A San Diego ADU can run as small as 150 square feet or as large as 1,200, and — this surprises most homeowners — the side and rear setback can go all the way to the property line in many cases, not the 4 feet people assume from generic California ADU articles. Parking is often not required at all. The specifics depend on your exact property, but the baseline rules are worth knowing before you sketch a single wall.
The state law changed its own address in 2026
California’s ADU law used to live entirely under Government Code Section 65852.2. As of the 2024 reorganization, it’s spread across Government Code Sections 66310–66342 — if you’re reading an older article that only cites 65852.2, treat its specifics as potentially outdated. A newer change worth knowing: SB 543, effective January 1, 2026, redefined what counts toward an ADU’s size. The law now measures “livable space” (a defined term covering living, sleeping, eating, cooking, and sanitation areas) instead of the older “living area” language — a distinction that can matter when a plan set is right at a size limit.
State law sets a floor cities can’t fall below: any city must allow at least an 800 sq ft detached ADU with no more than a 4-foot side/rear setback, regardless of what its local code otherwise requires. Cities are free to be more generous than that floor — and in San Diego’s case, the city’s own rule is more generous.
San Diego’s actual setback rule
The City of San Diego’s Information Bulletin 400 allows an ADU to encroach into the side and rear setback areas of its zone, up to the property line itself — not just the state’s 4-foot minimum. There are two situations where the standard 4-foot setback still applies:
- ✓The ADU is taller than 16 feet and sits next to a residentially zoned property
- ✓The property is in a fire hazard zone, regardless of the ADU’s height
Front-yard setbacks follow the standard rule for whatever zone the property sits in — there’s no ADU-specific relief there.
Size limits, in one table
| Minimum | Maximum | |
|---|---|---|
| ADU (attached or detached) | 150 sq ft | 1,200 sq ft |
| JADU (junior ADU) | 150 sq ft | 500 sq ft |
One exception worth knowing: converting an existing accessory structure (like a garage) or part of the existing primary home into an ADU is not subject to the 1,200 sq ft maximum — that cap applies to new construction, not conversions.
ADUs at 800 sq ft or smaller also get favorable treatment on floor-area-ratio (FAR) and lot-coverage rules in several scenarios — including cases where the underlying lot is already over its FAR limit. A JADU’s floor area isn’t counted toward the property’s total gross floor area at all.
Parking: often not required
San Diego doesn’t require additional off-street parking for an ADU within half a mile of public transit — a real exemption that applies to a meaningful share of city lots. Other common exemptions include ADUs under 500 sq ft and ADUs created from existing space within the primary home. If your property sits in the Beach Impact Area of the Coastal Overlay Zone, the exemptions narrow — a detached ADU there may need one parking space unless it qualifies under transit proximity, size, or another specific exemption.
None of these should be assumed without checking your specific address — a lot that looks similar to a neighbor’s can fall on a different side of the transit-distance line.
Why this matters before the floor plan is drawn
Setback and parking rules shape where an ADU can physically sit on a lot — which affects the entrance, privacy from the main home, and how much of the yard is left afterward. Confirming these specifics during feasibility, before a design is finalized, avoids redesigning around a setback or parking requirement discovered mid-project. This is the same reason we build feasibility into the start of every ADU project rather than treating it as a formality.
Schedule a consultation and we’ll check these specifics against your actual property before any design work begins.
Frequently asked questions
Related reading
- ✓How Much Does an ADU Cost in San Diego?
- ✓San Diego ADU Permit Process: What Homeowners Should Expect
- ✓ADU Builders in San Diego (service page)
- ✓ADU Financing in San Diego
