Important Rules for Building an ADU in San Diego, CA

Building an ADU in San Diego County? Here Are the Key Rules to Know

Whether you want extra rental income, a private space for family, or a long-term investment in your property, understanding the local rules is essential before you start designing.

Below is a simple breakdown of the most important ADU construction rules San Diego County homeowners should know — including eligibility, size limits, setbacks, parking, and permits.

1. CAN YOU BUILD AN ADU ON YOUR PROPERTY?

In most parts of San Diego County, ADUs are allowed on lots with an existing single-family or multi-family home — but your exact rules depend on your city and zoning.

Key things to confirm:

• Zoning and lot type (single-family vs multi-family)

• Property location (some areas fall under special overlays)

• Rental rules (short-term rentals may be restricted depending on the city)

Many homeowners build ADUs for long-term rental or family housing, which is typically the safest and most widely permitted use.

2. HOW BIG CAN YOUR ADU BE?

ADU size rules depend on the type of unit you’re building. San Diego County generally follows California state allowances, but local standards can still affect what is approved.

Typical maximums include:

• Detached ADUs: Up to 1,200 sq ft

• Attached ADUs: Up to 50% of the primary home (max 1,200 sq ft)

• Junior ADUs (JADUs): Up to 500 sq ft within existing space

3. SETBACKS & HEIGHT REQUIREMENTS

Setbacks and height limits are a major part of ADU planning — and they can impact your layout more than most homeowners expect.

Common guidelines include:

• Setbacks: Often 4 ft from side and rear property lines for detached ADUs

• Height limits:

  • One-story: commonly around 16 ft

  • Two-story: can vary widely by city

In some areas (especially coastal zones), height and design restrictions may be stricter.

4. BUILDING CODE & ENERGY REQUIREMENTS

Every ADU must meet California Building Code and Title 24 energy standards, including:

• Safe electrical and plumbing systems

• Ventilation and heating requirements

• Insulation standards

• Fire safety requirements (depending on location and proximity)

New ADUs in California typically require solar panels, unless the project qualifies for a specific exemption.

5. PARKING REQUIREMENTS

Parking rules for ADUs are often easier than homeowners expect, especially under California’s statewide ADU laws.

In many cases, parking is not required if the ADU is:

• Near public transit

• Under 500 sq ft

• A conversion of an existing garage or structure

If parking is required, it’s often one off-street space, and tandem parking is usually allowed.

6. THE ADU PERMITTING PROCESS

San Diego County cities are required to review ADU permit applications quickly once a complete submittal is provided.

Here’s what the process usually includes:

• Submit plans and required documents

• Planning review and corrections (if needed)

• Building plan check approval

• Permit issuance

• Inspections during construction

State law requires ADU applications to be reviewed within 60 days once complete.

FINAL THOUGHTS

Building an ADU in San Diego County can be an excellent way to add value, create more living space, and increase your property’s long-term potential. The key is understanding your local city’s rules early so you can design correctly and avoid delays.