ADU Construction Guide for San Diego: 2026 Costs, Permits and Timeline

An accessory dwelling unit can create an independent home for relatives, a long-term rental, a private caregiver suite, or flexible space. But an ADU is not simply a backyard room — it is a legal dwelling with a kitchen, bathroom, and sleeping and living facilities, so it must satisfy zoning, building, energy, fire, utility, and inspection requirements.

For 2026 planning in San Diego, potential budgets range from about $50,000–$100,000 for a limited junior ADU or interior conversion, $90,000–$180,000 for many garage conversions, $180,000–$350,000+ for attached new construction, and $250,000–$500,000+ for a detached ADU. Site access, slope, utility capacity, coastal or fire-zone requirements, size, and finish level can move a project outside these ranges.

Those figures are not quotes or guaranteed averages. Some published prices cover only construction, while others include plans, permits, site work, and utility upgrades. A useful ADU budget must define what "all-in" means before comparing totals. This guide focuses primarily on properties within the City of San Diego; other cities and unincorporated County areas use their own procedures — confirm the authority for the project address before applying any rule or cost.

San Diego ADU Construction at a Glance

Rules vary by property. Easements, environmental constraints, coastal status, fire severity, brush management, historic resources, and the California Building Standards Code can change what is feasible. Use the City's Zoning and Parcel Information Portal (ZAPP) and a property-specific feasibility review before you design.

What Is an ADU?

The City defines an ADU as an attached or detached residential dwelling of no more than 1,200 square feet that provides permanent facilities for living, sleeping, eating, cooking, and sanitation, on a lot with a proposed or existing primary dwelling. An ADU differs from a guest room, office, or recreational structure because it is an independent legal dwelling. A structure without a complete kitchen or sanitation facilities may fall into another building category and follow different rules.

What Is a JADU?

A junior accessory dwelling unit is generally 150–500 square feet within an existing or proposed single dwelling or attached garage. It requires a separate exterior entrance and an independent kitchen or efficiency kitchen, and it may have its own bathroom or share sanitation with the primary residence. San Diego requires a JADU agreement before permit issuance, and owner-occupancy rules are more nuanced for JADUs than for standard ADUs — the City's January 2026 bulletin states an owner generally must live in one of the on-site units when a JADU exists, with specific exceptions. Confirm the current agreement and project facts with the City.

ADU Types and 2026 Costs

How Many ADUs Are Allowed in San Diego in 2026?

The answer depends on zoning, existing buildings, and whether the project uses the City's ADU Home Density Bonus Program. For a typical property in a single-dwelling-unit zone, the City's January 2026 Information Bulletin 400 describes the potential for:

• one primary dwelling;
• one ADU attached to or detached from the primary dwelling;
• one ADU converted from eligible existing space in the primary dwelling or an existing accessory structure; and
• one JADU.

That is more permissive than older "one ADU plus one JADU" guidance — but it does not mean every lot can physically or legally accommodate all units. Floor-area ratio, building and fire code, utilities, access, and other development standards still apply. Properties with existing multiple-dwelling structures follow different rules, and bonus-program projects add affordability, lot-area, fire, parking, landscape, agreement, and fee requirements. Get a property-specific feasibility review before deciding how many units to design.

ADU Size, Setback and Height Rules

Size Limits

Attached and detached ADUs are generally 150–1,200 square feet of interior livable space; JADUs are generally 150–500 square feet. Floor-area ratio and zone limits may affect larger units, though the City also identifies protections that can allow one ADU of up to 800 square feet even where floor-area ratio would otherwise be exceeded, subject to the applicable rules.

Setbacks Are Not Always a Universal Four Feet

Many pages claim every detached ADU must sit four feet from the rear and side lines. San Diego's current rule is more detailed. For a newly constructed ADU, encroachment into side and rear setbacks — potentially up to a property line — may be possible in some circumstances. However:

• an ADU over 16 feet high next to residentially zoned property generally must observe the applicable four-foot or base-zone setback;
• properties in a Very High Fire Hazard Severity Zone must generally observe at least four-foot side and rear setbacks regardless of height;
• the California Building Standards Code may require greater separation, protected openings, or fire-rated construction;
• the Fire Code Official may require additional setbacks; and
• brush-management conditions can require more space.

An existing structure converted to an ADU may generally continue to observe its existing setbacks, and same-location, same-dimension demolition and reconstruction may receive specific treatment. Verify the exact conditions before relying on an existing footprint.

Front Yards and Height

New ADUs generally follow the base zone's front setback, though the City allows a maximum of one ADU of 800 square feet or less to encroach into the front setback under specified rules. Do not treat "16 feet maximum" as a universal height rule — 16 feet is an important threshold for setback treatment, but allowable height depends on zone, location, adjacent use, fire conditions, and project type. Second-story and taller ADUs require property-specific zoning and structural review.

ADU Parking Requirements

The City generally requires no ADU parking outside the Coastal Overlay Zone. Within it, parking is usually not required unless the property is in the Beach Impact Area of the Parking Impact Overlay Zone and outside a transit priority area — and even then, exemptions may apply for units 500 square feet or less, attached units, designated historic districts, residential permit-parking districts, or proximity to a car-share vehicle.

