New ADU Regulations for Multifamily Properties: What You Need to Know Unlocking New Housing Potential Through ADUs

           As California continues to battle a housing affordability crisis, recent changes to state legislation are creating new opportunities for property owners. In particular, multifamily property owners can now build more Accessory Dwelling Units (ADUs) than ever before, thanks to the 2025 updates to California ADU law. These changes are designed to support housing growth, streamline the permitting process, and eliminate long-standing barriers to adding livable units on existing properties.

Whether you’re a duplex owner or manage a 10-unit complex, the new laws offer significant incentives to expand your rental portfolio and contribute to statewide housing solutions.

Understanding the New ADU Regulations

Building on earlier reforms, California’s latest ADU laws make it easier to construct, legalize, and even sell ADUs on multifamily lots. Here are the key updates:

Key ADU Regulations for Multifamily Properties (Effective 2025)

Increased ADU Capacity (SB 1211):

Owners of multifamily buildings may now add up to eight detached ADUs per lot, depending on the existing number of units and compliance with local fire and safety codes. This is a major expansion from the previous cap of two.

Interior Conversion Flexibility:

Non-livable areas such as storage rooms, garages, and basements within multifamily structures may now be converted into ADUs. This allows property owners to create multiple new units without altering the building’s footprint.

Legalization of Unpermitted Units (AB 2533): 

If an ADU or Junior ADU (JADU) was built before January 1, 2020, without a permit, owners now have a legal pathway to bring these units into compliance, so long as they meet basic health and safety standards.

No Replacement Parking Required:

When converting existing parking structures into ADUs, local jurisdictions can no longer require replacement parking, eliminating a major cost and design challenge.

Pre-Approved ADU Plans (AB 434 & AB 1332):

Cities and counties are now required to offer pre-approved ADU building plans, helping streamline the design and permitting process for property owners.

Condo Conversion Option (AB 1033):

Where adopted by local municipalities, owners may now sell ADUs as condominiums, creating a new model for wealth-building and ownership in urban markets.

Faster Permit Review Process:

Permit applications for ADUs must now be reviewed within 60 days, with written feedback required if denied. This ensures a transparent, objective, and faster path to approval.

(For full details, visit the California Department of Housing and Community Development.)

How Alimo Architects Can Help

Understanding and acting on these new regulations can be complex, but that’s where we come in. At Alimo Architects, we help multifamily property owners transform underutilized spaces into compliant, high-performing rental units.

Our ADU Services for Multifamily Property Owners:

Feasibility & Compliance Reviews:

We assess your property’s eligibility for detached and internal ADUs under the new rules and determine the highest and best use of available space.

Custom ADU Design Solutions:

We integrate state-approved plans or create custom layouts to maximize unit count and ensure code compliance, all while preserving the character of your building.

Permit Management & Approvals:

Our team handles zoning checks, fire safety reviews, and comprehensive permit packages—saving you time and avoiding costly missteps.

Legalization of Existing Units:

We assist with documentation, inspection coordination, and upgrades to bring unpermitted units into legal standing.

Why Choose Alimo Architects?

Extensive Code Knowledge:

We stay ahead of evolving ADU laws and apply them with precision for each unique site.

Design That Adds Value:

Our architects craft practical and beautiful spaces that enhance your building’s livability and long-term investment potential.

Streamlined Execution:

From initial concept to final permit, we offer a one-stop shop to accelerate your project and reduce friction.

Ready to Maximize Your Multifamily Property?

The 2025 ADU laws create new pathways for growth, value creation, and community impact. Whether you’re looking to add new units, legalize existing ones, or prepare for future condo conversion opportunities, Alimo Architects is here to help.

📞 Contact us today to schedule your complimentary ADU consultation.

Let’s build the future of housing together.