ADU Constructionin San Diego, CA
ADU construction in San Diego runs on state law and the City's Information Bulletin 400, which allows one ADU, one converted ADU and one junior ADU on a single-dwelling lot, with ADUs from 150 to 1,200 square feet. A bonus program can add more units. Coastal and fire-zone lots add approvals. Confirm your lot with the Development Services Department.
San Diego has more renters than owners, and a second unit serves that market. The Census Bureau's 2024 one-year estimates count 588,866 homes, with 53.5 percent of the 542,590 occupied homes renter-occupied, 42.5 percent of all homes single-family detached (250,408) and 38.2 percent in buildings of five or more units. Wikipedia's census table shows the city growing from 147,995 people in 1930 to 333,865 in 1950, and it says later growth annexed large areas to the north for suburbs. The median owner-occupied home is worth $980,700, so an ADU is a serious money decision as well as a building one.
This page covers how many units one lot can hold, the City's bonus program, coastal and fire-zone limits, garage conversions, renting and selling, and the order of the job. San Diego publishes its rules in Information Bulletin 400 and on the Development Services pages, and the City's pages and its code disagree in places, so we flag them. Price ranges and phases are on our ADU construction page.
San Diego Development Services rules that apply to ADU construction
Where adu construction permits come from in San Diego: City of San Diego Development Services Department (DSD).
- DSD Information Bulletin 400 (January 2026) defines an ADU as 1,200 square feet or less with complete independent living facilities, and allows on a single-dwelling lot one primary home, one attached or detached ADU, one converted ADU and one JADU. On a lot with an existing multi-unit building it allows up to eight detached ADUs (not more than the existing unit count) plus conversions of non-habitable space up to 25 percent of the existing units, and on a proposed multi-unit building up to two detached ADUs.
- Per IB 400 an attached or detached ADU must be at least 150 and no more than 1,200 square feet, a conversion of an existing accessory structure or part of the home is not subject to the 1,200 square foot cap, and one ADU up to 800 square feet can be built even if it pushes the lot over the zone's floor area ratio. A JADU must be 150 to 500 square feet inside an existing or proposed single-dwelling home or an attached garage.
- IB 400 setbacks: a new or addition ADU observes the zone's front yard setback (one ADU of 800 square feet or less may encroach into it) and the street side setback or 4 feet, whichever is less, but may go up to the side and rear property lines unless building code fire separation applies. If the ADU is over 16 feet tall and the neighbor is residential it needs a 4 foot side and rear setback, and in a Very High Fire Hazard Severity Zone it needs at least 4 feet regardless of height, with the Fire Code Official able to require more near brush management zones.
- IB 400 says no parking is required for an ADU outside the Coastal Overlay Zone; inside it, one space is required only in the Beach Impact Area of the Parking Impact Overlay Zone outside a transit priority area, with exceptions for ADUs of 500 square feet or less, attached ADUs, historic district lots, permit parking districts and lots within one block of a car share vehicle. Garage or carport conversion does not require replacement parking outside that case.
- San Diego lets ADUs be sold separately as condominiums under Municipal Code 141.0302(f) when the City's conditions are met, such as Davis-Stirling and Subdivision Map Act compliance, lienholder consent and a recorded covenant to offer the unit for at least 30 days to owner-occupant buyers; ADUs with San Diego Housing Commission financing or rent restrictions cannot be sold separately while the restriction lasts. The owner does not have to live on site and rentals must run at least 31 consecutive days.
- IB 400 says an ADU needs automatic fire sprinklers only if the primary home has them, and a detached ADU does not by itself force sprinklers into an existing home, but every Affordable ADU and Bonus ADU in the ADU Home Density Bonus Program must be sprinklered. A newly built detached ADU must meet the California Energy Code solar requirement, while conversions and additions are not subject to it.
- The ADU Home Density Bonus Program in IB 400 does not allow Bonus ADUs in base zones RS-1-1 through RS-1-4, RS-1-8 through RS-1-11 unless the lot is in a High or Highest Resource CTCAC Opportunity Area, and in a Very High Fire Hazard Severity Zone the lot must front an improved public street with at least two evacuation routes, with no bonus ADUs on cul-de-sacs or lots with a single point of access. Single-dwelling lots are capped at 4, 5 or 6 total ADUs and JADUs by lot area (8,000 square feet or less, 8,001 to 10,000, over 10,000), counting lot area outside environmentally sensitive lands.
