Accessory Dwelling Units (ADUs), also known as granny flats, in-law suites, or second units, offer homeowners a smart way to increase living space and property value in the County of San Diego. Whether you're looking to house extended family, generate rental income, or boost your home’s resale value, ADUs are an increasingly popular and city-supported solution.

This article covers everything you need to know about ADUs in the County of San Diego, including eligibility, permitting, construction requirements, and recent updates as of 2025.

Who Governs ADU Rules in San Diego County?

The County of San Diego Planning & Development Services (PDS) oversees ADU regulations for unincorporated areas, such as Fallbrook, Ramona, Julian, and others. If your property is inside city limits (e.g., San Diego City, Chula Vista, Carlsbad), you’ll need to follow that city's specific ADU code.

Types of ADUs Allowed

The County recognizes two main types of ADUs:

1. Standard ADU (Detached or Attached)
   A full independent unit with its own kitchen, bathroom, and entrance. May be attached or detached from the main house.

2. Junior ADU (JADU)
   A smaller unit (up to 500 sq. ft.) built within the existing primary residence with a separate entrance and kitchenette.

ADU Size Limits – San Diego County

• Detached ADU: Up to 1,200 sq. ft.

• Attached ADU: Up to 50% of the primary residence’s floor area

• JADU: Max 500 sq. ft.

• Minimum Size: No less than 150 sq. ft.

Note: Multiple ADUs may be allowed on multi-family lots, subject to available open space and parking.

Setbacks & Height Requirements

• Front yard: Typically not required to place ADUs here.

• Side and rear yard setbacks: Minimum 4 feet

• Maximum height:

  • One-story ADUs: Up to 16 feet

  • Two-story ADUs (with additional zoning): May go up to 25–30 feet

Parking Requirements

• No parking required if:

  • Located within ½ mile of public transit

  • Within an architecturally historic district

  • Converted from an existing structure (garage, etc.)

• Otherwise, 1 parking space per ADU or bedroom may be required.

Parking can be in tandem, on driveways, or on uncovered spaces.

Permitting Process – County of San Diego

1. Feasibility Review (Optional but recommended)

2. Site & Floor Plan Submission

3. Permit Application through PDS

4. Plan Check

5. Construction & Final Inspection

Average timeline: 3 to 6 months, depending on complexity.

You can apply online via the San Diego County PDS Accela Citizen Portal.

Permit Fees & Costs

Permit and plan check fees vary based on the ADU’s size, location, and utility connections. However, to encourage affordable housing, some ADU Permit Fee Waivers in California have been introduced, and the County has reduced or waived certain development impact fees (DIFs).

• Permit & plan review: ~$3,000–$10,000+

• Construction cost: Typically $150,000–$350,000+

Pre-Approved ADU Plans

To speed up construction and permitting, the County offers free pre-approved ADU floor plans (also known as "permit-ready plans"). These plans meet building code standards and reduce design time.

Financing & Incentives

Homeowners can explore:

• CalHFA ADU Grants: Up to $40,000 for qualifying low- to moderate-income homeowners

• Property Assessed Clean Energy (PACE) loans

• Home equity or construction loans

Some builders, like Fortune ADU, also offer in-house financing assistance.

Green Building & Energy Compliance

All new ADUs must meet Title 24 energy codes. This includes:

• Energy-efficient insulation and windows

• Solar panel requirements for detached new construction

• Water-conserving fixtures

Why Build an ADU in San Diego County?

• Rental income potential: $1,800–$3,000+/month

• Family housing: Multigenerational living without buying a second home

• Property value: Increases by 20%–35%

• Flexible living space: Home offices, studios, guest homes