Understanding San Diego County ADU Requirements & Guidelines

If you're a homeowner planning to build an accessory dwelling unit on your property, understanding the San Diego County ADU requirements is the first step to doing it legally and avoiding setbacks. ADUs are increasingly popular in California, but San Diego County has its own zoning rules, size limits, and permitting steps you'll need to follow. In this guide, we'll break down the San Diego County ADU guidelines in plain language so you know exactly what's allowed, what to prepare for, and how to move forward with your project.

Before you can build anything, you need to make sure your property qualifies. San Diego County doesn't allow ADUs on every lot. There are basic zoning and location rules in place. Your property must meet all of the following conditions:

• It is located in the unincorporated areas of San Diego County (not within city limits).
• It is zoned for residential use.
• It has an existing or proposed single-family home on the lot.

San Diego County allows several types of ADUs. The kind you choose will affect design, cost, and required permits. You need to know what you're building before you get started. The main ADU types allowed are:

• Detached ADU: A standalone unit, separate from the main home.
• Attached ADU: A unit connected to the main house but with its own living space.
• Conversion ADU: A unit created from existing space, like a garage or basement.
• Junior ADU (JADU): A unit built inside the existing home, limited to 500 square feet.

Size rules depend on the type of ADU you're building. These limits exist to make sure the unit fits the lot and complies with residential use. Here are the maximum sizes allowed, according to San Diego County's website:

• Detached ADU: Up to 1,200 square feet.
• Attached ADU: Up to 50% of the main home's area, maxing out at 1,200 square feet.
• Junior ADU: Maximum of 500 square feet.

The County controls where on your property you can place the ADU. These rules are based on zoning laws and are required for permit approval. Here are the general zoning and setback standards:

• Minimum Side and Rear Setbacks: 4 feet.
• Front Yard Setback Reduction: Allowed for ADUs under 800 square feet in some cases.
• Maximum Height for Detached ADUs: 25 feet.

Every ADU project in San Diego County requires a building permit. The application process is detailed, and missing documentation can cause delays or rejections. Getting your paperwork in order before submission saves you time and unnecessary fees. These are the standard items you'll need to submit:

• A complete site plan with property lines and ADU location.
• Floor plans and elevation drawings.
• Title 24 energy compliance documentation.
• Stormwater management plan (if applicable).
• Application forms and permit fees.

San Diego County does require parking for ADUs in most cases. However, there are a few exceptions depending on your situation. Make sure you know what applies to your lot before you start construction. The parking rules are:

• One space is required for each ADU.
• Tandem and uncovered parking is allowed.
• No parking is required if the ADU is within ½ mile of public transit.
• No replacement parking is needed if you convert an existing garage.

If your property uses a septic system instead of public sewer, you'll need to go through additional steps. The County has strict rules to ensure your system can handle the added load from an ADU. Here's what you'll need to do:

• Hire a licensed ADU contractor to inspect your existing system.
• Submit a revised OWTS layout to the County.
• Complete percolation testing if needed.
• Upgrade the system if it doesn't meet current capacity standards.

San Diego County previously offered a fee waiver program for ADUs, which helped reduce upfront costs. That program ended on January 9, 2024. Now, all projects moving forward must follow standard permit fee rules. Here's what you need to know:

• Permits Issued Before January 9, 2024: May still qualify for waived fees.
• Permits Not Issued by the Deadline: Full permit fees now apply.
• New ADU Applications: Subject to the current County fee schedule.

Building an ADU in San Diego County can be a smart move, but only if you follow the rules from the start. Skipping steps or misunderstanding requirements will cost you time and money. Take the time to plan correctly, choose the right ADU type, and follow every regulation from zoning to final inspection.

If you're ready to build an ADU and want expert help with design, permits, or construction, 3 Day Kitchen & Bath is here for you. Our ADU contractors San Diego team is here to help get projects approved and completed the right way. Call us today to get started.

An ADU is a self-contained living unit with a kitchen and bathroom, legally allowed for full-time occupancy. A guest house may lack these features and typically can't be rented out independently.

Yes, in most cases, San Diego County allows one ADU and one JADU per residential lot, as long as all building and zoning requirements are met for both units.

Separate utility connections are not always required. In many cases, ADUs can share existing water, sewer, and electric lines with the main residence, depending on site conditions.

Yes, ADUs must match the style and appearance of the main home, including materials, roof slope, and exterior finishes, especially in areas with strict design review.

San Diego County does not allow ADUs to be used as short-term rentals (under 30 days). They must be rented out for long-term residential use to stay compliant.