Can I Build an ADU in Mountain View?

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).

1,000 sq ft

Mountain View caps a detached ADU at 850 sq ft (studio/1-bedroom) or 1,000 sq ft (2+ bedrooms) — below the 1,200 sq ft state default. At least 800 sq ft must still be allowed via the state-mandated path.

50% of the existing primary unit's gross floor area, but not less than 850 sq ft (1 bedroom) or 1,000 sq ft (2+ bedrooms)

Matches the state attached formula but Mountain View codifies the 850/1,000 sq ft floors and the 50%-of-primary cap explicitly.

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

28 ft

Mountain View sets a 28-ft local cap (including a basement level) for a 1- or 2-story ADU — more permissive than the 16/18-ft state baseline, which still binds where state law guarantees it.

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 underlying zone's front setback requirement

Mountain View applies the base-zone front setback to ADUs; the state-mandated 800 sq ft / 4-ft-setback ADU cannot be wholly precluded.

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. A JADU requires an owner to occupy the primary dwelling or the JADU, unless the property is owned by a government agency, land trust, or housing organization — a carve-out Mountain View spells out by deed restriction.

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.