What is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit located on the same lot as a primary residence. These units can be detached, attached, or created through conversions of existing structures like garages or basements. To legally build or convert an ADU, obtaining an ADU permit from the local building authority is typically required. A Junior ADU (JADU) is a smaller unit, up to 500 square feet, entirely within the existing home and can share facilities like bathrooms with the main house.

ADU Types & Size Regulations

Detached ADUs

• Maximum Size: 1,200 square feet

• Height Limit: 24 feet (up to two stories)

• Setbacks: Minimum 4 feet from side and rear property lines

• Lot Coverage: Units up to 800 sq ft are exempt from lot coverage requirements

Attached ADUs

• Size Limit: Up to 50% of the primary dwelling's size, not exceeding 1,200 sq ft

• Minimum Size: 800 sq ft

Junior ADUs (JADUs)

• Maximum Size: 500 square feet

• Location: Must be within the existing home

• Facilities: Can share bathrooms with the main house

Permitting & Construction Requirements

• Zoning: ADUs are permitted on residentially zoned properties with an existing single-family dwelling.

• Permits: A building permit is required to ensure compliance with zoning, building, and health and safety codes.

• Setbacks: ADUs must adhere to front and exterior side yard setbacks, with a minimum side and rear setback of at least 4 feet, except for required fire setbacks.

• Design Standards: The exterior of the ADU must incorporate features similar to the primary dwelling, including roofing, trim, walls, windows, and color palette.

Financing & Incentives

ADU Finance Program

The San Diego Housing Commission (SDHC) offers financial assistance for homeowners building ADUs:

• Loan Amount: Up to $250,000

• Interest Rate: 1% fixed for construction loan; 4% fixed for permanent loan

• Eligibility: Homeowners with incomes up to 150% of the Area Median Income (AMI)

• Affordability Requirement: ADUs must remain affordable for seven years, with rents at or below 80% of AMI

Impact Fee Waivers

State law (SB13) waives impact fees for ADUs under 750 sq ft, including Junior ADUs. Units larger than 750 sq ft have capped fees to reduce financial burdens on homeowners.

Parking Regulations

• No Parking Required: For ADUs located within a half-mile of public transit, in historic districts, or converted from existing spaces.

• Parking Location: If required, parking can be located within setbacks or in existing driveways as tandem parking.

ADU Eligibility Checklist

To determine if you're eligible to build an ADU:

• Location: Property must be in the unincorporated areas of San Diego County.

• Zoning: Property must be residentially zoned.

• Existing Dwelling: Property must have an existing or planned single-family dwelling.

Step-by-Step ADU Construction Process

1. Pre-Design Consultation: Engage with a professional to assess feasibility and design options.

2. Permit Application: Submit required documents, including site plans and structural details.

3. Approval & Fees: Obtain necessary approvals and pay applicable fees.

4. Construction: Commence building, adhering to approved plans and regulations.

5. Final Inspection: Schedule an inspection to ensure compliance with all codes.