ADU Constructionin Santa Monica, CA
ADU construction in Santa Monica follows SMMC 9.31.025: a studio or one-bedroom ADU may reach 850 square feet and a larger one 1,200, with 4 foot side and rear setbacks and no parking. The City must act on a complete application for a lot with a house within 60 days, though Coastal Zone and historic lots add review.
Santa Monica has few places to put a backyard unit. Only 20.7 percent of its 54,322 homes are detached houses, about 11,242 lots, while 63.7 percent of homes are in buildings of five or more units and 74.6 percent of households rent, according to the 2024 American Community Survey. The town was founded in 1875 and grew from 15,252 people in 1920 to 71,595 in 1950 as Douglas Aircraft drew workers, which left behind small 1940s cottages on long lots in places like Sunset Park.
This page covers how many units the code lets one lot hold, the Coastal Zone, historic districts, garage conversions, plan review, utilities and the rental and sale rules. Regional costs and the statewide law are on our ADU construction page, and our other trades in the city are on the Santa Monica service page.
What the City's ADU code and project tables say about Santa Monica ADUs
Where adu construction permits come from in Santa Monica: City of Santa Monica Community Development Department, Building and Safety Division.
- SMMC 9.31.025 says an ADU or JADU that meets its standards is permitted by right and approved ministerially without a hearing, the City must approve or deny a complete application within 60 days for a parcel with an existing home, and an application not acted on within 60 days is deemed approved. The City may not deny an ADU because of nonconforming zoning conditions or unpermitted structures that are not a threat to health and safety.
- On a single-unit parcel the City allows one converted ADU, one JADU, one detached ADU and one more ADU under the R1 provisions (SMMC 9.31.025(H)). A studio or one-bedroom ADU may be up to 850 square feet and one with more than one bedroom up to 1,200 square feet, with a 150 square foot minimum, and a JADU may be 150 to 500 square feet inside the single-unit dwelling.
- New detached or attached ADUs in SMMC 9.31.025(I) need 4 foot side and rear setbacks, the zoning front setback, and a height of 2 stories or 24 feet for a detached unit. Converting existing space or an existing accessory structure needs no setback and may expand 150 square feet into the front setback for access.
- SMMC 9.31.025(L) and (M) require no parking for an ADU or JADU and no replacement of parking removed for one, and bar renting an ADU or JADU for 30 days or less except as allowed by the home-sharing chapter. Separate sale of an ADU is allowed only to a qualified buyer under Government Code 66340 or the ADU condominium section.
- A new ADU structure or addition of floor area is Medium Plan Review with a 3 week initial review and 2 weeks per resubmittal, and the table lists a soils report for a new or attached ADU adding 750 square feet or more on hillside, seismic or fault-hazard properties. Public Works items include water neutrality, undergrounding of overhead utilities, a Construction and Demolition Waste Management Plan and tree protection where there is no alley access.
- Converting existing floor area to an ADU is Minor Plan Review (five working days). The Fire Department may require sprinklers throughout if the main house already has them or the ADU is more than 150 feet from the primary street address with no rear alley access, and utility undergrounding applies when valuation exceeds 50 percent of the replacement value of existing structures, with waivers.
- Santa Monica's Preapproved ADU Program under AB 1332 lets vendors submit Standard ADU Plans for detached ADUs only, which owners then adapt to the site for expedited review with no modifications to the preapproved plans. The program page says Standard ADU Plans are valid only within the same triennial California Building Standards Code cycle and that ADUs larger than 750 square feet may be subject to Public Works impact fees.
- SMMC 9.07.010 states that the R1 district is meant for one unit plus one ADU and one JADU per parcel.
Build an ADU in Santa Monica: how many units fit on one lot?
The R1 zone requires a parcel of at least 5,000 square feet, 50 feet wide and 100 feet deep, and allows one house plus ADUs. SMMC 9.31.025 lists the combinations on a single-unit lot as one converted ADU, one junior ADU, one detached ADU and one more ADU under the R1 provisions, while the R1 purpose statement speaks of one ADU and one JADU. The two readings differ, so ask Planning which combination your parcel can carry before you pay for plans.
A studio or one-bedroom ADU may be up to 850 square feet and one with more bedrooms up to 1,200, with a 150 square foot minimum. A JADU runs 150 to 500 square feet inside the house. A new detached or attached unit needs 4 foot side and rear setbacks and the zoning front setback, and a detached one may rise to two stories or 24 feet.
State law adds protected types that cities must approve, including one detached unit of up to 800 square feet and, on a lot with an existing multifamily building, up to eight detached units, under Government Code section 66323. Those matter in a city where most homes are apartments.
ADU construction in the Santa Monica Coastal Zone: who issues the permit?
The City says its Coastal Zone takes in much of Downtown Santa Monica, including the Third Street Promenade. A City grant application to the Coastal Commission described the Local Coastal Program as a 1992 Land Use Plan with no Implementation Plan, which means the Coastal Commission, not the City, decides coastal development permits until a full program is certified. A June 1, 2026 City press release says the Council authorized an agreement with the Commission aimed at certification by the end of 2027.
