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Riverside ADU Cost & Permit Fee Calculator

A 600 sq ft ADU in Riverside runs about $255,000 all in, $8,228 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. Riverside fees

$

Riverside 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, Riverside$254,611$424 a sq ft, $8,228 of it fees

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

Construction
$246,383
build, site work, design and contingency
City and school fees
$8,228
Monthly cash flow, year one
$1,178
on $1,700 rent
Payback
14.5 years
5.6% cash-on-cash in year one
Value added
$282,756
$28,145 more than it costs, at a 5% cap rate
Where the money goes600 sq ft detached ADU, standard finish
  1. 1Construction$199,500
  2. 2Contingency$20,948
  3. 3Design and engineering$15,960
  4. 4Utility trenching$9,975
  5. 5School fees$3,228
  6. 6Permit and plan check$3,000
  7. 7Sewer and water capacity$2,000
Cumulative cash flow from rentStill to recoverAhead
$-300 K$-200 K$-100 K$0$100 K$200 KPayback, year 14.5048121620
Year-by-year rent and cash flowShow
YearRent collectedRunning costsLoanCash flowCumulative
1$19,380$5,242$0$14,138-$240,473
2$19,961$5,372$0$14,589-$225,884
3$20,560$5,506$0$15,054-$210,829
4$21,177$5,643$0$15,534-$195,295
5$21,812$5,783$0$16,029-$179,266
6$22,467$5,928$0$16,539-$162,727
7$23,141$6,075$0$17,065-$145,662
8$23,835$6,227$0$17,608-$128,054
9$24,550$6,383$0$18,167-$109,887
10$25,287$6,543$0$18,744-$91,143
11$26,045$6,707$0$19,339-$71,805
12$26,826$6,875$0$19,952-$51,853
13$27,631$7,047$0$20,584-$31,269
14$28,460$7,224$0$21,236-$10,033
15$29,314$7,406$0$21,908$11,875
16$30,193$7,592$0$22,601$34,476
17$31,099$7,784$0$23,316$57,792
18$32,032$7,980$0$24,052$81,844
19$32,993$8,181$0$24,812$106,656
20$33,983$8,388$0$25,595$132,251

How the Riverside ADU Cost & Permit Fee Calculator works

A new 600 sq ft detached ADU in Riverside costs about $255,000 to build in 2026, including $8,228 in permit, capacity and school fees. Impact fees do not apply under 750 sq ft. Rented at $1,700 a month, it pays back in about 14 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 Riverside, with utility lines run 50 ft from the house, paid in cash.

  1. 1Construction: 600 sq ft at about $333 a sq ft is $199,500; utility trenching adds $9,975, design $15,960 and a 10% contingency $20,948
  2. 2Fees: $3,000 in permit and plan check, no impact fees (under 750 sq ft), $2,000 in sewer and water capacity, and $3,228 in school fees
  3. 3Rent of $1,700 a month less 5% vacancy, property tax, insurance and upkeep leaves $14,138 a year

The ADU costs about $254,611 all in, $424 a sq ft, of which $8,228 is fees. The rent repays it in about 14.5 years, a 5.6% cash return in the first year.

Frequently asked questions

How much are ADU permit fees in Riverside?

For a new 600 sq ft detached ADU, city and school fees come to about $8,228: $3,000 in permit and plan check, $2,000 in sewer and water capacity charges and $3,228 in school fees. At 800 sq ft they rise to about $15,304, including $4,000 in impact fees. Going from 749 to 750 sq ft alone adds about $5,755. A garage conversion pays a smaller permit fee and no capacity charge.

How much does it cost to build an ADU in Riverside?

About $255,000 for a 600 sq ft detached ADU at standard finish, all in, or $424 a sq ft, and about $340,000 for 800 sq ft. Rented as a one-bedroom at $1,700 a month, the HUD fair market rent for the area, it would repay a cash build in about 14.5 years. A garage conversion typically costs 35-45% less.

What is unusual about ADU fees in Riverside?

Building and Safety permit and plan check run about $1,400-$1,500 for an 800 sq ft ADU, plus a $289 zoning check and surcharges; the city put all-in fees at $3,000-$9,000. Impact and capacity figures are estimates.

Sources

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