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 (including residential and mixed-use properties) with an existing or proposed dwelling (SMMC 9.31.025) 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). Attached ADUs can be up to 850 sq ft (studio/1-BR) or 1,200 sq ft (2+ BR), but not more than 50% of the existing primary dwelling (minimum 800 sq ft guaranteed for conversions of the primary dwelling). 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 $350-$550. Garage conversions are more affordable at $140,000-$245,000, while prefab ADUs cost $200,000-$350,000. Permit fees add Valuation-based plan check and building permit fees paid through Citizen Access; confirm current totals with Santa Monica Building & Safety via the 311 system to your budget. See our detailed Santa Monica ADU cost guide.
Detached ADUs in Santa Monica can be up to 850 sq ft (studio/1-bedroom) or 1,200 sq ft (2+ bedrooms). Attached ADUs are limited to 850 sq ft (studio/1-BR) or 1,200 sq ft (2+ BR), but not more than 50% of the existing primary dwelling (minimum 800 sq ft guaranteed for conversions of the primary dwelling). Junior ADUs (JADUs) have a cap of 500 sq ft (within the footprint of an existing or proposed single-unit dwelling). Maximum height is Detached: 2 stories or 24 ft (measured per SMMC 9.04.050, typically from Average Natural Grade); attached ADUs and JADUs: underlying zoning district height limits for the primary dwelling. You are allowed up to Single-unit-dwelling parcels may combine: 1 converted ADU + 1 JADU + 1 detached ADU, plus 1 additional attached ADU on R1-zoned parcels — up to 3 accessory units alongside the main home on a qualifying lot.
Rear setback: 4 ft; none for conversions of existing structures (including pre-Jan 1, 2020 unpermitted structures being legalized). Side setback: 4 ft; minimum 4 ft separation between a detached ADU and the primary dwelling, measured between exterior walls. Front setback: Not permitted within the required front setback of the underlying zone (JADUs within existing structures are exempt). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
No on-site parking required; parking eliminated by a garage conversion does not need to be replaced (contact Rent Control re: rent-controlled parking amenities; Coastal Zone parcels should confirm 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.
Not required for ADUs. City guide requires owner-occupancy for JADUs (SUD or JADU); AB 1154 (eff. Jan 1, 2026) removes this for JADUs with separate sanitation — state law prevails. 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 — application deemed approved if the city does not act within 60 days (SMMC per SB 543, eff. Jan 1, 2026); Coastal Zone CDP adds months to the front end. The plan check process takes approximately Electronic Plan Review with corrections issued through ProjectDox; fee set by fee schedule at submittal. Pre-approved plans availability: Program established (under AB 1332) for vendor-submitted preapproved Standard ADU Plans — detached ADUs only, no modifications allowed; as of mid-2026 no vendor plans are listed yet ('NONE AT THIS TIME').
Average ADU rental income in Santa Monica: 1-bedroom units rent for $3,000-$3,700/mo/month, 2-bedroom units for $4,000-$4,700/mo/month. Short-term rentals: No — ADUs/JADUs may not be rented for terms of 30 days or less. Expected ROI: 5-8% annual return.
The minimum lot size for an ADU in Santa Monica is None. 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.