The practical rule is in SMMC 8.08.070: the City may not issue a building permit for work that needs a coastal development permit until that permit exists. State law gives the City or the Commission 60 days to act on the coastal permit for an ADU, and the two reviews run side by side, under Government Code section 66329.
We could not find a page that gives the Coastal Zone boundary or says which ADU types need a coastal permit, so we make no promise about any block. Ask the City, and if the answer is yes, expect the timeline to stretch; the City's own tables warn that Coastal Zone projects may be delayed.
An ADU behind an old bungalow: historic districts and the 50 percent wall test
Five historic districts, designated between 1990 and 2019, and a landmark list numbered through 143 can reach a backyard project: Third Street Neighborhood, Bay Street Craftsman Cluster, San Vicente Boulevard Courtyard Apartments, 11th Street Bungalow and 4th Street Corner. Work on a landmark or a contributing building needs a certificate of appropriateness under SMMC 9.56.070, and the City keeps a Historic Resources Inventory whose buildings face a stricter demolition test.
SMMC 9.25.030 counts a project as a demolition when more than 50 percent of the exterior wall elements are removed or stop being structural over five years. For an inventory building older than 40 years the line is 25 percent of street-facing walls or 50 percent of all walls. A building whose original permit is more than 40 years old also faces a 75-day Landmarks Commission window before a demolition permit can issue.
Accessory buildings under 400 square feet are exempt from that chapter unless they are designated or inventoried, so many one-car garages fall outside it and most two-car garages do not. Ask Planning to read the garage's date and size before a conversion is priced.
Garage conversion ADU in Santa Monica: no setback, no parking and the access addition
Converting existing space or an existing accessory structure needs no setback under SMMC 9.31.025, and the unit may grow by 150 square feet into the front setback for access. The code asks for no parking for an ADU or JADU and for no replacement of the garage spaces a conversion removes. The City treats a conversion of existing floor area as Minor Plan Review, with a five-working-day first review, and a permit application is 100 percent electronic.
Two Fire Department and Public Works items change the budget. Sprinklers may be required throughout the unit if the main house already has them, or if the ADU is more than 150 feet from the primary street address with no rear alley. Utility undergrounding applies when the valuation passes 50 percent of the replacement value of existing structures, though waivers exist.
If a garage was already turned into a room without a permit, the code says the City may not deny an ADU because of unpermitted structures that are not a threat to health and safety. That does not remove the inspection, only the penalty for the past. Our garage conversion permit steps guide shows the build checklist.
How long does ADU plan review take in Santa Monica, and are preapproved plans faster?
A new ADU structure is Medium Plan Review: three weeks for the first review and two weeks for each resubmittal, according to the City's project table, which also says reviews are currently running behind. State law sets separate clocks that apply to the City. It must tell you within 15 business days whether the application is complete, then approve or deny a complete application for a lot with a house within 60 days, or the application is deemed approved.
The City's Preapproved ADU Program under AB 1332 covers detached units only. Vendors file standard plans, owners adapt them to the site, and the plans cannot be modified. They stay valid only inside one triennial building code cycle, and ADUs over 750 square feet may owe Public Works impact fees.
The table also asks for a soils report when a new or attached ADU adds 750 square feet or more on a hillside, seismic or fault-hazard property. County hazard maps show small mapped fault and liquefaction areas inside the city, but only a parcel check settles a given lot.
Utilities, easements and fees on a Santa Monica ADU: what the City does and does not say
The City's ADU tables list Public Works items for a new unit: water neutrality, utility undergrounding, a Construction and Demolition Waste Management Plan and tree protection where the lot has no alley access. A block wall or fence inside a Southern California Edison easement needs authorization through a Request for Easement, and the tables suggest contacting SCE early about overhead line clearances.
On fees, state law bars impact fees on an ADU of 750 square feet or less and on a JADU of 500 or less, and sets proportional fees above that. Utility connection charges are separate from that exemption, and a unit converted from existing space cannot be forced to pay for a new connection. We print no dollar fee because the City's fee schedule was not something we could confirm.
Because 74.6 percent of households here rent, the main house may have tenants. If trenching or a service shutoff could affect them, SMMC 8.100 can require a means and method plan before the permit. Our ADU cost guide explains how those items show up in a proposal.
Renting, selling and short-term use of a Santa Monica ADU
SMMC 9.31.025 bars renting an ADU or JADU for 30 days or less except as the City's home-sharing chapter allows, so a guesthouse used as a nightly rental is a separate legal question. State law does not let a city require owner occupancy for an ADU, and a JADU needs it only where sanitation is shared. Separate sale is allowed only to a qualified buyer under state law or through the City's ADU condominium section.
Whether a newly built ADU falls under Santa Monica rent control is a question we could not settle. The City's fact sheet says most rental buildings built before April 10, 1979 are controlled, along with some built later, and that new tenancies on controlled property must be registered. Ask the Rent Control Board about your parcel before you set a rent.
