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Building an ADU in Los Altos, CA

Checked against the city's ADU pages on Oct 18, 2026.

Can I build one?
Yes, up to 1,200 sq ft A detached ADU can be 1,200 sq ft with 2+ bedrooms. The city charges $0 for the ADU building permit and plan check.[1][2]
What will the city charge?
$0 $0 for the city ADU building permit, trade permits and plan check. See every fee[2]
Who builds here?
11 licensed builders Each lists Los Altos on its own site and holds an active CSLB license. See the list
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Licensed ADU builders in Los Altos

Ranked by a public score anyone can check: license, years licensed, ADU types and cities shown on their own sites, a local office, and published prices. Nobody pays to move up. Quote requests go to our team with the builder you picked. How we rank

What Los Altos allows

  • Detached ADU, max size[1]

    850 sq ft with 1 bedroom; 1,200 sq ft with more than 1. Basements don't count

  • Attached ADU, max size[1]

    Same sizes, and no more than 50% of the house. An attached ADU of 850 sq ft or less can't be denied under the 50% rule

  • Junior ADU (inside the house)[1]

    Up to 500 sq ft. You can add up to 150 sq ft for the entry, counted in the 500

  • Height[1]

    Detached: 18 ft. Attached: 16 ft or the zone height, whichever is greater

  • Side and rear setbacks[1]

    4 ft side and rear; front setback follows the zone; 5 ft from other buildings

  • Floor area and lot coverage[1]

    ADUs don't count toward FAR or lot coverage

  • Units on a single-family lot[1]

    1 attached ADU + 1 detached ADU + 2 JADUs, as the city code is written

  • Parking[1]

    1 uncovered 9 x 18 ft space for a new ADU; it can be tandem, in the driveway or in the front setback. None for conversions, garage replacements, within 1/2 mile of transit, in a historic district, or with car share within a block

  • Owner must live on site[1][3]

    No for an ADU. City code requires it for a JADU; since 2026 state law requires it only when the JADU shares a bathroom
  • The city code allows 2 JADUs per lot, but state law allows one JADU per lot. Ask Planning before you plan a second one.[1][3]
  • Each ADU needs its own side-hinged entrance and its own bathroom.[1]
  • The city sends a voluntary rental income survey each year. Answering is optional.[1]
ADU rules in Los Altos drawn on a typical lot Detached ADU, city standards: up to 1,200 square feet, 4 feet from side and rear lot lines, 18 feet tall. Parking: 1 uncovered space, with exemptions. Rear lot line Street Main house ADU up to 1,200 sq ft 18 ft tall 4 ft 4 ft 5 ft apart Parking: 1 uncovered space, with exemptions
Detached ADU, city standards. Not to scale.

City fees for an ADU in Los Altos

Fee lines for an ADU in Los Altos
ADU building permit, trade permits and plan check $0[2] The FY 2026-27 schedule lists the ADU building permit, ADU electrical, mechanical or plumbing permit, and ADU plan check at $0.00.
Construction tax $0.42 per sq ft (single family)[2] The schedule does not say whether ADUs pay it.
Impact fees $0 under 750 sq ft; above that, proportional to unit size[3][1] We found no city park or impact fee amounts for ADUs.
School fees Los Altos SD $3.58 per sq ft; MVLA high school $1.72 per sq ft[4][5][3] Only for ADUs over 500 sq ft. MVLA rises to $1.79 on Nov 13, 2026.
Water and sewer connection Not charged as a new residential use (city code)[1][2] The ADU can share the main home's service or have its own meters. The fee schedule lists a $759.16 city sewer permit and a $152.04 tap-in; ask Public Works which apply.
School fee rates for districts in Los Altos (2)

You pay Los Altos School District (elementary) and MVLA (high school). We did not check whether any parcels fall in other districts.[4][5]

  • Los Altos School District[4][6] $3.58/sq ft
  • Mountain View-Los Altos Union High School District[5] $1.72/sq ft
Total cost in Los Altos, fees plus building

