Building an ADU in Santa Monica. Rules, costs, timeline.

Can I build an ADU in Santa Monica?

Five things to know before you start

If you read nothing else on this page, read these. They are the five points that change the most Santa Monica projects.

Number of ADUs per parcel — Santa Monica allows four accessory units on an R1 lot

The Guide allows all of the following on a parcel with a Single-Unit Dwelling, in combination:

On an R1 lot that is four accessory units in addition to your existing house — five dwelling units on the parcel. Outside R1 the attached ADU is not available, so the maximum is three accessory units plus the house, for four in all. Either way it is materially more generous than the state-law floor, which is itself a stack: a conversion ADU, a JADU, and a detached ADU (Gov. Code § 66323(a)(1)–(2)). On multifamily parcels, Gov. Code § 66323(a)(4) (as amended by SB 1211, 2024) independently allows up to eight detached ADUs on a lot with an existing multifamily dwelling.

Owner-occupancy

You do not have to live on the property to build or rent an ADU. Gov. Code § 66315 bars Santa Monica from imposing an owner-occupancy requirement on an accessory dwelling unit. A junior ADU is the one exception — and a narrow one after AB 1154 (effective January 1, 2026), which amended Gov. Code § 66333 so the requirement reaches only a JADU that shares sanitation facilities with the primary home. Give the JADU its own bathroom and owner-occupancy no longer applies. The JADU still records the deed restriction prohibiting separate sale (SMMC § 9.31.025).

What an ADU costs in Santa Monica (2026)

Our Signature plans are fixed-price — architectural design and full permit processing included, the same number whether the lot is in Santa Monica, Culver City, or the Valley. Construction is separate: once your plans are permitted, you build it yourself, bring your own licensed contractor, or build with one of our vetted construction partners. The figures below are the estimated cost to build each model with an independent licensed general contractor. Here is the lineup:

What is fixed is the plan: our Signature plan fees run $7,490 to $12,990 — architectural design and full permit processing included. We can quote it because our Signature Homes were engineered to pass Santa Monica's objective standards in SMMC § 9.31.025 on paper. The build figures above are an estimate by an independent licensed general contractor, roughly $180K–$420K across the lineup — your plans, your choice of builder: build it yourself, bring your own contractor, or use one of our vetted construction partners.

Not in either number: your standard Santa Monica building-permit and plan-check fees (based on valuation, payable directly to the City), utility connection fees (SoCal Edison, Southern California Gas, Santa Monica Water), and — if your parcel is in the Coastal Zone — your CDP processing fee. Your Backyard Review includes a line-item estimate of those pass-through costs for your specific lot.

For sizing and payback math: try our ADU calculator and the ROI calculator.

Development fees

State law (Gov. Code § 66311.5(c)(1)) prohibits impact fees on any ADU under 750 sqft and caps fees on larger ADUs at a share proportional to the primary dwelling. You will still pay standard building-permit and plan-check fees — which are based on project valuation, not on the fact that you are building an ADU — and utility connection fees where required.

What it returns: renting your ADU

Santa Monica blocks short-term rentals (SMMC Chapter 6.20). That sounds restrictive. It actually helps owners.

Long-term rents in Santa Monica are among the highest in LA County. Supply of legal, fully-permitted detached rentals is tight. Tight supply protects pricing.

The trusted benchmark is HUD’s Fair Market Rent for the Los Angeles–Long Beach–Glendale metro area (FY 2026, revised effective May 21, 2026). A new, fully permitted detached ADU in Santa Monica typically rents at or above the metro FMR. Here is how the market breaks down by unit type:

Every Signature Home maps onto these bands — the Melrose rents as a 2-bedroom, the Lincoln as a 3-bedroom. The full lineup with build costs is in the cost table above. For payback math keyed to your specific lot and financing assumptions, use the ADU ROI calculator.

HUD FMR figures: FY 2026 Fair Market Rents, Los Angeles–Long Beach–Glendale HUD Metro FMR Area, as revised effective May 21, 2026 (huduser.gov; Federal Register, Apr. 21, 2026). The Santa Monica rent ranges are estimates drawn from publicly available Santa Monica listings for comparable 30+ day rentals — a typical spread, not an average or an appraisal. They are not a guarantee. Your specific ADU's performance depends on finish level, lot, access, parking, and the rental market at the time you lease it. Ranges reflect typical market variability between a "good" and "very good" Santa Monica micro-location; truly premium blocks (e.g. north of Montana, direct beach-adjacent) can exceed the high end.

Why the Santa Monica market rewards the investment

Between the Coastal Zone overlay, the Chapter 6.20 short- term rental rules, and the rent-control regime, Santa Monica has more regulatory complexity than most LA County jurisdictions. Why build here anyway?

