Town Permit Guide

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Can I build an ADU in Los Altos, California?

Los Altos, Santa Clara County · Ordinances checked 2026-10-05 · Reviewed · 14 cited sections

Allowed with a permit

Yes. Los Altos allows ADUs on single-family lots with ministerial approval within 60 days: one attached ADU, one detached ADU (up to 850 sq ft for one bedroom or 1,200 sq ft for two or more, 18 ft tall, 4-ft side and rear setbacks) and up to two junior ADUs of 500 sq ft inside the house. Owner occupancy is required only for a JADU.

ApprovalMinisterial (no hearing); decision within 60 days [1]
Units per single-family lot1 attached ADU + 1 detached ADU + 2 JADUs [2]
Detached ADU max size850 sq ft (1 bedroom) / 1,200 sq ft (2+ bedrooms) [3]
Attached ADU max sizeSame caps, and no more than 50% of the house; 850 sq ft always allowed [4]
JADU max size500 sq ft, inside the house [5]
Max heightDetached 18 ft; attached 16 ft or the zone height, whichever is greater [6]
Side and rear setbacks4 ft [7]
Owner occupancyRequired only for a JADU (deed restriction) [8]
Parking1 uncovered 9x18 space for a new ADU; none within 1/2 mile of transit [9]
Minimum rental term30 days [11]

Where and how many

ADUs are allowed on parcels zoned single-family, multifamily and mixed-use [12]. On a single-family lot you can have one attached ADU, one detached ADU and two junior ADUs (JADUs) [2]. Applications are approved ministerially, with no discretionary hearing, and must be decided within 60 days [1].

Size and placement

  • Detached ADU: up to 850 sq ft with one bedroom, or 1,200 sq ft with more than one; basements don't count [3].
  • Attached ADU: the same caps, and no more than 50% of the main house's floor area. An attached ADU of 850 sq ft or less can't be denied on that basis [4].
  • JADU: up to 500 sq ft, entirely inside the walls of the house, with an efficiency kitchen [5].
  • Height: 18 ft for a detached ADU; for an attached ADU, 16 ft or the zone's height limit, whichever is greater [6].
  • Setbacks: 4 ft from side and rear lines [7]. The front setback of the zone applies unless a site plan shows it physically precludes an ADU [14].

Owner occupancy and rentals

No owner-occupancy rule applies to ADUs. For a JADU, a deed restriction must be recorded requiring that an owner live in one of the units on the lot [8]. ADUs can't be rented for less than 30 days [11].

Parking and fees

A new ADU needs one uncovered 9 x 18 ft space, which can be in the front setback, in tandem or in the driveway [9]. No space is needed for conversions, garage replacements, or sites within a half-mile walk of a bus stop or train station [10]. City fees are proportional to unit size [13].

State law

California's ADU law sets minimum standards the city can't go below. State law now limits JADU owner-occupancy to units that share a bathroom with the house, so the city's blanket JADU owner-occupancy rule may be overridden by state law. State law also bars impact fees on ADUs of 750 sq ft or less. Starting January 1, 2027, state law (AB 956) will require cities to approve two new detached ADUs on a single-family lot by right; the city's code currently allows one.

See how Los Altos compares with 8+ other California towns on accessory dwelling units (adus) →

Next steps

  1. Pick a path: custom plans, a city pre-approved plan, or the city's free permit-ready detached ADU plans (see the Development Services ADU webpage).
  2. Check your lot's setbacks, utility connections and parking situation (transit within a half-mile walk removes the parking requirement).
  3. Submit a building permit application with the ADU submittal checklist to the Development Services Department (Planning and Building Divisions), 1 N San Antonio Road.
  4. For a JADU, record the owner-occupancy/no-separate-sale deed restriction with the Santa Clara County Recorder before the permit is issued.

Common questions

Are ADUs allowed in Los Altos, California?
Yes. Los Altos allows ADUs on single-family lots with ministerial approval within 60 days: one attached ADU, one detached ADU and up to two junior ADUs of 500 sq ft inside the house.
How big can a detached ADU be in Los Altos, California?
A detached ADU can be up to 850 sq ft for one bedroom or 1,200 sq ft for two or more bedrooms. It can be 18 ft tall with 4-ft side and rear setbacks.
Do I have to live on the property to build an ADU in Los Altos, California?
No. Owner occupancy is required only for a junior ADU.
Can I rent my ADU short term in Los Altos, California?
No. ADUs can't be rented for less than 30 days; the minimum rental term is 30 days.

California's statewide ADU law

California's ADU law (Gov. Code §§66310–66342, recodified from §65852.2; latest amendments effective January 1, 2026) overrides conflicting city rules, including in charter cities. Cities must approve ADUs ministerially (no hearing) within 60 days of a complete application, or the permit is deemed approved.

What cities cannot require or do:

  • Owner-occupancy for an ADU.
  • A minimum lot size.
  • Side or rear setbacks over 4 feet for a new ADU, or any setback for a converted existing structure.
  • Size, lot coverage or floor-area rules that block an ADU of at least 800 sq ft. Size caps can't be under 850 sq ft (1,000 for 2+ bedrooms).
  • Parking within half a mile walking distance of public transit, or replacement parking for a garage converted to an ADU.
  • Impact fees on ADUs of 750 sq ft or less.