How the permit works

  1. 1

    Learn the rules

    Read the ADU Information Guide and city code. A planner answers questions at 650-947-2750.[7][8]

  2. 2

    Pick a plan

    Use a custom design, buy a pre-approved plan from a designer, or use the city's free permit-ready plans.[7][8]

  3. 3

    Email your submittal

    Send the items on the ADU Submittal Requirements list to the Building Division by email. Review is ministerial: no planning permit or hearing.[8]

  4. 4

    Answer comments and get the permit

    Resubmit if reviewers ask for changes. Once all departments approve, the city issues the building permit.[7]

  5. 5

    Build and pass inspections

    Schedule inspections from the Building Division webpage. After the final inspection the ADU can be occupied.[7]

State deadline: City code says the city approves or denies an ADU application within 60 days.[1]

Preapproved plans

The city gives away permit-ready plans for detached ADUs in three sizes and three styles (Mediterranean, Traditional, Contemporary). Private designers also sell plans the city has pre-reviewed.[8][7]

  • City Permit-Ready plans (free) Studio/1 bed 525 sq ft; 1 bed 854 sq ft; 2 bed 1,190 sq ft
  • Wellmade Fillmore 330 sq ft; Ashbury 434 sq ft
  • ADORE Homes HUD unit, 800 sq ft

City plans are free but can't be changed beyond the built-in options; full sets can be viewed at City Hall. Private plans are bought from the designer. The city publishes no prices for them.

Common questions

How big can an ADU be in Los Altos?

A detached ADU can be 850 sq ft with 1 bedroom or 1,200 sq ft with more. An attached ADU has the same limits and can't exceed 50% of the house. A junior ADU is up to 500 sq ft.[1]

Do I need parking for an ADU in Los Altos?

A new ADU needs 1 uncovered space, which can be tandem or in the driveway. You don't need one for a conversion, a garage replacement, or within 1/2 mile of transit.[1]

How much does an ADU permit cost in Los Altos?

The FY 2026-27 fee schedule lists the ADU building permit, trade permits and plan check at $0. School fees still apply over 500 sq ft: $3.58 per sq ft for Los Altos SD and $1.72 for MVLA.[2][4][5]

Does Los Altos have free ADU plans?

Yes. The city offers free permit-ready plans for detached ADUs of 525, 854 and 1,190 sq ft, each in three styles.[8]

How tall can an ADU be in Los Altos?

18 ft for a detached ADU. An attached ADU can be 16 ft or the zone height, whichever is greater.[1]

Nearby cities

What we couldn't confirm

  • No city park or impact fee amounts for ADUs found.
  • Whether the $0.42 per sq ft construction tax applies to ADUs is not stated.
  • Water provider connection costs not confirmed.
  • No typical permit timeline published.
  • Parts of Los Altos that may be in other school districts were not checked.

Sources

Every fact on this page links to one of these. We read each one on the date shown.

  1. 1. City of Los Altos (Municode, official code host) LAMC Ch Checked Oct 18, 2026
  2. 2. City of Los Altos FY2026-27 fee schedule (effective July 1, 2026): ADU Building Permit $0.00 Checked Oct 18, 2026
  3. 3. California Department of Housing and Community Development (HCD) All state ADU/JADU rules used in state_baseline.md (sizes, heights, setbacks, parking, owner-occupancy, JADU, Checked Oct 18, 2026
  4. 4. Los Altos School District $3.58/sf residential Checked Oct 18, 2026
  5. 5. Mountain View-Los Altos Union HSD MVLA share $1.72/sf Checked Oct 18, 2026
  6. 6. Los Altos School District Adopted Dec 15, 2025 Checked Oct 18, 2026
  7. 7. City of Los Altos ADU Information Guide: detached up to 1,200 sq ft, 18 ft Checked Oct 18, 2026
  8. 8. City of Los Altos Ministerial review (building permit only) Checked Oct 18, 2026