- Bonus program ADUs also carry a San Diego Housing Commission agreement and deed of trust recorded before the first permit, one off-street parking space per Affordable or Bonus ADU outside a Transit Priority Area, a minimum of one tree plus two trees per 5,000 square feet of lot, and a Community Enhancement Fee based on the floor area of the Affordable and Bonus ADUs, with some deed-restricted units in High Resource areas excluded from the fee base.
Sources for these rules
How many ADUs can one San Diego lot have, and how big can they be?
Information Bulletin 400, the City's January 2026 ADU handout, defines an ADU as 1,200 square feet or less with complete independent living facilities. A single-dwelling lot may hold the primary home, one attached or detached ADU, one converted ADU and one junior ADU. On a lot with an existing multi-unit building the bulletin allows up to eight detached ADUs, never more than the existing unit count, plus conversions of non-habitable space up to 25 percent of the existing units. A proposed multi-unit building may add up to two detached ADUs.
Size has a floor and a ceiling. An attached or detached ADU runs from 150 to 1,200 square feet, a conversion of an existing structure or part of the home escapes the 1,200 square foot cap, and one ADU of up to 800 square feet can be built even when it pushes the lot past the zone's floor area ratio. A JADU is 150 to 500 square feet inside an existing or proposed home or an attached garage. State law backs the floor: a city cannot cap an ADU below 850 square feet, or 1,000 with more than one bedroom, and must allow 800 square feet with 4 foot setbacks.
What is San Diego's ADU Home Density Bonus Program, and what does it require?
It is a City program, run with the San Diego Housing Commission, that lets some lots build more units than the base ADU rules allow. Single-dwelling lots are capped at 4, 5 or 6 total ADUs and JADUs, depending on whether the lot is 8,000 square feet or less, 8,001 to 10,000 or larger, counting only lot area outside environmentally sensitive lands. Bonus ADUs are not allowed in base zones RS-1-1 through RS-1-4 and RS-1-8 through RS-1-11 unless the lot is in a High or Highest Resource CTCAC Opportunity Area.
The conditions are real obligations. A Housing Commission agreement and deed of trust must be recorded before the first permit, each Affordable or Bonus ADU needs one off-street parking space outside a Transit Priority Area, and the lot needs at least one tree plus two trees per 5,000 square feet. A Community Enhancement Fee is based on the floor area of the Affordable and Bonus ADUs, with some deed-restricted units in High Resource areas left out of the base, and every one of these units must be sprinklered.
In a Very High Fire Hazard Severity Zone the lot must front an improved public street with at least two evacuation routes, and no bonus ADUs go on cul-de-sacs or lots with a single point of access. We did not read the zoning chapter, so ask DSD whether your base zone qualifies. A deed-restricted unit is a long commitment, so read the agreement before you sign.
Can you build an ADU in San Diego's Coastal Overlay Zone, and which rules apply?
Yes, with a coastal answer first, and the rules there trail the rest of the city. Bulletin 400 says the Coastal Commission certified the City's Housing Action Package 1.0 ADU rules on September 12, 2024, but later amendments, including 2025 ordinance O-21989, apply in the Coastal Overlay Zone only after the Commission certifies them. DSD's regulatory updates page says the 2025 ADU amendments took effect August 22, 2025 outside the Coastal Zone. Which version governs a coastal lot is a question for DSD.
Municipal Code 126.0704(a)(9) says an ADU or JADU that is not wholly inside the existing home, or that adds habitable area or converts non-habitable space, cannot use the coastal permit exemption. A detached cottage on a coastal lot therefore needs a Coastal Development Permit from the City or, where the lot sits in its permit jurisdiction, from the California Coastal Commission. State law tells both to act within 60 days, alongside the building review. We could not open the coastal maps, so which blocks fall in which category is a DSD question.
Parking differs on the coast. Outside the Coastal Overlay Zone no parking is required for an ADU. Inside it, one space is required only in the Beach Impact Area of the Parking Impact Overlay Zone outside a transit priority area, with exceptions for ADUs of 500 square feet or less, attached ADUs, historic district lots, permit parking districts and lots within one block of a car share vehicle.
