SB 9: How to Unlock 4-Unit Development on Single-Family Lots in California

At Inform Construction Inc., we help clients turn this legislative opportunity into real-world value. Whether you're an investor, homeowner, or developer, our team can take your SB 9 project from concept to construction—efficiently and strategically.

SB 9 allows homeowners and property investors to either build a duplex on an existing single-family lot, or split the lot into two parcels and build up to two homes on each. This means you can now legally build up to four housing units on a lot that once allowed only one.

The law is designed to:

● Increase housing supply in established neighborhoods

● Promote homeownership and middle-income development

● Remove unnecessary barriers to small-scale, infill housing

Importantly, SB 9 requires ministerial (non-discretionary) approval, which streamlines the process and limits local opposition or delays.

To take advantage of SB 9, a property must meet the following criteria:

SB 9 provides two main development paths:

1. Duplex Development: Build a two-unit structure on a single-family lot without splitting it.

2. Lot Split + Duplex: Split the lot into two and build two units on each—totaling four units.

Depending on the zoning envelope and site layout, these projects can include:

● Detached or attached duplexes

● Modular or prefab unit configurations

● ADUs in combination with SB 9 duplexes (in some cases, per local ordinance)

Inform Construction Inc. delivers turnkey support for SB 9 projects across Los Angeles and surrounding markets.

1. Site Evaluation & Feasibility

● Confirm SB 9 eligibility and zoning

● Analyze site constraints, setbacks, and design options

● Develop pro forma for build-to-rent or build-to-sell scenarios

2. Planning & Entitlements

● Prepare architectural and civil plans

● Manage ministerial applications and lot split processes

● Coordinate with surveyors, utility providers, and local agencies

3. Construction & Delivery

● Execute ground-up construction with reliable cost control

● Manage inspections and delivery milestones

● Build efficiently using experienced subcontractors and suppliers

4. Sales & Leasing Support

● Prepare homes for sale or rental market

● Coordinate marketing, staging, and lease-up teams

● Advise on optimal exit strategies

SB 9 makes it possible to multiply the value of a single parcel, create income-producing housing, and contribute to solving California’s housing crisis—all while maintaining the scale and character of existing neighborhoods.

For investors, it’s a tool to generate long-term rental income. For homeowners, it offers the chance to expand family housing or fund retirement through downsizing. For developers, it opens the door to small-scale, high-yield projects with far less regulatory burden.

The potential for SB 9 development is already being realized across Los Angeles—and the window of opportunity is just beginning. If you’re evaluating your property or seeking new acquisition targets, Inform Construction Inc. can guide you through every step.

Contact us at informcm.com to schedule a feasibility assessment and learn how to make the most of SB 9.