A new detached ADU must carry solar panels under the state Energy Code, according to the state housing department's handbook, and the State Board of Equalization says new construction is reassessed only on the new portion. Our ADU versus JADU guide compares the two unit types.
ADU details from Santa Monica lots
Three views of the framing, conversion and finishes behind a Santa Monica ADU project. Tap a photo to enlarge it.
What adu construction costs around Santa Monica
The regional ranges on our ADU construction page put a garage conversion at about $100,000 to $200,000 and a new detached unit of 400 to 800 square feet at about $200,000 to $400,000. Those rest on a University of California survey of 2018 and 2019 projects, Remodeling magazine's 2025 figure of $178,536 for a Los Angeles unit and builder quotes, and we rate them medium-low. The City's ADU Handbook says it contains cost estimates, but we could not open it, so we quote none from it. Neighbors write their own rules: see Los Angeles, Glendale and Pasadena. A second unit often comes with other work, so see a room addition in Santa Monica, bathroom remodeling in Santa Monica, window replacement in Santa Monica and concrete work in Los Angeles.
| What it covers | Typical range |
|---|---|
| Garage conversion to a studio or one bedroom | $100,000 to $200,000 |
| New detached ADU, 400 to 800 sq ft | $200,000 to $400,000 |
| UC Berkeley survey, Los Angeles County median, 2018 and 2019 projects | $100,000 overall. $90,000 garage. $180,000 detached. |
| Terner Center and Berkeley CCI, 2020 | $148,000 Los Angeles estimate. $167,000 statewide average. |
| Remodeling Cost vs. Value 2025, Los Angeles | $178,536 job cost |
| Electrical and plumbing, Angi Los Angeles, January 2026 | Electrical $2,600 to $7,800. plumbing $3,900 to $10,400. |
| City permit and plan check fees | Not priced here |
Other work we manage in Santa Monica
Questions about ADUs on Santa Monica lots
How do I build an ADU in Santa Monica?
Start by checking zoning, the Coastal Zone and historic status for your parcel, then choose preapproved or custom plans. Submit through the City's Electronic Plan Review system, since permit applications are paperless. A general contractor can coordinate drawings, permits and the licensed subcontractors, and the City reviews new units as Medium Plan Review and conversions as Minor Review.
What is the maximum size ADU I can build?
In Santa Monica a studio or one-bedroom ADU may reach 850 square feet and one with more than one bedroom 1,200, with a 150 square foot minimum. A JADU is 150 to 500 square feet inside the house. State law separately protects one detached unit of up to 800 square feet with 4 foot setbacks, so ask which route fits your lot.
Do I need to provide parking for my ADU?
No. SMMC 9.31.025 requires no parking for an ADU or JADU and does not require you to replace parking removed for one, which matters for garage conversions. Separate City rules still limit paving in a front setback, and other site rules still apply, so confirm the plan with Planning before you remove a driveway.
Can I build more than one ADU on my property?
Often yes, but the code reads two ways. SMMC 9.31.025 lists one converted ADU, one JADU, one detached ADU and one more under the R1 provisions, while the R1 purpose statement mentions one ADU and one JADU. A lot split can also produce two units in total. Ask Planning to confirm what your parcel allows.
How long does it take to get an ADU permit in Santa Monica?
State law gives the City 60 days to approve or deny a complete application for a lot with a house, or it is deemed approved. The City's own table estimates three weeks for a first Medium Review and two weeks per resubmittal, and warns that reviews are running late. Coastal Zone and historic lots can take longer.
Can I rent my ADU on Airbnb or only long-term?
Only long-term, with a narrow exception. SMMC 9.31.025 bars renting an ADU or JADU for 30 days or less except as the City's home-sharing chapter allows, and we did not read that chapter. Ask the City whether your parcel could ever qualify, and check the Rent Control Board's rules for tenancies in a new unit before you advertise.
Does a Coastal Zone address change an ADU permit in Santa Monica?
It can. The City says the Coastal Zone covers much of Downtown, and until a full Local Coastal Program is certified the Coastal Commission decides coastal permits. The City cannot issue a building permit until a required coastal permit exists. State law gives either agency 60 days to act, so confirm your address and start that review early.
How much does it cost to build an ADU in Santa Monica?
We found no Santa Monica cost study we could verify, so we use regional ranges: about $100,000 to $200,000 for a garage conversion and $200,000 to $400,000 for a new detached ADU. Utility work, soils conditions, historic review and Coastal Zone delays move the total. Our written proposal is the real price.
Do I need a permit to convert my garage into an ADU?
Yes. A conversion of existing floor area is Minor Plan Review under the City's project table, with a five-working-day first review. The conversion itself needs no setback and no replacement parking, but the plans still go through electronic review and the Fire Department may ask for sprinklers. If the garage is over 400 square feet or historic, ask Planning about the demolition rules first.
Tell us about your Santa Monica lot
Send the address or neighborhood, whether a garage or backyard is the starting point and whether anyone rents the main house, and we will plan the site visit around that.