Can you build an ADU on a San Diego canyon lot or in a Very High Fire Hazard zone?
Often, with extra checks. The City adopted the State Fire Marshal's 2025 map by Ordinance O-21992, effective August 30, 2025, with additional areas of its own, and KPBS reported in January 2026 that the zones cover roughly two-thirds of the city, naming Scripps Ranch, Carmel Valley and parts of downtown, Bankers Hill and Hillcrest. That share is KPBS's figure, not the City's, so check the parcel on the City's map. In a Very High zone Bulletin 400 requires ADU setbacks of at least 4 feet whatever the height, and the Fire Code Official can ask for more near brush management zones.
The City's WUI Code, effective February 28, 2026, sets a 30 foot default building setback in the Wildland-Urban Interface Area, with reductions for non-combustible walls, hardscape, fewer windows or higher fire ratings, and its Zone 0 covers the first 5 feet around a structure. The 2026 Land Development Code update also clarifies that the fire code can require a defensible space buffer larger than a base-zone setback.
Canyon lots add a separate gate. DSD warns that residences next to canyons are highly likely to have environmentally sensitive land conditions, and those can require a Neighborhood or Site Development Permit before grading. A recorded brush management easement from the original approval may also limit where a pad can go.
Garage conversion ADU in San Diego: Rapid Review, parking and the sprinkler question
A garage with a kitchen and a bathroom becomes a dwelling, and DSD inspects it like one. A conversion is not subject to the 1,200 square foot cap, and Bulletin 400 requires no replacement parking for a garage or carport conversion outside the coastal case above. Rapid Review, DSD's no-added-cost fast lane for eligible minor projects, lists garage conversions and interior remodels, and its weekly queue on November 6, 2026 showed about 3 business days for issuance.
Sprinklers hinge on the main house. The bulletin requires them in the ADU only if the primary home has them, and a detached ADU does not by itself force sprinklers into an existing home. A newly built detached unit must meet the Energy Code solar requirement, while conversions and additions do not. If the new use leaves a driveway curb that no longer meets City standards, the driveway must be closed to the City Engineer's satisfaction.
Old garages carry the 45-year question. A permit application for work on a garage that old also has to carry a photographic survey of the building and the Assessor's building record, the City's permit page says. Our garage conversion permit steps guide shows the build order, though it describes Los Angeles rules, not San Diego's.
Renting, selling and fees: what San Diego allows for a finished ADU
San Diego does not require the owner to live on the property, and the City's bulletin says rentals must run at least 31 consecutive days. Short-term rentals are a separate question that we did not research.
The City also has a condominium path that state law leaves to each city. Under Municipal Code 141.0302(f) an ADU can be sold separately when the City's conditions are met: Davis-Stirling and Subdivision Map Act compliance, lienholder consent and a recorded covenant to offer the unit for at least 30 days to owner-occupant buyers. ADUs with Housing Commission financing or rent restrictions cannot be sold separately while the restriction lasts.
On fees, state law exempts an ADU of 750 square feet or less from impact fees and counts a unit under 500 square feet as adding no assessable school space, while utility connection charges are separate. DSD's fee schedule is a document we did not open, so no fee amounts are printed here. Refuse, organic waste and recycling storage under Municipal Code 142.0801 also applies to ADU development.
How long does it take to build an ADU in San Diego, from application to final?
Two clocks apply. State law gives the City 15 business days to call an application complete and 60 days after that to approve or deny it when a house already stands on the lot, and silence past 60 days counts as approval. DSD's weekly timeline showed about 7 business days for a Building Permit on November 6, 2026, but the City calls that an estimate that moves with volume and with how complete the submittal is. Applications go in online through a DSD account, as PDFs that meet the City's upload rules.
After issuance, a building permit for a one- or two-family property expires three years later and goes void if an inspection has not validated substantial work within 12 months or if work stops for 180 days. A detached unit is usually a slab and a framed shell, so the order runs plans and survey, utilities, foundation, framing, roofing and windows, rough trades, insulation and drywall, finishes and the final.
