Skip to content
Bay Area ADU Builders
Get quotes

What an ADU costs in Mountain View

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

Still choosing the scope? Compare ADU remodeling, garage conversion and new construction in Mountain View before using the estimator.

Official City fees

Line by line

$7,000 to $13,000 in building permit fees, including inspectionsSee 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

13 licensed builders list Mountain View on their own sites. Your quote request goes to the Bay Area ADU Builders team.

Get 3 quotes

Estimate your ADU

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

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

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.

Get 3 quotes to check this number

Licensed builders who list Mountain View

All 13

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

Every fee Mountain View can charge

Building permit, new ADU (city's typical range) $7,000 to $13,000[1] Based on a construction valuation of $100,000 to $300,000; includes inspections. Conversions run $3,000 to $5,000 and a JADU $4,000 to $6,000.
Excavation permit, if you need utility or sidewalk work Up to $12,000[1]
Land use document fee 0.24% of construction valuation[6] Collected on all projects at building permit.
Citywide transportation fee $6,273.15 per new single-family unit[6][7] The city's page has no ADU line. State law: no impact fees under 750 sq ft; above that, a share in proportion to the main home.
Park land in-lieu fee Based on land value: $160 to $210 per sq ft of land at low density[6][7] The page does not say how this applies to ADUs. State law bars it under 750 sq ft.
School fees Mountain View Whisman $3.45, Los Altos SD $3.58, MVLA high school $1.72 per sq ft[8][1][9][10][11] For 500 sq ft or more. You pay the districts directly and show the receipt before the permit is issued. MVLA rises to $1.79 on Nov 13, 2026.
Water capacity fee (City of Mountain View) $9,389.06 per single-family detached unit[6][7][1] No ADU line. State law limits capacity charges to a share based on the ADU's size or plumbing fixtures. Conversions that fix a code or zoning problem pay none unless new utility work is needed.
Sewer capacity fee (City of Mountain View) $7,922.69 per single-family detached unit[6][7] No ADU line. The same state proportionality rule applies.

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 Mountain View?

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 Mountain View?

The city doesn't publish a total. $7,000 to $13,000 in building permit fees, including inspections 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.[7]

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]

Mountain View 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 Mountain View ADU page: single-family ADU zoning table (850 sq ft studio/1 bedroom, 1,000 sq ft 2+ bedrooms, attached max 50 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 Mountain View Development fees effective Aug 22, 2026: water capacity $9,389.06 and sewer capacity $7,922.69 per single-fami Checked Oct 18, 2026
  7. 7. 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
  8. 8. City of Mountain View School impact fees for new construction, conversion or additions of 500 sq ft or more Checked Oct 18, 2026
  9. 9. Mountain View Whisman SD $3.45/sf residential effective July 1, 2024 Checked Oct 18, 2026
  10. 10. Los Altos School District $3.58/sf residential Checked Oct 18, 2026
  11. 11. Mountain View-Los Altos Union HSD MVLA share $1.72/sf 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