Everything homeowners ask about building an ADU in Santa Monica — answered with 2026 data.
Yes, ADUs are allowed in Any legal parcel zoned for single-unit or multiple-unit residential use (residential and mixed-use districts) with an existing or proposed primary dwelling (SMMC 9.31.025(E)); not allowed on a parcel with a Gov. Code 66499.41 multi-unit ownership project or where the unit would exceed the SB 9 duplex/lot-split cap in Santa Monica, CA. The maximum size for a detached ADU is 850 sq ft (studio/1-bedroom) or 1,200 sq ft (2+ bedrooms) under the local standards, 150 sq ft minimum; a garage with an internal connection to the ADU does not count toward the cap (SMMC 9.31.025(I)(1)(c)). The state-mandated alternative under 9.31.025(J) is 800 sq ft. Attached ADUs can be up to 850 sq ft. Santa Monica has an ADU-friendliness score of 8/10. Check our full Santa Monica ADU rules page for complete zoning details.
ADU construction in Santa Monica typically costs $250,000-$500,000. The cost per square foot averages $325-$550. Garage conversions are more affordable at $140,000-$245,000, while prefab ADUs cost $200,000-$350,000. Permit fees add Plan check and building permit fees are valuation-based under the City's adopted fee schedule (finance.smgov.net); Planning charges $985.11 for a deed-restriction application and $833.46 for a Coastal Zone Approval in Concept (fees effective July 1, 2026) to your budget. See our detailed Santa Monica ADU cost guide.
Detached ADUs in Santa Monica can be up to 850 sq ft. Attached ADUs are limited to 850 sq ft. Junior ADUs (JADUs) have a cap of 500 sq ft of floor area (150 sq ft minimum), within the walls of the existing or proposed single-unit dwelling including an attached garage, or in a new addition to the house; a recorded deed restriction is required (SMMC 9.31.025(I)(1)(b), (K)). Maximum height is Detached ADU: 2 stories or 24 ft (SMMC 9.31.025(I)(1)(c)), measured per SMMC 9.04.050 (usually from average natural grade; a land survey is required for 2-story or sloped-lot units). Attached ADUs and JADUs: the underlying district's height limit for the primary dwelling. Detached ADUs on multi-unit parcels: 24 ft. You are allowed up to Single-unit parcel: 1 converted ADU + 1 JADU + 1 detached ADU, plus 1 more attached or detached ADU in the R1 zone that must be deed-restricted as a rental or sold as a condo on a qualifying lot.
Rear setback: 4 ft (SMMC 9.31.025(I)); no setback for existing space or a structure rebuilt in the same location and to the same dimensions, including unpermitted structures built before Jan 1, 2020 that are converted to an ADU (Guide p.3). Side setback: 4 ft; a detached ADU must sit at least 4 ft from the primary dwelling, measured between exterior walls (SMMC 9.31.025(B), 'Detached'), and may share a wall with another detached ADU or accessory structure. Front setback: Not permitted within the required front setback of the underlying zoning district; a conversion of an existing structure already in the front setback may expand up to 150 sq ft for ingress and egress (SMMC 9.31.025(I)(1)(a)(ii)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None required for ADUs or JADUs, and parking removed to build one (garage, carport or driveway) need not be replaced (SMMC 9.31.025(L)); displaced parking may be relocated to the front half of the lot per SMMC 9.28.070(A)(1)(a)(ii). Coastal Zone parcels should confirm parking with the Coastal Commission. Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
ADUs: not required (SMMC 9.31.025; Guide pp.4, 9). JADUs: SMMC 9.31.025(K)(2) and the Nov 2025 Guide require the owner to live in the main house or the JADU; since Jan 1, 2026 state law (Gov. Code 66333(b), AB 1154) allows that only for JADUs that share a bathroom with the main house, so ask Planning how the city applies it. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Santa Monica is typically 60 days from a complete application, or the ADU is deemed approved (SMMC 9.31.025(G)); since Jan 1, 2026 the city must also issue a completeness notice within 15 business days (Gov. Code 66317, SB 543). A Coastal Zone CDP runs on its own 60-day clock (Gov. Code 66329). Plan check: Electronic Plan Review: a prescreen for completeness, then routed plan check with corrections issued by email; initial plan review fees are paid at submittal and final fees before issuance. Every ADU needs its own address via an Address Application. Pre-approved plans availability: Preapproved ADU Program under Gov. Code 65852.27 (AB 1332) accepts vendor-submitted Standard ADU Plans for detached ADUs only, with no modifications allowed; as of Sept 2026 the city lists no approved plans ('NONE AT THIS TIME').
Average ADU rental income in Santa Monica: 1-bedroom units rent for $3,000-$3,700/month, 2-bedroom units for $4,000-$4,700/month. Short-term rentals: No — ADUs and JADUs may not be rented for 30 days or less (SMMC 9.31.025(M)); the only carve-out is licensed home-sharing under SMMC Ch. Expected ROI: 5-8% annual return.
The minimum lot size for an ADU in Santa Monica is None — SMMC 9.31.025 sets no minimum lot size, and Gov. Code 66321 bars any lot-size minimum that would block an 800 sq ft ADU with 4 ft setbacks. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Santa Monica, a garage conversion typically costs $140,000-$245,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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