Can I Build an ADU in Concord?

Yes — by right

ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.

1 ADU + 1 JADU

At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).

Conversion ADUs (≥1, up to 25% of units) + up to 8 detached

Conversions of non-livable space (at least 1, or up to 25% of existing units) plus up to 8 detached ADUs on a lot with existing multifamily — never exceeding the number of existing units. JADUs are single-family only.

Allowed

Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).

1,200 sq ft

Lot-size tiered: 1,000 sq ft on lots under 12,000 sq ft, 1,200 sq ft on lots of 12,000 sq ft or more (excluding up to 230 sq ft for an attached garage/carport). An 800 sq ft ADU with 4-ft side/rear setbacks must always be allowed regardless of the cap.

Lesser of 50% of the principal dwelling's floor area or 1,000 sq ft (lots < 12,000 sq ft) / 1,200 sq ft (lots ≥ 12,000 sq ft), excluding up to 230 sq ft for an attached garage/carport; an 800 sq ft ADU is always allowed

800 sq ft

An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).

500 sq ft

16 ft

16 ft baseline; cities must allow 18 ft within ½ mi of a major transit stop or where the primary dwelling is two-story, and 20 ft on a lot with a multistory multifamily building.

4 ft

A city cannot require more than 4 ft side or rear setback; conversions of existing structures are exempt.

4 ft

Must comply with the principal dwelling's front setback; where the principal dwelling encroaches into the front setback, the ADU may encroach to the same extent

More specific than the state default — Concord ties the ADU front setback to the principal dwelling rather than leaving it 'per base zone.' The state guarantee of an 800 sq ft / 16-ft / 4-ft-setback ADU still controls.

None required

No statewide separation requirement between the ADU and the primary dwelling.

Up to 1 space

At most 1 space per ADU (or per bedroom, whichever is less) — and waived in the common cases below.

Yes — no parking required near transit & for conversions

No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.

Not required

When a garage/carport is demolished or converted to build an ADU, replacement parking cannot be required.

Ministerial (by right)

No public hearing or discretionary design review for a qualifying ADU.

60 days

The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.

Only for a JADU

CDC § 18.200.180(C)(15) requires owner-occupancy of one unit on the lot for ADU building-permit applications received after 2024-12-31, but current state law (Gov. Code § 66315) bars owner-occupancy requirements for ADUs, so the requirement is enforceable for JADUs only (CDC § 18.200.180(E)(4)). Verify how Concord is currently applying this before relying on it.

Waived under 750 sq ft

An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.

Building permit

Ministerial building permit only (no discretionary review). Concord additionally requires the ADU to be built on a permanent foundation.