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San José ADU Cost & Permit Fee Calculator

A 600 sq ft ADU in San José runs about $334,000 all in, $9,519 of it city and school fees. Price your own build, fees and rental payback.

Updated · By Niraj Kumar · 11 sources

1. The ADU

Type of ADUType of ADU
sq ft
1501,200

School fees start above 500 sq ft and impact fees at 750 sq ft.

Finish levelFinish level
sq ft

Impact fees from 750 sq ft are scaled by the ADU's size against the house.

2. Site work

ft

Distance from the house's sewer lateral to the ADU.

ft
ft
Main electrical panel upgradeMain electrical panel upgrade
%
0%25%

Architect, structural engineer, Title 24 and survey, as a share of the build. About 4% with a city pre-approved plan.

%
0%30%

3. San José fees

$

San José fee schedule.

$

Waived: under 750 sq ft (state law).

$

Charged on new detached and attached units.

$

$5.38 a sq ft on the whole unit.

4. Rent and financing

Rented asRented as
$

HUD's FY 2026 fair market rent for the metro, a conservative figure. Enter a local listing to replace it.

%
0%50%
%

Charged on the ADU's construction cost only; the house is not reassessed.

$
% of rent
0%30%
How you payHow you pay
years
5 yrs30 yrs
%

Net rent ÷ cap rate is how appraisers value income. 4-6% is typical for California rentals.

Total cost, San José$333,707$556 a sq ft, $9,519 of it fees

At 500 sq ft it would pay no school fees, saving $3,228.

Construction
$324,188
build, site work, design and contingency
City and school fees
$9,519
Monthly cash flow, year one
$2,222
on $2,982 rent
Payback
10.7 years
8% cash-on-cash in year one
Value added
$533,320
$199,614 more than it costs, at a 5% cap rate
Where the money goes600 sq ft detached ADU, standard finish
  1. 1Construction$262,500
  2. 2Contingency$27,563
  3. 3Design and engineering$21,000
  4. 4Utility trenching$13,125
  5. 5Permit and plan check$3,291
  6. 6School fees$3,228
  7. 7Sewer and water capacity$3,000
Cumulative cash flow from rentStill to recoverAhead
$-400 K$-200 K$0$200 K$400 KPayback, year 10.7048121620
Year-by-year rent and cash flowShow
YearRent collectedRunning costsLoanCash flowCumulative
1$33,995$7,329$0$26,666-$307,040
2$35,015$7,513$0$27,502-$279,539
3$36,065$7,702$0$28,363-$251,176
4$37,147$7,896$0$29,251-$221,925
5$38,261$8,095$0$30,166-$191,758
6$39,409$8,299$0$31,110-$160,648
7$40,592$8,509$0$32,083-$128,565
8$41,809$8,724$0$33,085-$95,480
9$43,064$8,945$0$34,119-$61,361
10$44,356$9,171$0$35,184-$26,177
11$45,686$9,404$0$36,282$10,105
12$47,057$9,642$0$37,414$47,520
13$48,468$9,887$0$38,581$86,101
14$49,923$10,139$0$39,784$125,885
15$51,420$10,397$0$41,023$166,908
16$52,963$10,662$0$42,301$209,209
17$54,552$10,934$0$43,618$252,827
18$56,188$11,213$0$44,976$297,803
19$57,874$11,499$0$46,375$344,178
20$59,610$11,793$0$47,817$391,995

How the San José ADU Cost & Permit Fee Calculator works

A new 600 sq ft detached ADU in San José costs about $334,000 to build in 2026, including $9,519 in permit, capacity and school fees. Impact fees do not apply under 750 sq ft. Rented at $2,982 a month, it pays back in about 11 years.

Cost = sq ft × rate₍type, finish₎ × city index + utility runs + panel + design + contingency + fees fees = permit + impact × (ADU ÷ house, from 750 sq ft) + capacity (new builds) + school × sq ft (over 500) Payback: Σ₍y₎ (rent × (1 − vacancy) − tax − insurance − upkeep − loan) ≥ cash invested

This page uses the same method as the California ADU Cost & ROI Calculator, which explains each term and assumption in full.

Worked example

A 600 sq ft detached one-bedroom ADU at standard finish behind a 1,600 sq ft house in San José, with utility lines run 50 ft from the house, paid in cash.

  1. 1Construction: 600 sq ft at about $438 a sq ft is $262,500; utility trenching adds $13,125, design $21,000 and a 10% contingency $27,563
  2. 2Fees: $3,291 in permit and plan check, no impact fees (under 750 sq ft), $3,000 in sewer and water capacity, and $3,228 in school fees
  3. 3Rent of $2,982 a month less 5% vacancy, property tax, insurance and upkeep leaves $26,666 a year

The ADU costs about $333,707 all in, $556 a sq ft, of which $9,519 is fees. The rent repays it in about 10.7 years, a 8.0% cash return in the first year.

Frequently asked questions

How much are ADU permit fees in San José?

For a new 600 sq ft detached ADU, city and school fees come to about $9,519: $3,291 in permit and plan check, $3,000 in sewer and water capacity charges and $3,228 in school fees. At 800 sq ft they rise to about $21,407, including $9,000 in impact fees. Going from 749 to 750 sq ft alone adds about $10,255. A garage conversion pays a smaller permit fee and no capacity charge.

How much does it cost to build an ADU in San José?

About $334,000 for a 600 sq ft detached ADU at standard finish, all in, or $556 a sq ft, and about $449,000 for 800 sq ft. Rented as a one-bedroom at $2,982 a month, the HUD fair market rent for the area, it would repay a cash build in about 10.7 years. A garage conversion typically costs 35-45% less.

What is unusual about ADU fees in San José?

The FY 2026-27 schedule sets flat ADU fees: $3,291 for permit issuance, plan review and inspection up to 750 sq ft, $5,103 from 751 to 1,200. Parkland fees apply from 750 sq ft, scaled to the house; that figure is an estimate.

Sources

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