On a unit like this MDG Builders, CSLB #1040337, serves as the general contractor: we draw or adapt the plans, handle the DSD portal and manage the sequence, and licensed foundation, framing, plumbing and electrical firms do the building. Our ADU versus JADU guide compares the two unit types.
ADU photos from San Diego and nearby homes
ADU scenes tied to San Diego, from garage conversions and slabs to finished cottages on coastal and canyon lots. Tap a photo to enlarge it.
What adu construction costs around San Diego
Our ADU construction page puts a garage conversion to a studio or one bedroom 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. Three independent sources sit behind those ranges, and none is a San Diego quote. A UC Berkeley survey of owners who finished or applied for an ADU in 2018 and 2019 found a Los Angeles County median of $100,000. The Terner Center estimated $148,000 for Los Angeles in 2020. Remodeling magazine's 2025 Cost vs. Value report lists a Los Angeles ADU at $178,536, with about 39.9 percent recovered at resale. San Diego costs may differ, and the median owner-occupied home here is worth $980,700. A written proposal shows permit, plan check and utility connection charges as separate lines. The ADU cost guide explains how the ranges were built, and the room addition versus ADU guide helps you choose between an attached room and a separate unit. For other approaches see ADU construction in Chula Vista, Carlsbad and Los Angeles. A bath for the unit is on the San Diego bathroom page, a larger attached project on the San Diego room addition page, windows on the San Diego window page, and the San Diego area page lists every trade we cover in the city.
| 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 |
San Diego ADU questions, answered
How do I build an ADU in San Diego?
Check Information Bulletin 400 and your parcel's overlays, choose between a conversion, an attached unit or a detached one, and file online with the Development Services Department, then build under inspection. Every ADU needs a building permit. Coastal and fire-zone lots add steps, and a lot can use the bonus program only if its base zone qualifies.
How big can an ADU be in San Diego?
An attached or detached ADU runs from 150 to 1,200 square feet under Bulletin 400, and a JADU from 150 to 500. A conversion is exempt from the 1,200 foot cap, and one ADU up to 800 square feet can exceed the zone's floor area ratio. State law bars any cap below 850 square feet, or 1,000 with more than one bedroom.
How much does it cost to build an ADU in California?
Sourced ranges are roughly $100,000 to $200,000 to convert a garage and $200,000 to $400,000 for a new detached unit of 400 to 800 square feet. Both come from Los Angeles County studies and a 2025 job cost, not from San Diego, so only a written proposal after a site visit gives your figure.
Do I need to provide parking for my ADU?
Usually not. Bulletin 400 requires no parking outside the Coastal Overlay Zone, and inside it only in the Beach Impact Area of the Parking Impact Overlay Zone outside a transit priority area, with exceptions for small and attached units. A garage conversion needs no replacement parking. Bonus program units need one off-street space outside a Transit Priority Area.
What is the difference between an ADU and a JADU?
An ADU is a complete, independent home of 150 to 1,200 square feet that can be attached, detached or converted. A junior ADU is 150 to 500 square feet inside an existing or proposed single-dwelling home or its attached garage. A single-dwelling San Diego lot may hold one attached or detached ADU, one converted ADU and one JADU.
Do I have to live on the property to build or rent an ADU?
No. San Diego's bulletin says the owner does not have to live on site, but rentals must run at least 31 consecutive days. Short-term rental rules are separate and we did not research them. A JADU can carry its own deed restriction, so read the recorded terms before you rent it.
How long does it take to get an ADU permit?
Under state law the City has 15 business days to judge an application complete, then 60 days to approve or deny it, and a missed deadline means deemed approval. DSD's weekly timeline showed about 7 business days for a Building Permit on November 6, 2026, an estimate that varies. Coastal and historic reviews add time.
Can I sell my ADU separately in San Diego?
Sometimes. Municipal Code 141.0302(f) allows an ADU to be sold as a condominium when conditions are met, including Davis-Stirling and Subdivision Map Act compliance, lienholder consent and a recorded covenant to offer it to owner-occupant buyers for 30 days. Units with Housing Commission financing or rent restrictions cannot be sold separately while those last.
Tell us about your San Diego ADU plans
Tell us the neighborhood, whether the lot is coastal, flat or on a canyon edge, whether you are weighing the garage or the back yard and whether the bonus program interests you, and we will plan the first visit around those answers.