By right on a single-family lot: one converted ADU plus one junior ADU (JADU, up to 500 sq ft inside the house), plus one new detached ADU (up to 800 sq ft, 16 ft tall). Owner-occupancy may be required only for a JADU that shares a bathroom.

Short-term rentals: cities may bar ADU rentals under 30 days, and must for by-right ADUs, JADUs and SB 9 units.

Coming January 1, 2027: AB 956 raises the by-right count to two new detached ADUs per single-family lot.

SB 9 (§§65852.21, 66411.7) allows two homes on a single-family lot, or a split into two lots of at least 1,200 sq ft (with a 3-year owner-occupancy affidavit).

State sources: Gov. Code §66314 (ADU ordinance standards) · Gov. Code §66315 (no owner-occupancy requirement) · Gov. Code §66317 (ministerial review, 60-day deadline) · Gov. Code §66321 (size, setback and height limits on local rules) · Gov. Code §66322 (parking exemptions) · Gov. Code §66323 (by-right ADUs and JADUs) · Gov. Code §66333 (junior ADUs) · Gov. Code §66311.5 (impact fees) · AB 956 (2026), Stats. 2026, ch. 791 · Gov. Code §65852.21 (SB 9 two-unit projects) · Gov. Code §66411.7 (SB 9 urban lot splits) · HCD, Accessory Dwelling Units (ADU Handbook, updated March 2026)

What the ordinance says

Exact text from Los Altos's published ordinances. Section numbers are as printed in the source.

  1. Sec. 14.14.030 Review procedures, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    An application for an accessory dwelling unit or a junior accessory dwelling unit shall be considered and approved ministerially without discretionary review, processes, or provisions. The review of any accessory dwelling application shall be approved or denied in sixty (60) days or less.
  2. Sec. 14.14.050(A) Maximum number of units, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    One attached accessory dwelling unit and one detached accessory dwelling unit and two junior accessory dwelling units per lot with a proposed or existing single-family dwelling.
  3. Sec. 14.14.070 Square footage allowance (detached), Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    A detached single-family residential ADU shall not exceed eight hundred fifty (850) square feet in floor area for one bedroom unit, or one thousand two hundred (1,200) square feet with more than one bedroom.
  4. Sec. 14.14.070 Square footage allowance (attached), Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    The total floor area for an attached ADU shall exclude any basement area and shall not be more than fifty (50) percent of the floor area of the existing or proposed principal residence. Notwithstanding this fifty (50) percent threshold requirement, an attached ADU of eight hundred fifty (850) square feet or smaller cannot be denied.
  5. Sec. 14.14.020 Definitions, "Junior accessory dwelling unit", Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    "Junior accessory dwelling unit" (or "junior ADU" or "JADU") means a unit that is no more than five hundred (500) square feet in size, includes an efficiency kitchen consistent with building code standards, is contained entirely within the walls of a single-family residence and may include separate sanitation facilities or may share sanitation facilities with the existing structure or unit.
  6. Sec. 14.14.060 Development standards (table, height row), Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    Maximum height NA The greater of 16 feet or the height of the underlying zoning district whichever is greater. 18 feet
  7. Sec. 14.14.060 Development standards (table, side/rear setback rows), Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    Minimum side setback NA 4 feet 4 feet Minimum rear setback NA 4 feet 4 feet
  8. Sec. 14.14.090(M) Deed Restriction, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    The deed restriction shall prohibit the sale of the junior accessory dwelling unit separate from the sale of the single-family dwelling, and one of the dwellings on the lot must be occupied by at least one legal owner of the property, unless the property is owned by a governmental agency, land trust or housing organization.
  9. Sec. 14.14.100 Parking requirements, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    One uncovered parking space of nine feet by eighteen feet (9 X 18) shall be required for a newly constructed single-family residential accessory dwelling, which may be located within the front setback, in tandem and in an existing driveway including within an interior side yard setback area, unless the development services director determines such parking is not feasible due to specific site, topographical constraints or fire and life safety.
  10. Sec. 14.14.100(3) Parking exemptions, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    The single-family residential accessory dwelling is within one-half mile walking distance of a public transit station, such as a bus stop or train station.
  11. Sec. 14.14.090(A) Short-Term Rental, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    An ADU shall not be rented for periods less than thirty (30) days.
  12. Sec. 14.14.040(A) Location permitted, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    ADUs may be permitted in the following zones: on parcels zoned for single-family, multi- family and mixed-use.
  13. Sec. 14.14.090(D) Impact Fees, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    Any applicable fees established by the City of Los Altos shall be proportional based on unit size.
  14. Sec. 14.14.060 footnote 1, Municipal Code Chapter 14.14 - Accessory Dwelling Units, p. 1
    Any proposed accessory dwelling shall conform to the front setback of the underlying zone unless it is demonstrated through a site plan that a physical preclusion exists and hinders the development of an accessory dwelling as allowed by this code.
This page summarizes Los Altos's posted ordinances as of 2026-10-05. Ordinances are amended, and individual lots can have overlays, subdivision covenants, or HOA rules that are stricter. Confirm with Development Services Department - Code Enforcement Division (Building Division 650-947-2752), 1 N San Antonio Road (650-947-2775) before you build. Spot an error?