Building an ADU in San Diego: A Homeowner’s Complete Guide
Sizes, setbacks, permits, costs and timelines — what San Diego homeowners should know before adding an accessory dwelling unit.
Why ADUs make sense in San Diego
San Diego’s housing costs and multigenerational households have made accessory dwelling units one of the most practical home improvements in the region. An ADU can house aging parents or adult children, create long-term rental income, or give you a smaller place to live while renting the main house.
California has spent the last several years making ADUs easier to build, and San Diego jurisdictions have followed. But “easier” doesn’t mean simple — the right ADU depends on your lot, your utilities and your goals.
The four types of ADUs
- Detached ADU — a standalone unit, typically in the backyard. Most privacy, most design freedom.
- Attached ADU — built as an addition with its own entrance. Often more efficient to connect to existing utilities.
- Conversion ADU — an existing garage, accessory structure or part of the home converted to a unit. Usually the fastest and least expensive.
- Junior ADU (JADU) — up to 500 square feet within the existing home, with at least an efficiency kitchen and its own exterior entrance.
How big can an ADU be?
State law sets the framework. In general:
| Type | General size limit |
|---|---|
| Detached ADU | Up to 1,200 sq ft |
| Attached ADU | Up to 50% of the main home or 1,200 sq ft (local rules vary) |
| Junior ADU | Up to 500 sq ft within the home |
State law also generally allows ADUs with 4-foot side and rear setbacks, and protects the ability to build at least an 800-square-foot ADU in many situations even where other local standards would limit it. Height limits depend on the ADU type and location — commonly 16 feet for a single-story detached unit, with more allowed in some cases.
Permits: who reviews your ADU?
That depends on where your property is:
- City of San Diego — Development Services Department (DSD).
- Unincorporated county (e.g. Ramona, Alpine, Fallbrook, Valley Center) — County of San Diego Planning & Development Services.
- Other cities — Chula Vista, Carlsbad, Encinitas, Oceanside, La Mesa, El Cajon, Escondido and others each run their own building departments.
Under state law, a local agency must act on a complete ADU application within 60 days. Plan-check comments and resubmittals can add time, which is why a well-prepared first submittal matters.
What drives ADU cost
Every lot is different, so we price ADUs individually. The biggest variables are:
- Utilities — distance to sewer and water connections, and whether your electrical service needs an upgrade (very common).
- Site conditions — slope, soil, access for equipment, and any retaining walls.
- Size and type — conversions usually cost less than new detached units.
- Finishes — cabinets, counters, flooring and fixtures.
- Fees — state law exempts ADUs under 750 sq ft from impact fees and limits them on larger ADUs, but plan-check, permit and utility connection fees still apply.
Rentals, parking and owner occupancy
A few rules homeowners often ask about:
- Parking — in many cases no additional parking is required, including within a half-mile walk of public transit or when a garage is converted.
- Owner occupancy — current state law does not require owner occupancy for ADUs; JADUs have separate owner-occupancy rules.
- Short-term rentals — many jurisdictions, including the City of San Diego, restrict renting ADUs for short stays. Plan around long-term rental unless you’ve confirmed otherwise.
A realistic timeline
Typical phases for a detached ADU:
- Feasibility — lot review, utility check and size options.
- Design — layout, exterior, and selections.
- Permitting — submittal, plan check and corrections.
- Construction — foundation through finishes and final inspection.
Garage conversions and JADUs typically move faster than new detached units. We provide a schedule specific to your project during feasibility.
The best ADU projects start with the lot, not the floor plan.
This article is general information for San Diego-area homeowners, not legal or permitting advice. Codes and local rules change; confirm requirements for your property with the responsible agency or a qualified professional.
