Can I Build an ADU in Sunnyvale?

Yes — by right

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

1 conversion ADU + 1 new-construction ADU + 1 JADU (3 units in addition to the main house)

Explicitly allows one conversion ADU, one new-construction ADU, and one JADU, in any order — three accessory units plus the main single-family dwelling.

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).

1,000 sq ft

Detached ADU capped at 1,000 sq ft gross floor area (below the 1,200 sq ft state default), with no restriction on the number of bedrooms. The 800 sq ft state ADU is allowed by right regardless.

Up to 1,000 sq ft gross floor area (no separate percentage-of-primary cap stated)

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

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

5 ft

5 ft of separation between a detached ADU and the primary dwelling applies only to non-streamlined detached ADUs; streamlined ADUs (≤800 sq ft, etc.) have no separation requirement, and state law sets none.

None

Sunnyvale requires no off-street parking for any ADU regardless of transit proximity, and no replacement parking for garage conversions.

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

A streamlined ADU (≤800 sq ft, 4-ft setbacks, height-compliant) needs only a ministerial building permit; a non-streamlined ADU (>800 sq ft) also requires a still-ministerial Miscellaneous Plan Permit. No discretionary review for any ADU.