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What an ADU costs in Los Gatos

Two numbers, kept apart. City fees come from the city's own fee pages. The build price is our estimate from the last owner survey and today's published prices. How we got it

Official City fees

Line by line

The city doesn't publish a total for an ADU, so we list each charge.See every fee [1]

Our estimate Building it

$350k–465k

750 sq ft detached, design and construction. Middle of the range: $405k.[2][3][4][5]

All in, before school and utility fees: about $350k to $465k for a 750 sq ft detached ADU. Adjust it for your lot

12 licensed builders list Los Gatos on their own sites. Your quote request goes to the Bay Area ADU Builders team.

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Estimate your ADU

Change the type and size. City fees come from Los Gatos's own averages; the building cost is our estimate.

Type
School districts
Building it (our estimate)
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City permit fees (city average)
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School fees (rate × the whole ADU once it's over 500 sq ft, capped at $5.38)
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Likely total
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Building (middle) City fees School fees

Not included: water and sewer connection, and site surprises like a long utility run or a crane. See the fee list below.

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Licensed builders who list Los Gatos

All 12

The top three by our public score for Los Gatos. Some publish prices, which is the quickest check on the estimate above.

Every fee Los Gatos can charge

Building permit, by valuation $1,749 for the first $100,000, plus $9.84 per $1,000 up to $500,000[1] Valuation is the ICC table × 2.32 (× 3.246 on hillside lots). FY 2026-27 schedule, effective July 1, 2026.
Plan review and surcharges Plan review 65% and Title 24 surcharge 15% of the building fee; $68 issuance; electrical, mechanical and plumbing $0.12 per sq ft each[1]
Planning add-ons Planning plan check 20% of the building fee; General Plan surcharge 0.5% of valuation; 4% permit tracking[6]
Traffic impact fee $0 under 750 sq ft; $1,128 per daily trip at 750 sq ft and up, scaled to the main home[7][1] The Town does not publish the trip rate it uses for an ADU.
Construction taxes $0.18 capital improvement + $0.18 underground utility + $0.04 park fund, per sq ft of added floor area[1] The schedule doesn't say whether these apply to a detached ADU.
School fees Los Gatos Union SD $4.07 + Los Gatos-Saratoga Union HSD $1.66 per sq ft[8][9][10] LGUSD charges nothing on remodels under 500 sq ft. Campbell Union HSD ($1.61) also lists Los Gatos. Check which districts serve your parcel.
Sewer connection (West Valley Sanitation District) $6,727 max connection + $1,024 max treatment plant capacity[11] Smaller ADUs pay $511.16 and $73.53 per drainage fixture unit. The district's fee tables are labeled FY2018/19 to FY2020/21.
Water (San Jose Water) No published ADU fee[12] San Jose Water quotes new service installation costs case by case.

How we estimate the building cost

The last survey of what Bay Area owners actually paid is from UC Berkeley in 2021: a median of $329 per sq ft for ADUs permitted in 2018 and 2019.[2] Construction prices in California have risen about 60% since then by the state's own cost index (2018-2019 average 6,719 to September 2026: 10,717).[3] We check that against two current numbers and use the spread as the range.

  • UC Berkeley 2021 owner survey, Bay Area median for ADUs built 2018-19 ($329 per sq ft), raised by the California Construction Cost Index (x1.595)[2][3] $525/sq ft
  • San Mateo County ADU Resource Center rule of thumb for design, construction and fees[4] $450 to 600/sq ft
  • Abodu published all-in price, 800 sq ft 2 bed / 2 bath ($424,800)[5] $531/sq ft

Other ADU types

  • Attached ADU: Detached band scaled by the survey's addition-to-detached ratio ($250 vs $300 per sq ft statewide)[2] $375 to 500/sq ft
  • Garage conversion: UC Berkeley 2021 owner survey, statewide median for garage ADUs ($189 per sq ft), raised by the California Construction Cost Index[2][3] $302/sq ft
  • Garage conversion: Same, with the survey's Bay Area premium over the statewide median (x1.32)[2][3] $397/sq ft
  • Garage conversion: SYMBiHOM published garage conversion price, $150K to $225K (per sq ft at a 400 sq ft two-car garage)[13] $375 to 560/sq ft
  • Junior ADU: UC Berkeley 2021 owner survey, statewide median for converting part of the main home ($173 per sq ft), raised by the California Construction Cost Index[2][3] $276/sq ft
  • Junior ADU: Same, with the survey's Bay Area premium (x1.32)[2][3] $363/sq ft

Smaller units cost more per foot. We scale by size the way Abodu's own price list does. The survey counted design and permits in its figure, so a little of the city fee may overlap.

