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
All in, before school and utility fees: about $355k to $470k for a 750 sq ft detached ADU. Adjust it for your lot
8 licensed builders list Redwood City on their own sites. Your quote request goes to the Bay Area ADU Builders team.
Get 3 quotes8 licensed builders list Redwood City on their own sites. Three quotes for your lot show where in the range you land. Your request goes to the Bay Area ADU Builders team.
Get 3 quotesChange the type and size. City fees come from Redwood City's own averages; the building cost is our estimate.
Building (middle) City fees School fees Parkland
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 numberThe top three by our public score for Redwood City. Some publish prices, which is the quickest check on the estimate above.
Based in Pleasanton, Alameda County
CSLB #1094866 active Class B Licensed 4 years
Based in Campbell, Santa Clara County
CSLB #638333 active Class B Licensed 34 years
Based in Santa Clara, Santa Clara County
CSLB #889458 active Class B Licensed 19 years
| Base permit fee, new ADU | $3,999.53 up to 400 sq ft or a garage conversion; $4,660.62 for 401 to 600 sq ft; $5,321.71 for 601 to 800 sq ft[1][2] Valuation-based fees are added case by case. |
|---|---|
| Transportation, park and housing impact fees | $0 for ADUs[1][7][8][2] A council resolution exempts ADUs from these three fees until April 1, 2027. The ADU page also says no impact fees under 750 sq ft. |
| School fees | $5.17 per sq ft, split between Sequoia Union HSD and your elementary district[7][9][10] For 500 sq ft or more of living space. You write two checks. |
| Wastewater collection capacity fee (City of Redwood City) | $1.78 per sq ft[1] The wastewater treatment capacity fee does not apply to ADUs. |
| Water capacity fee (City of Redwood City) | $3.19 per sq ft[1][7] The city says water and sewer capacity fees apply to ADUs. |
| Address for the ADU | $376[1] |
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.[3] 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).[4] We check that against two current numbers and use the spread as the range.
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.
Abodu published all-in prices (home + typical installation).[6]
Not included: Survey package ($6,000), trenching past 50 ft, crane past 100 ft, demolition, site engineering and sales tax.
None of these pages cites where its number comes from.
For a 750 sq ft detached ADU, our estimate is $350,000 to $465,000 to build, plus about $5,322 in city fees by the city's own numbers. School and utility fees can add more.[1][2][3][4][5]
The city's own estimate is $5,322 (base permit fee, new adu 601 to 800 sq ft). School and utility fees are separate.[1][2]
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.[15]
Every fact on this page links to one of these. We read each one on the date shown.