Building an ADU in Carlsbad

What you can build in Carlsbad

ADUs are allowed in zones that allow single-family, two-family, multifamily and mixed-use homes, as long as there is an existing or proposed home on the lot. The rules are in Carlsbad Municipal Code section 21.10.030, and the city summarizes them in its ADU Info-Bulletin IB-111 (August 2026). An ADU application is a ministerial action, with no discretionary review or public hearing, when it meets the code.

Single-family lots. The basic rule is one attached or one detached ADU, not both, plus one junior ADU (JADU). Under the state's mandatory-approval category, a single-family lot can instead have one ADU converted from the house or an existing accessory structure, one new detached ADU of up to 800 sq ft of interior living space with 4-foot side and rear setbacks, and one JADU.

Two-family and multifamily lots. You can convert non-livable space such as storage rooms, basements and garages into ADUs, up to 25% of the existing units (rounded down, but at least one). Outside the Coastal Zone you can add up to eight detached ADUs to a lot with an existing two-family or multifamily building, or two with a proposed one, but never more than the number of primary units. In the Coastal Zone the city allows up to two detached ADUs on these lots.

Coastal Zone. Check whether your lot is in the Coastal Zone on the city's Coastal Zone map. There, ADUs must also follow the city's Local Coastal Program, and the city says the Local Coastal Program applies if it conflicts with state ADU rules. The latest code amendment (Ordinance CS-506, February 2026) is "pending California Coastal Commission certification for areas inside the coastal zone." Statewide rules are on our California page. [1][2][3]

Size, height and setbacks

Size.

• Detached ADU: up to 1,200 sq ft, depending on lot coverage. A detached ADU over 800 sq ft must meet the zone's maximum lot coverage.
• Attached ADU with new construction: 50% of the existing home's floor area or 1,200 sq ft, whichever is less, but no less than 800 sq ft.
• Converted ADU: must fit inside the existing house or accessory structure and can't exceed the square footage of the house. You may add up to 150 sq ft for getting in and out.
• JADU: up to 500 sq ft of livable space.
• No ADU is subject to a minimum lot size.

Height. A detached ADU is limited to one story and 16 feet. Within a half-mile walk of a major transit stop such as Carlsbad Village Station or Poinsettia Station, it can be 18 feet, plus 2 more feet (20 feet total) to match the roof pitch of the house; see the city's transit station walking-distance maps. On a lot with a multistory two-family or multifamily building, the limit is 18 feet. An ADU above or below a one-story detached garage follows the zone's height limit, two stories combined. An attached ADU can be up to 25 feet (or the zone's height limit for the house, if that is higher), but no more than two stories.

Setbacks. New attached and detached ADUs need at least 4 feet from the side and rear property lines. Front setbacks follow the zone, but they can't stop an 800 sq ft ADU; the city lets such an ADU protrude into the front setback when there is no other way to fit it. A converted garage or accessory structure can keep its existing setbacks, unless it is in the Coastal Zone and affects coastal resources such as geologic setbacks, public views, coastal access or habitat buffers. Garages, patio covers, decks and other accessory uses must meet normal zoning setbacks.

Design. Roof decks are not allowed on ADUs. Except for mandatory-approval ADUs, the ADU's roofing, trim, walls, windows and colors must match the main house. [1][2][4]

Parking

Carlsbad requires one parking space for an ADU. It can be in the setbacks or tandem in your existing driveway. No space is required if the property is:

• within a half-mile walk of a public transit stop, such as Carlsbad Village Station, Poinsettia Station or a bus stop (NCTD has stop locations)
• in a historic district
• an ADU built as part of a proposed or existing house or accessory structure
• within one block of a car share vehicle or dedicated car share lot
• in an area where on-street parking permits are required but not offered to the ADU occupant

JADUs need no parking.

Replacing garage parking. You generally don't have to replace a garage, carport or parking space you remove or convert. The exception is near the coast. The code requires replacement on lots west of the rail corridor, and on lots between the rail corridor and Interstate 5 from Avenida Encinas south to Batiquitos Lagoon. Replacement spaces can be covered, uncovered or tandem, or use a mechanical lift, and can sit in the front, side or rear yard on an improved surface. IB-111 also says uncovered spaces removed in the Coastal Zone must be replaced.

State law and the coast. State law says a city can't require replacement of a garage, carport or uncovered space removed for an ADU, but it also says ADU law doesn't lessen the California Coastal Act. If you are near the coast, confirm with Planning which parking rule applies to your lot. [1][2][5][6]

Fees

The city says permit fees for most ADUs are about $2,000 to $4,000, depending on the square footage. Fees are set in the city's Master Fee Schedule, and you pay all plan check and inspection fees. After you apply, the city emails you when fees are due, and plan review doesn't begin until they are paid.

Impact fees. The city says no impact fees are charged for an ADU under 750 sq ft or for any JADU; state law words the exemption as 750 sq ft or less of interior living space. For a larger ADU, impact fees are proportional to the size of the main house; the city's example is a 1,000 sq ft ADU next to a 2,000 sq ft house paying 50%. Special districts and other agencies, such as school districts, may charge their own fees.

Utilities. A new ADU may need a new utility connection, with connection fees based on its square footage or plumbing fixtures. A converted ADU or JADU, including an expansion of up to 150 sq ft, doesn't need a new connection or pay connection fees. A new sewer lateral may be required; the city says to check with your sewer district.

For typical construction costs see our ADU cost guide. [1][5][7][8][9]

Coastal Development Permits and timeline

Coastal Zone. Most ADUs in the Coastal Zone need a Minor Coastal Development Permit from the Planning Division. Attached ADUs and JADUs generally need only a building permit, with a few exceptions in the code. No public hearing is held; neighbors are notified, and the City Planner decides administratively. The coastal permit must be approved before or together with the ADU building permit. State law requires a coastal development permit for an ADU to be approved or denied within 60 days of a complete application, and no public hearing is required for it.

