ADU Rules in San Diego County, California
We track 7 cities in San Diego County. Each city writes its own ADU ordinance on top of California law, so size limits, fees, and design rules differ from one city to the next. Among the cities we track, Chula Vista has the lowest starting permit fees (About $3,951 in city fees for a standard-plan detached ADU; custom plans cost more).
Cities
7
Max Detached Size
1,200 sq ft
Build Costs From
$140,000
Pre-approved Plans
5 of 7 cities
San Diego County Cities Compared
| City | Max detached | Height | Permit fees | Build cost |
|---|---|---|---|---|
| San Diego | 1,200 sq ft | Up to two stories for detached ADUs on single-family lots, within the base and overlay zone height limit | $4,000 – $18,000 | $160,000 – $480,000 |
| Chula Vista | 1,200 sq ft | 16 ft detached (18 ft within 1/2 mile of transit, up to 20 ft to match the main home's roof pitch) | About $3,951 in city fees for a standard-plan detached ADU; custom plans cost more | $140,000 – $300,000 |
| Oceanside | 1,200 sq ft | 16 ft (detached) | $7,000 – $15,000 | $160,000 – $330,000 |
| Escondido | 1,200 sq ft | 16 ft (one story) | $7,000 – $14,000 | $155,000 – $320,000 |
| Carlsbad | 1,200 sq ft | 16 ft (detached) | $8,000 – $17,000 | $175,000 – $360,000 |
| El Cajon | 1,200 sq ft | 16 ft at a 4 ft setback (20 ft at 5 ft, 12 ft at 3 ft) | $6,500 – $13,000 | $150,000 – $305,000 |
| Vista | 1,200 sq ft | 16 ft | $6,500 – $13,000 | $150,000 – $305,000 |
San Diego ADU rules
San Diego's ADU Home Density Bonus Program lets owners add extra ADUs when some are deed-restricted affordable, but the City Council adopted 25 reforms that tighten it. Bonus and affordable ADUs now need sprinklers if detached, one parking space outside Transit Priority Areas, and a community enhancement fee, and ADUs in High or Very High Fire Hazard Severity Zones need 4 ft side and rear setbacks. Coastal Zone lots follow the new rules only after Coastal Commission certification.
Chula Vista ADU rules
Chula Vista offers 12 City Standard ADU Plans (about 500 to 1,200 sq ft, one to three bedrooms) that are reviewed in 14 business days instead of 21 and save about $1,000 in plan review fees. City fees for a detached standard-plan ADU were listed at about $3,951 before impact and school fees. A free parcel lookup tool shows what fits on your lot.
Oceanside ADU rules
Oceanside set up a Pre-Approved ADU Library for detached ADU plans under state law, but no vendor had submitted a plan as of mid-2026, so most homeowners still need a custom or prefab design. Even with a pre-approved plan, a site plan covering grading, drainage, setbacks and utilities is reviewed separately. Coastal bluff and hillside lots may need added geological or design review.
Escondido ADU rules
Escondido allows standard ADUs up to 1,200 sq ft, but units larger than 800 sq ft must meet the underlying zone's setbacks instead of the 4 ft state minimum. The city offers pre-approved detached ADU plans through its PAADU program, though a site-specific building permit is still required. Sloped hillside lots may also need a grading plan.
Carlsbad ADU rules
Properties in Carlsbad's Coastal Zone need a minor coastal development permit on top of the ADU permit, and local coastal program protections override the zoning code where they conflict. The city's Permit Ready ADU Program offers single-story detached plans at 400, 680, 800 and about 1,000 sq ft, though they were being updated to the 2025 building code. HOA review is common in master-planned neighborhoods.
El Cajon ADU rules
El Cajon offers standard pre-approved ADU plans, including an 800 sq ft two-bedroom and a 560 sq ft studio, delivered about 85% complete for site-specific finishing. The city also has an ADU loan program. Lots in east San Diego County suburbs are often larger than coastal lots, so full-size detached units are common.
Vista ADU rules
Vista offers four pre-approved ADU plans, from a 499 sq ft studio to a 1,149 sq ft three-bedroom, and waives plan check fees when you use one. Because of the city's hilly terrain, plans are not accepted until Land Development Engineering clears grading, and a soils report is usually required. Pre-approved plans are for single-family lots only.
Rules that apply in every California city are summarized in our California ADU law guide. See all California cities or compare every city side by side.