Converting or demolishing a garage, carport, or covered parking structure generally does not require replacement parking, with a limited coastal Beach Impact Area exception. But do not assume an unused driveway curb can remain after a garage conversion — if the project causes the driveway to stop complying with City standards, the curb cut may need to be closed.

Coastal, Fire and Site Constraints

Coastal Overlay Zone

Coastal properties require additional screening, and some ADU regulations are not yet effective within the Coastal Overlay Zone. A Coastal Development Permit may be required when the ADU is not entirely within the existing primary structure, increases habitable area, or converts non-habitable space. Some qualifying JADUs may be exempt.

Fire Hazard and Brush Management

Very High Fire Hazard Severity Zones can affect setbacks, access, materials, and the Bonus ADU Program. The fire official may require greater separation, and sites within brush-management areas can face additional development constraints.

Slope, Drainage, Easements and Historic Review

A buildable-looking backyard can contain sewer, water, drainage, or utility easements, and slope may require grading, retaining walls, shoring, or specialized foundations. A survey and early civil or geotechnical input can prevent designing a unit that is too expensive or cannot occupy the intended location. Historic review or community-specific rules can also affect design and schedule — do not rely on a generic online statement for a particular property.

What Should an "All-In" ADU Budget Include?

The most common budgeting error is comparing a construction-only price with a full-project proposal. A complete budget generally covers:

• Feasibility & due diligence: zoning research, records review, site measurement, utility investigation, and a preliminary layout.
• Survey, soils & engineering: boundary or topographic survey, geotechnical report, civil engineering, structural calculations, and energy documentation as needed.
• Design & plans: site, floor, and roof plans, elevations, sections, structural details, and Title 24 energy calculations. Preapproved plans reduce repeated design work but do not eliminate site adaptation.
• Permit & agency fees: plan check, inspections, MEP permits, school fees when applicable, development impact fees, and water/sewer review — per the City's current fee bulletins.
• Site work & utilities: often the least predictable category — demolition, grading, trenching, sewer and water connections, stormwater, electrical service upgrades, and access restoration.
• Vertical construction & finishes: foundation, framing, roofing, windows, insulation, drywall, cabinets, counters, appliances, fixtures, flooring, lighting, HVAC, and paint.
• Contingency: 10%–15% is a practical starting point; older structures, garage conversions, steep sites, or uncertain utilities may justify more.

San Diego ADU Permit Process: Step by Step

ADU Construction Timeline in San Diego

A detached custom ADU may require approximately 10–18 months from early feasibility through final approval. Straightforward conversions can be faster, while coastal, hillside, utility-intensive, or highly customized projects can take longer. Some phases overlap, so the table should not be added mechanically.

Utility and Energy Planning

Sewer, Water and Electrical Service

Confirm the sewer location, elevation, capacity, and path before finalizing the floor plan — a long route, inadequate slope, hardscape, retaining walls, or an uphill connection can materially change the budget. The permit process includes water-meter information, and existing service and meter capacity must be evaluated against the project rather than assumed. An all-electric ADU adds cooking, water-heating, HVAC, and general loads, so have a qualified professional calculate existing service capacity early; panel or service upgrades and utility coordination can affect both price and schedule.

Solar and Title 24

New, non-manufactured detached ADUs are generally subject to California Energy Code solar requirements, and the panels may be installed on the ADU or the primary dwelling. Conversions within existing space and certain additions are generally treated differently. Every project also needs current Title 24 energy-compliance documentation.

Can You Rent or Sell a San Diego ADU?

The City states that a standard ADU cannot be leased for fewer than 31 consecutive days — do not build a financial projection on nightly or weekend rentals. The City now provides a path for qualifying ADUs to be subdivided as condominiums and sold separately, but it is not automatic: it requires compliance with zoning, subdivision, mapping, lender-consent, inspection, and utility-notification requirements, and certain financed or deed-restricted affordable ADUs cannot be sold separately during the restriction period.

Rental income and resale effects depend on unit size, privacy, parking, location, operating expenses, financing, taxes, and market conditions. Use current comparable long-term rentals and consult appropriate tax, lending, and real-estate professionals rather than a generic return-on-investment percentage.

Common ADU Planning Mistakes

How to Compare ADU Contractor Proposals

Ask each contractor to price the same drawings and written scope, and confirm whether the proposal includes:

• Feasibility and zoning review; survey, soils, civil, and structural engineering.
• Architectural plans and Title 24 calculations.
• Permit administration and government fees.
• Utility applications, trenching, and connections.
• Demolition, grading, and site access.
• Foundation and structural system; solar, HVAC, water heating, and electrical-service work.
• Cabinets, countertops, flooring, fixtures, and appliances.
• Landscaping and hardscape restoration; cleanup, warranties, and final-inspection coordination.
• Allowances, exclusions, change-order procedure, and a milestone-based payment schedule.

Verify the contractor's license through the California Contractors State License Board. California home-improvement contracts should be detailed and written, and CSLB states the down payment generally cannot exceed $1,000 or 10% of the contract price, whichever is less.

Frequently Asked Questions