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San Diego ADU Cost & Permit Fee Calculator

A 600 sq ft ADU in San Diego runs about $309,000 all in, $23,450 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 Diego fees

$

San Diego 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 Diego$308,735$515 a sq ft, $23,450 of it fees

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

Construction
$285,285
build, site work, design and contingency
City and school fees
$23,450
Monthly cash flow, year one
$1,803
on $2,459 rent
Payback
12 years
7% cash-on-cash in year one
Value added
$432,676
$123,941 more than it costs, at a 5% cap rate
Where the money goes600 sq ft detached ADU, standard finish
  1. 1Construction$231,000
  2. 2Contingency$24,255
  3. 3Design and engineering$18,480
  4. 4Permit and plan check$16,121
  5. 5Utility trenching$11,550
  6. 6Sewer and water capacity$4,101
  7. 7School fees$3,228
Cumulative cash flow from rentStill to recoverAhead
$-400 K$-200 K$0$200 K$400 KPayback, year 12.0048121620
Year-by-year rent and cash flowShow
YearRent collectedRunning costsLoanCash flowCumulative
1$28,033$6,399$0$21,634-$287,101
2$28,874$6,559$0$22,314-$264,787
3$29,740$6,724$0$23,016-$241,771
4$30,632$6,893$0$23,739-$218,033
5$31,551$7,067$0$24,484-$193,548
6$32,497$7,245$0$25,253-$168,296
7$33,472$7,427$0$26,045-$142,251
8$34,477$7,615$0$26,862-$115,389
9$35,511$7,807$0$27,704-$87,685
10$36,576$8,005$0$28,571-$59,114
11$37,673$8,207$0$29,466-$29,648
12$38,804$8,415$0$30,388$740
13$39,968$8,629$0$31,339$32,079
14$41,167$8,848$0$32,319$64,398
15$42,402$9,073$0$33,329$97,727
16$43,674$9,303$0$34,370$132,098
17$44,984$9,540$0$35,444$167,542
18$46,334$9,783$0$36,550$204,092
19$47,724$10,033$0$37,691$241,782
20$49,155$10,289$0$38,866$280,648

How the San Diego ADU Cost & Permit Fee Calculator works

A new 600 sq ft detached ADU in San Diego costs about $309,000 to build in 2026, including $23,450 in permit, capacity and school fees. Impact fees do not apply under 750 sq ft. Rented at $2,459 a month, it pays back in about 12 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 Diego, with utility lines run 50 ft from the house, paid in cash.

  1. 1Construction: 600 sq ft at about $385 a sq ft is $231,000; utility trenching adds $11,550, design $18,480 and a 10% contingency $24,255
  2. 2Fees: $16,121 in permit and plan check, no impact fees (under 750 sq ft), $4,101 in sewer and water capacity, and $3,228 in school fees
  3. 3Rent of $2,459 a month less 5% vacancy, property tax, insurance and upkeep leaves $21,634 a year

The ADU costs about $308,735 all in, $515 a sq ft, of which $23,450 is fees. The rent repays it in about 12.0 years, a 7.0% cash return in the first year.

Frequently asked questions

How much are ADU permit fees in San Diego?

For a new 600 sq ft detached ADU, city and school fees come to about $23,450: $16,121 in permit and plan check, $4,101 in sewer and water capacity charges and $3,228 in school fees. At 800 sq ft they rise to about $24,526. Going from 499 to 500 sq ft alone adds about $10,020 as the permit fee moves to its larger tier. A garage conversion pays a smaller permit fee and no capacity charge.

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

About $309,000 for a 600 sq ft detached ADU at standard finish, all in, or $515 a sq ft, and about $401,000 for 800 sq ft. Rented as a one-bedroom at $2,459 a month, the HUD fair market rent for the area, it would repay a cash build in about 12.0 years. A garage conversion typically costs 35-45% less.

What is unusual about ADU fees in San Diego?

Plan check, building permit and miscellaneous fees jump at 500 sq ft: about $6,100 below and $16,100 above. Sewer capacity is $2,577 and water capacity $1,524 at any size; a new meter adds the County Water Authority charge of $5,859 or more.

Sources

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