Can I Build an ADU in Danville?

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 (or up to 3 added units: 1 interior ADU + 1 JADU + 1 detached ADU ≤ 800 sq ft)

Two added units = one attached or detached ADU + one JADU. Three added units = one interior ADU (within or converted from the home) + one JADU + one detached ADU not exceeding 800 sq ft.

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

1,200 sq ft maximum for a detached ADU in residential districts with a minimum lot size under 40,000 sq ft. On lots in a district requiring a 40,000 sq ft minimum lot size or larger (Danville's large hillside/estate lots), the maximum rises to 2,000 sq ft. 800 sq ft is the protected by-right floor, not Danville's detached cap.

1,200 sq ft and ≤ 50% of the primary dwelling, but a 850 sq ft (or 1,000 sq ft if 2+ bedrooms) ADU is always allowed; 2,000 sq ft on ≥ 40,000 sq ft-minimum lots

Attached ADU is capped at 1,200 sq ft and 50% of the existing/proposed primary residence, with the state-protected 850/1,000 sq ft minimum always guaranteed. On lots zoned for a 40,000 sq ft minimum, the cap is 2,000 sq ft (still ≤ 50% of the primary).

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 for a detached ADU; 18 ft (+ 2 ft for roof pitch matching the primary dwelling, so 20 ft max) within ½ mi of a major transit stop or high-quality transit corridor; up to 24 ft if the ADU meets the primary dwelling's setbacks. Attached ADUs may reach 25 ft, or the primary dwelling's height limit if primary-residence setbacks are met.

4 ft

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

4 ft

No front setback may block the mandatory 800 sq ft / 16-ft / 4-ft-setback ADU; otherwise per base zone

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

No owner-occupancy requirement for ADUs (the prior sunset was removed). A JADU may require owner-occupancy, principally where it shares sanitation with the main house.

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 review)

Ministerial review for ADUs consistent with the chapter's objective standards; an ADU/JADU that does NOT meet the objective design/development standards is routed to an Administrative (noticed) review instead. ADUs of 800 sq ft or less are exempt from local development standards beyond Gov. Code § 66323 (§ 32-76.13). The chapter also imposes an objective exterior-design-compatibility standard (matching paint colors, siding, and roof materials).