Prefab prices you can check

Abodu published all-in prices (home + typical installation).[5]

  • Studio, 385 sq ft$298,800
  • 1 bed, 500 sq ft$324,800
  • 2 bed / 1 bath, 625 sq ft$358,800
  • 2 bed / 2 bath, 800 sq ft$424,800
  • 3 bed / 2 bath, 1,070 sq ft$464,800
  • 3 bed / 3 bath, 1,195 sq ft$498,800

Not included: Survey package ($6,000), trenching past 50 ft, crane past 100 ft, demolition, site engineering and sales tax.

What other sites say

  • 9Builders: $150,000 to $350,000 in San Jose[14]
  • IMKAT Homes: $205,000 to $415,000 by size[15]
  • ADU Builders Group: $450 to $475 per sq ft[16]
  • SYMBiHOM: $250,000 to $500,000 for a 500 to 1,200 sq ft backyard ADU[13]

None of these pages cites where its number comes from.

Common questions

How much does it cost to build an ADU in Los Gatos?

For a 750 sq ft detached ADU, our estimate is $350,000 to $465,000 to build. School and utility fees can add more.[1][2][3][4]

What are the ADU permit fees in Los Gatos?

The city doesn't publish a total. No published total; see fee lines The fee lines on this page list each charge.[1]

Do ADUs under 750 sq ft pay impact fees?

No. State law bars impact fees on ADUs under 750 sq ft. Larger ADUs pay in proportion to the main home. School fees follow a different rule, and districts disagree about it, so ask yours.[17]

Is a garage conversion cheaper than a new ADU?

Usually. In the 2021 UC Berkeley survey, garage ADUs had a median cost of $90,000 statewide against $180,000 for detached ones. Raised to 2026 prices, a 400 sq ft garage conversion lands around $120k to $225k by our estimate.[2][3][13]

Los Gatos ADU rules and builders Compare fees across cities

Sources

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

  1. 1. Town of Los Gatos Building valuation method, plan review 65%, Traffic Impact Mitigation Fee $1,128/ADT, construction taxes Checked Oct 18, 2026
  2. 2. UC Berkeley Center for Community Innovation Statewide median $150,000/$250sf Checked Oct 18, 2026 read from an archived copy of this official page
  3. 3. California Department of General Services California Construction Cost Index (ENR BCI average of San Francisco and Los Angeles) Checked Oct 18, 2026
  4. 4. San Mateo County ADU Resource Center $450-$600/sf all-in placeholder Checked Oct 18, 2026
  5. 5. Abodu Home From $234,800 Checked Oct 18, 2026
  6. 6. Town of Los Gatos Planning plan check 20% of building fee Checked Oct 18, 2026
  7. 7. Town of Los Gatos 1,200 sq ft max Checked Oct 18, 2026
  8. 8. Los Gatos Union SD Residential $4.07/sq ft Checked Oct 18, 2026
  9. 9. Los Gatos-Saratoga Union HSD $1.66/sq ft as of June 15, 2026 Checked Oct 18, 2026
  10. 10. Campbell Union HSD $1.61/sq ft eff Checked Oct 18, 2026
  11. 11. West Valley Sanitation District ADU connection $6,727 max/$511.16 per DFU Checked Oct 18, 2026
  12. 12. San Jose Water Water Services Department works with homeowners on new service Checked Oct 18, 2026
  13. 13. SYMBiHOM Garage conversion $150K-$225K Checked Oct 18, 2026
  14. 14. 9Builders FAQ: SJ ADU $150k-$350k, rents $1,800-$3,000/mo, unsourced Checked Oct 18, 2026
  15. 15. IMKAT Size-tier cost table $205k-$415k, unsourced Checked Oct 18, 2026
  16. 16. ADU Builders Group $450-$475/sq ft Checked Oct 18, 2026
  17. 17. 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