Can I Build an ADU in Aliso Viejo?

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

Statewide default cap for detached new-construction ADUs in the absence of a compliant local ADU ordinance. The unconditional by-right floor a city must always allow is 800 sq ft (see Guaranteed minimum size); a city with a compliant ordinance may set its own ceiling.

Attached ADU height capped at 25 ft / 2 stories (or the underlying zone limit, whichever is lower); size per state floor

Aliso Viejo specifies that an attached ADU may not exceed 25 ft or the primary dwelling's zone height, whichever is lower, and may not exceed two stories. Detached/converted ADUs are limited to one story (§ 15.14.080(I)(8)). State minimum-size protections (≥850/1,000 SF) still apply.

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

Detached ADU 16 ft; up to 18 ft within ½ mi of a major transit stop / high-quality transit corridor, plus 2 more ft (to 20 ft) to align roof pitch with the primary dwelling; 18 ft on a lot with an existing/proposed multistory multifamily dwelling. An ATTACHED ADU may reach 25 ft (or the underlying zone limit, whichever is lower) but no more than two stories. Height measured per the California Building Code.

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 for ADUs (the prior ADU owner-occupancy provision in Ord. 2023-235 was removed after HCD review). A JADU is generally subject to owner-occupancy — the owner must reside in the primary dwelling or the JADU — with stated exceptions; a JADU deed restriction is recorded before its certificate of occupancy (§ 15.14.080(H)(8)).

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

Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.