Quick answer: Adding an ADU to a duplex or multifamily property costs $60,000–$225,000 in Los Angeles, depending on the type of ADU and property conditions. APLA Construction (CA Lic #1136359) provides free estimates across Greater Los Angeles.
One of the most frequently asked questions APLA receives from Los Angeles property owners is: “Can I add an ADU to a duplex or apartment building?” The answer — as of 2026 — is a nuanced yes, thanks to California’s progressive ADU legislation. This guide explains the current rules for ADUs on multifamily properties in Los Angeles, the costs involved, and how SB 9 further expands your options.
California law now in Gov. Code § 66323(a)(3)–(4) (the rules formerly in Government Code § 65852.2, renumbered in 2025) allows ADUs on multifamily residential properties under specific rules:
On a multifamily property (duplex, triplex, apartment building), you may convert non-livable space (storage rooms, garages, common areas, carports, laundry rooms) into ADUs. You may convert as many as 25% of existing units or a minimum of 1 ADU — whichever is greater. These conversions do not require LADBS to impose parking replacement requirements.
On a lot with an existing multifamily building, you may add up to 8 detached ADUs, but no more than the number of existing units on the lot. On a lot with a proposed multifamily building, up to 2. These units can be held to the state height limits (16 feet, or 18 feet near major transit or on a lot with a multistory multifamily building) and 4-foot side and rear setbacks. Earlier versions of the law capped detached ADUs on multifamily lots at 2.
Senate Bill 9 (effective 2022) allows ministerial lot splits on single-family zoned lots — splitting one parcel into two, each of which can then have a primary dwelling and an ADU. This allows up to 4 units on what was previously a single-family lot. Not available on multi-family-zoned properties directly, but significant for SFR owners considering multifamily conversion.
| ADU Type on Multifamily | Typical Cost |
|---|---|
| Converting non-livable space (storage, garage) on duplex | $75,000–$140,000 |
| New detached ADU on multifamily lot (studio/1BR) | $145,000–$195,000 |
| New detached ADU on multifamily lot (2BR) | $175,000–$225,000 |
| Converting a carport or covered parking to ADU | $60,000–$110,000 |
Adding ADUs to a multifamily property stacks rental income and increases property value through both mechanisms:
On a duplex, state law allows up to 2 detached ADUs (no more than the number of existing units) plus at least 1 ADU converted from non-livable space such as storage or a garage (up to 25% of existing units, with a minimum of 1). On larger buildings the detached allowance rises with the unit count, up to 8 (Gov. Code § 66323(a)(3)–(4)).
No. California law specifically prohibits cities from requiring parking replacement for ADU conversions of existing non-livable space (garages, carports, storage) on multifamily properties. Los Angeles requires no parking for detached ADUs approved under these state multifamily rules (ZA Memo 143).
ADU rights are limited to residentially zoned parcels. Mixed-use commercial-residential properties may qualify if the residential component meets the minimum criteria. APLA evaluates each property for ADU eligibility during the initial consultation.
Yes. APLA (CA Lic #1136359) builds ADUs on single-family homes, duplexes, and multifamily properties throughout Los Angeles. Call (818) 818-4419 for a free ADU feasibility analysis of your specific property.
Call: (818) 818-4419
Email: info@aplaconstruction.com
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