rear property lines

• You cannot demolish more than 25% of an existing structure’s walls (with exceptions)

Good news: SB 9 projects do not require CEQA environmental reviews and must be approved ministerially by your city—meaning no public hearings or subjective design reviews.

💼 Why SB 9 Is Better Than an ADU for Some Homeowners

SB 9 units:

• Can be larger than ADUs (subject to local height/FAR limits)

• Can be sold or financed separately (with lot split)

• Can be used for primary residence, family, or full-market rentals

ADUs:

• Are limited in size (typically 800–1,200 sq. ft)

• Must remain on the same parcel and cannot be sold separately

• Often come with owner-occupancy requirements for JADUs

If you have a large lot (5,000+ sq. ft) and want more flexibility, SB 9 may be the better path.

🔹 Step-by-Step: How to Get Started

1. Site Evaluation – We assess your lot for SB 9 and ADU feasibility

2. Design Consultation – Work with our architects to create efficient layouts

3. Construction Documents – We prepare architectural, structural, and Title 24 plans

4. Permit Submission – We handle city processing, plan check, and revisions

5. Build – Choose your contractor or let us recommend one from our trusted network

🚀 Ready to Build More Than an ADU?

Whether you're aiming to build two homes, split your lot into four units, or need guidance on combining SB 9 with ADU options, Only Think Green can help you every step of the way.

We specialize in:

• SB 9 design + permit sets

• Lot split analysis + strategy

• Local code compliance

• Serving Riverside, San Bernardino, Orange, and Los Angeles Counties

📲 Contact us for a free consultation:🔗 www.onlythinkgreen.com📧 design@onlythinkgreen.com🏠 Southern California Residential Architecture Experts