In unincorporated San Diego County, ADU and addition permits depend on your zoning, unit type, and lot. You’ll need detailed site plans, architectural drawings, and setback and height information, plus potential environmental or septic documents. Detached ADUs can be up to 1,200 sq ft; JADUs up to 500 sq ft; attached units have their own size rules. Expect a 60‑day target for approvals after a complete application. If you keep exploring, you'll uncover key steps and timelines in detail.

ADU Eligibility and Zoning in Unincorporated San Diego County

In unincorporated San Diego County, ADU eligibility and zoning hinge on whether your lot is residential and how you plan to use the space.

If your property is zoned for residential use with an existing or proposed single-family dwelling, you’re eligible for one detached ADU, and you can convert permitted spaces within an accessory structure or the dwelling itself. A junior ADU is also permitted alongside a detached ADU on single-family lots.

For multifamily sites, residential zoning allows two detached ADUs or space-conversions, with height and conversion limits.

You’ll face overlay and fire-zone considerations that affect feasibility. Understand ADU financing options early, and anticipate zoning compliance challenges to avoid delays or redesigns.

Size Limits and Unit Types for ADUs

Size limits for ADUs are defined clearly, with different caps depending on whether the unit is detached, attached, or a JADU.

You’ll find that detached ADUs can reach up to 1,200 square feet, with a minimum of 150 square feet, and no dependency on the primary residence’s size.

Attached ADUs are limited to 50% of the primary residence, capped at 1,200 square feet, though studios or one-bedroom units may go up to 850 square feet and two-bedroom units up to 1,000 square feet, with a 150-square-foot minimum.

JADUs cap at 500 square feet, starting from 150 square feet, created within the existing home.

Setbacks, Height, and Placement Requirements

Setbacks, height, and placement rules determine how you can position an ADU on your property while meeting safety and zoning standards.

You’ll see that side setbacks vary: newly constructed detached ADUs require a minimum 4-foot side setback, with zero side setbacks allowed for some small detached units, while exterior side yards on corner lots need 4 feet from easements or streets.

Rear setbacks also differ, with zero rear setbacks for certain small detached ADUs outside high fire zones and a mandatory 4-foot rear setback in Very High Fire Hazard zones.

Height rules matter too: under 16 feet you may enjoy reduced setbacks, but taller structures face stricter limits.

Placement requires a 6-foot separation from other structures, and front encroachment can be allowed under recent state and local rules for eligible sizes.

Setback regulations and height limitations guide every decision.

Required Permit Documents and Review Timeline

Maneuvering the required permit documents and the review timeline starts with knowing what you must submit and when. You’ll need detailed site plans and architectural drawings to prove zoning and building code compliance, plus documentation showing residential zoning and an existing primary dwelling.

Site plans must display setbacks, building separations, and lot coverage, while architectural plans specify square footage, height, and entrance locations for your ADU or JADU. Environmental notes may be required, such as septic plans or fire department approvals in wildfire-prone areas.

The permit review process aims to finalize approvals within 60 days of a complete application, with San Diego County usually taking 4–10 weeks. Incomplete submissions trigger corrections that pause the clock, and streamlined pathways may apply if standards are met.

When planning for an ADU, it's crucial to understand the benefits of incorporating sustainable features and working closely with professionals to enhance property value.

Additions, Ownership, and Special Programs for 2026 ADUs

ADUs in 2026 bring notable changes to ownership, occupancy, and special programs, making it easier for property owners to maximize usable space while meeting state and local requirements.

You’ll find that ADU ownership can’t be sold separately from the primary residence under standard rules, except in approved affordable housing programs or SB 9 lot splits, which must meet strict zoning and affordability criteria.

Owner-occupancy is no longer required for most ADUs, allowing you to rent both the main house and ADU if you choose.

JADUs retain occupancy rules, but new AB 1154 removes them for JADUs with separate bathrooms.

Multifamily sites gain flexibility with expanded detached ADU limits.

Special programs, including bonus and standard plan options, help streamline approvals and reduce costs.

Wrapping It Up

You’ll find that ADUs and additions in unincorporated San Diego County follow clear rules focused on safety and livability. By understanding eligibility, size limits, setbacks, and permit documents, you’ll streamline the process and avoid delays. The process emphasizes proper planning, timing, and coordination with county review steps. With careful preparation and attention to requirements, you can confidently pursue thoughtful upgrades that enhance value and housing options while staying compliant and informed throughout 2026.