ADU Regulations in Contra Costa County, California (2026)
Summary from local ordinance data. Verify with city planning for your specific lot.
Regulations at a glance
| Rule | Value |
|---|---|
| Max ADU Size | 800 sq ft |
| Side Setback | 4 ft |
| Rear Setback | 4 ft |
| Max Height | 16 ft |
| Approval Type | Ministerial (by-right) per Gov Code §65852.2 |
| Parking Requirements | Often waived per state law; check local ordinance |
Local rules & notes
Source Document Type: The provided text is an academic research paper ('Where Will Accessory Dwelling Units Sprout Up...') rather than a municipal code. Rules extracted reflect state-wide mandates discussed in the text. HOA Restriction Override: State law explicitly voids HOA restrictions that prohibit ADUs or their rental, a significant value-add for properties in planned developments.
For the official ordinance and latest updates, check your city or county planning department.
Frequently asked questions about ADU regulations in Contra Costa County
What is the maximum ADU size in Contra Costa County, California?
In Contra Costa County, the maximum ADU size is typically 800 square feet, depending on whether the unit is attached or detached. California state law allows up to 1,200 sq ft for detached ADUs and 800 sq ft for attached in many jurisdictions; Contra Costa County may follow state defaults or have local limits. Verify with Contra Costa County planning for your specific lot.
What are the setback requirements for ADUs in Contra Costa County?
In Contra Costa County, typical setback requirements are 4 feet from the side property line and 4 feet from the rear. These may be reduced to 4 feet under California Government Code § 65852.2 where applicable. Check with Contra Costa County planning for overlay zones or design standards that could affect your site.
What is the maximum height for an ADU in Contra Costa County?
In Contra Costa County, the maximum height for an ADU is generally 16 feet. State law often allows up to 16 feet for detached ADUs and up to 25 feet when within 4 feet of the property line in some cases. Confirm with Contra Costa County or county planning for your zone.
Is ADU approval ministerial in Contra Costa County?
In Contra Costa County, ADU approval is typically Ministerial (by-right) per Gov Code §65852.2. Ministerial (by-right) review means the city must approve qualifying applications without discretionary review, per California Gov Code § 65852.2. Your project must still meet objective standards; Contra Costa County planning can confirm the exact process.
Are there parking requirements for ADUs in Contra Costa County?
In Contra Costa County, parking for ADUs is generally Often waived per state law; check local ordinance. California law often waives parking for ADUs within a half-mile of transit or in certain historic districts. Check with Contra Costa County planning for your address.
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