• Two-story, 24-foot detached ADUs by right. SMMC § 9.31.025 is more permissive than state law on detached-ADU height. Most LA-area cities build to the 16/18-ft state floor. Santa Monica gives you the extra story without a variance conversation.
• Four accessory units on an R1 lot — five dwelling units in all. The Guide's combination rule (1 converted + 1 JADU + 1 detached + 1 attached on R1), added to the house already standing, is materially more generous than the state-law floor. That is real density — and real rental yield — on a single-family parcel.
• ADU-as-condo is on the table. SMMC § 9.31.026 gives you a separate-sale exit under AB 1033 that most LA-area cities simply do not offer.
• On-site parking is not required. The ordinance does not impose it. For a Westside lot where every square foot matters, that is worth five figures in design optionality alone.
• Long-term rents are among the highest in the county. The absence of STR supply tightens the long-term rental market, which benefits legal, fully-permitted ADU owners.
• Ministerial approval is real. If the plan meets SMMC § 9.31.025 on paper, the City has no discretion to reject it. No design review, no neighbor appeal path.
• Property values among the most resilient in California. A fully permitted ADU adds square footage that comps directly into resale. In a market where comps are rare because turnover is low, that is real money.
• State law backstops the city. Even when the City is slow on something, Gov. Code §§ 66310–66342 preempts. The 60-day clock under § 66317 runs. The state-mandated minimums apply.

When an ADU isn’t the right move

Not every Santa Monica property is a good ADU candidate, and it is cheaper to learn that now than after you have paid for plans. Four situations where we would tell you to wait, choose a different unit type, or not build at all:

• Your numbers depend on short-term rental income. They will not work. Rentals of 30 days or less are prohibited (SMMC Chapter 6.20), and no ADU carve-out exists. Run the math on a 30+ day tenancy or reconsider the project.
• You need to sell the unit soon. Santa Monica does allow a separate ADU sale under SMMC § 9.31.026 — but a condominium conversion is its own process on top of building the unit. As a fast exit, it is the wrong plan.
• What is left of your lot after setbacks is very small. After the 4-ft side and rear setbacks and the 4-ft separation from the house, some parcels simply cannot take a detached structure worth building. On those lots a garage conversion or a JADU usually delivers more value than forcing a new build.
• You are in the Coastal Zone and need a firm, short timeline. The Coastal Development Permit or Waiver runs on the Coastal Commission’s schedule, not the City’s 60-day ministerial clock. If a hard deadline drives the project, factor that in before you start — it is not something any builder can compress.

The rules that make Santa Monica different

The Coastal Zone

The California Coastal Act (Pub. Resources Code § 30000 et seq.) designates a Coastal Zone along the state's coastline. If your parcel sits inside that zone, the City's ADU Guide states plainly: "if the parcel is within the Coastal Zone, a Coastal Development Permit or Waiver may also be required through the California Coastal Commission." That is the big distinction — coastal review is processed through the California Coastal Commission, not through the City's ministerial ADU approval. The ADU building permit itself remains ministerial. The coastal overlay is separate.

Is my lot in the Coastal Zone?

The zone generally extends inland from the mean high tide line to Lincoln Boulevard, plus portions of Ocean Park and the beachfront blocks. If you are west of Lincoln, assume yes and verify. If you are east of Lincoln, assume no and verify. We confirm the coastal designation for every Santa Monica parcel before we commit to a schedule.

Two pathways: CDP or Waiver

The ADU Guide also calls out parking: "If subject parcel is located within the Coastal Zone, please contact the California Coastal Commission regarding parking requirements." That is the one place Santa Monica's blanket no-parking rule may be subject to Coastal Commission conditions.

Can you Airbnb a Santa Monica ADU?

If your investment thesis depends on short-term rental income, Santa Monica is the wrong city. SMMC Chapter 6.20 (Home-Sharing and Vacation Rentals), first adopted May 12, 2015 and amended through 2019, is the strictest STR ordinance in LA County.

The City's ADU and JADU Guide states the rule in one sentence, repeated on every ADU type (converted, JADU, detached, and R1 attached): "Short-term rentals (30 days or less) are not permitted." There is no carve-out for ADUs. There is no exception for primary residence. An ADU or JADU in Santa Monica is a 30+ day tenancy, full stop.

Citywide, SMMC Chapter 6.20 (Home-Sharing and Vacation Rentals) prohibits vacation rentals outright and permits home-sharing only in a host's primary residence while the host is present. Chapter 6.20 governs the primary home; the ADU Guide governs the ADU. Both point to the same conclusion.

The practical effect: a Santa Monica ADU is a long-term rental asset (30+ day tenancies), a multigenerational space, or a home office / studio. Which is fine, because Santa Monica long-term rents are among the highest in LA County.

Selling your ADU separately — and other recent state-law changes

California ADU law has been amended almost every year since 2017. Santa Monica's ordinance is required to comply with the current state statute even where the City has not formally updated its own text. The five changes that matter right now:

The AB 1033 opt-in deserves the emphasis: most cities have not adopted an ordinance. Santa Monica has — SMMC § 9.31.026 (Accessory Dwelling Unit Condominiums) — and the City's ADU Guide confirms it on both converted ADUs and detached ADUs on SUD parcels, stating the unit is "permitted to be sold separately from the SUD following the standards of SMMC Section 9.31.026." That makes Santa Monica one of the few LA-area cities where an ADU-as-condo exit is actually on the table.