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What an ADU costs in Palo Alto

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

$7,346

Detached ADU building permit (flat 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 $357k to $472k for a 750 sq ft detached ADU. Adjust it for your lot

13 licensed builders list Palo Alto 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 Palo Alto'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 Palo Alto

All 13

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

Every fee Palo Alto can charge

Detached ADU building permit $7,346 per permit; $2,653 for a master-plan permit[1] Site-specific permits tied to a master plan: $3,929 for prefab, $5,481 for site-built.
Plan checks Building plan check 125% of the permit fee; planning and public works plan checks 35% each[1] The schedule does not say whether these apply on top of the flat ADU fee.
City guidebook ranges $2,000 to $8,000 in building permit fees; $10,000 to $80,000 in impact fees[6] Impact fees apply only at 750 sq ft and up.
Development impact fees (parks, community center, library, public safety, general government) $0 under 750 sq ft. At 750 sq ft and up, a share of the single-family rates: parks $18.75, community center $1.44, libraries $0.86 per sq ft; public safety $1,383 and general government $1,743 per unit[7][1] The share is in proportion to the size of the main home. JADUs and garage conversions with no added floor area are exempt.
School fees Palo Alto Unified $4.79 per sq ft; Los Altos SD $3.58 per sq ft[8][9][10][6] Only for ADUs over 500 sq ft. You pay the district directly; the city does not collect it.
Water capacity charge (City of Palo Alto Utilities) $3,750 for a 5/8 x 3/4-inch meter; $6,250 for a 1-inch meter[1][11] Charged when CPAU requires a new service. A JADU is not a separate unit for water, sewer or power.
Wastewater capacity charge (City of Palo Alto Utilities) $5,250 for a 4-inch connection with a 5/8-inch meter; $10,500 with a 1-inch meter[1]

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)[12] $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[13]
  • IMKAT Homes: $205,000 to $415,000 by size[14]
  • ADU Builders Group: $450 to $475 per sq ft[15]
  • SYMBiHOM: $250,000 to $500,000 for a 500 to 1,200 sq ft backyard ADU[12]

None of these pages cites where its number comes from.

Common questions

How much does it cost to build an ADU in Palo Alto?

For a 750 sq ft detached ADU, our estimate is $350,000 to $465,000 to build, plus about $7,346 in city fees by the city's own numbers. School and utility fees can add more.[1][2][3][4]

What are the ADU permit fees in Palo Alto?

The city's own estimate is $7,346 (detached adu building permit (flat fee)). School and utility fees are separate.[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.[16]

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][12]

Palo Alto 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. City of Palo Alto ADU flat permit fees, sf-based building fees, plan check %, impact fees, CPAU capacity charges 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. City of Palo Alto Cost & fee ranges, school $4.79/SF, timeline phases, parking Checked Oct 18, 2026
  7. 7. City of Palo Alto SF impact fee rates Checked Oct 18, 2026
  8. 8. City of Palo Alto PAUSD and LASD Checked Oct 18, 2026
  9. 9. Palo Alto Unified School District $4.79/sf residential as of July 9, 2022 Checked Oct 18, 2026
  10. 10. Los Altos School District $3.58/sf residential Checked Oct 18, 2026
  11. 11. City of Palo Alto (American Legal Publishing, official code host) PAMC 18.09.040-18.09.050: Table 2 local-standard units: 900 sq ft (1,000 sq ft with 2+ bedrooms), attached max Checked Oct 18, 2026
  12. 12. SYMBiHOM Garage conversion $150K-$225K Checked Oct 18, 2026
  13. 13. 9Builders FAQ: SJ ADU $150k-$350k, rents $1,800-$3,000/mo, unsourced Checked Oct 18, 2026
  14. 14. IMKAT Size-tier cost table $205k-$415k, unsourced Checked Oct 18, 2026
  15. 15. ADU Builders Group $450-$475/sq ft Checked Oct 18, 2026
  16. 16. 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