Deadlines. For an application that is only an ADU or JADU, the city says it will tell you within 15 business days whether the application is complete, and approve or deny it within 60 days after it is complete unless you ask for more time. An ADU that is part of a remodel or a new house follows the timeline of that permit. The city's building permit page says plan check reviews not completed within one year of submittal expire, and renewing then means submitting new plans and paying again.

Pre-approved plans. State law requires a city to approve or deny within 30 days a detached ADU that uses a plan preapproved by that city or another agency in California. See our ADU permit process guide. [1][5][6][10][11]

Garage conversions and junior ADUs

Garage conversions. You can convert a garage or other existing accessory building into an ADU and keep its existing setbacks (with the Coastal Zone exception above). You can add up to 150 sq ft for entry and exit. A detached garage can also be torn down and replaced with an ADU in the same location and dimensions; the city reviews the demolition permit with the ADU and issues both at the same time. Fire sprinklers are required only if they were required for the main house. A new detached ADU needs solar panels unless an existing system on site can serve it. More in our garage conversion guide.

Junior ADUs. One JADU is allowed inside a proposed or existing single-family house or attached garage, and you can add on to the house to build it. It can be up to 500 sq ft and needs an efficiency kitchen and its own entrance. It may share a bathroom with the house, in which case an internal connection is required, and the owner must live in the house or the JADU. No separate water, sewer or power connection is required. You must record a deed restriction barring separate sale of the JADU. See our junior ADU guide.

Not ADUs. A guest house can't have a kitchen or wet bar and can't be rented. The city says park model trailers ("tiny homes" on wheels) are recreational vehicles and can't be used as ADUs, but HCD-certified manufactured homes can. See our tiny house guide. [1][2]

Renting it out or selling it

You don't have to live on the property to have an ADU. An ADU must be rented for at least 30 days, and a JADU for at least 31 days. ADUs and JADUs in the Coastal Zone that got a building permit before January 1, 2020, are exempt from these minimums. Homeowners association rules can't prohibit building or renting an ADU or JADU.

Selling separately. IB-111 says Carlsbad "does not permit separate sales of ADUs" and has not adopted the ordinance needed for ADU condominiums. The municipal code says an ADU may be sold separately only in the limited situations state law allows. HCD reads state law to require cities to allow separate sale of an ADU in one narrow case: a property built by a qualified nonprofit and sold to a low-income buyer with long-term affordability restrictions. If that applies to you, ask Planning.

Lot splits. HCD says SB 9 and ADU law can be used together, and that an SB 9 lot split creates two lots, each eligible for up to two primary units. Confirm how Carlsbad applies SB 9 to your lot with Planning; see our SB 9 guide. [1][2][5]

Pre-approved plans and grants

Carlsbad's ADU Permit Ready Program offers free pre-approved plans for single-story detached ADUs: studio, one-, two- and three-bedroom, in Spanish, Farmhouse and Modern styles. You pick the style closest to your house. The city says the plans save three to six months of design time and about $8,000 to $16,000 in design fees, and qualify for expedited processing and lower plan check fees. Any change to the plans means a full plan review.

As of this review, the program page says the plans "are being updated to meet the 2025 California Building Codes and are currently unavailable," with updated plans anticipated by summer 2026. Ask the Planning Division whether they are available now.

State grant. IB-111 still describes CalHFA's ADU Grant of up to $40,000 for pre-development costs, but CalHFA's ADU page says "The latest round of ADU funding has been fully allocated" (December 28, 2023). See our ADU financing guide. [1][7][9][10][12]

Permit steps in Carlsbad

1. Check your lot

   Find your zone and whether you're in the Coastal Zone or within a half-mile walk of a transit station, and read IB-111. Check with city staff before you submit if your site needs other work, such as a retaining wall. [1][3][4]

2. Prepare plans

   Have a site plan with setbacks, lot coverage, parking, heights, grading and utility connections prepared, or use the city's Permit Ready plans with the B-75 checklist when they are available. [9][10]

3. Get a Minor Coastal Development Permit if needed

   In the Coastal Zone, submit the Land Use Application (P-1) and Minor Coastal Development Permit supplemental form to Planning. It must be approved before or together with the building permit. [1][10]

4. Apply for the building permit

   Submit the Residential Building Permit Application (B-1) with your plans through the online permit portal if the permit type is offered there, by email to buildingsubmittals@carlsbadca.gov, or in person by appointment. [1][7][8]

5. Pay fees and respond to plan check

   The city emails you when fees are due; review starts after payment. Plans are routed to city divisions, and you resubmit until all corrections are addressed. [8][11]

6. Get the permit, build and pass inspections

   For a JADU, record the required deed restriction. Schedule inspections with the Building Division at 442-339-2700. [2][7]

Pre-approved and sample plans

• ADU Permit Ready Program

  Free pre-approved single-story detached ADU plans (studio to three bedrooms, three styles); the city says they are being updated for the 2025 building codes and are currently unavailable. [1][10]

Who to call

• City of Carlsbad Building & Permits

  ADU building permits and plan check (inspections: 442-339-2700; 1635 Faraday Ave., Monday-Friday 8 a.m.-5 p.m.)

  442-339-2719

  1635 Faraday Ave., Carlsbad, CA 92008

  [7][11]

• City of Carlsbad Planning Division

  Zoning questions, Minor Coastal Development Permits and the ADU Permit Ready Program

  442-339-2610

  [1][10]

Questions people ask