Riverside County ADU Guide 2026
How Much Does an ADU Cost in Riverside County?
A 600 sq ft detached ADU in Riverside County runs $89,000–$195,800. Get your number in about 2 minutes.
ADU Cost by Type and Size (Riverside County)
A detached ADU in Riverside County typically runs $89,000–$195,800 for 600 square feet and a garage conversion $44,900–$98,500. Attached and junior ADUs are quoted by the contractor. Builders price from published construction cost guides adjusted for Riverside County labor; GetProEstimate shows you that number for your lot first, then one licensed Riverside County contractor quotes to the same scope you saw.
Detached ADU, 400 sq ft
$71,800–$157,800
Studio. Standard to high-end finishes.
Detached ADU, 600 sq ft
$89,000–$195,800
One bedroom. Standard to high-end finishes.
Detached ADU, 800 sq ft
$106,000–$233,500
Two bedroom. Standard to high-end finishes.
Garage Conversion, 400 sq ft
$44,900–$98,500
With a kitchen and bath. Standard to high-end finishes.
Source: the construction cost guides contractors bid from, adjusted for Riverside County labor. Low end = standard finish, high end = high-end finish.
What Drives the Price in Riverside County
Type and size: 750 sq ft is the line for impact fees, 500 sq ft for school fees.
Utility runs, and septic on rural and desert lots: a septic system instead of a sewer connection changes the budget.
Heat: insulation and AC sizing matter more inland.
Lot size, which is larger here and makes detached units easier to site.
Your city’s or the County’s plan-check fees.
Demand is strongest on the Riverside and Corona side. In the state’s permit records for 2023 to 2025, the city of Riverside issued 792 ADU permits, Moreno Valley 237, Jurupa Valley 223 and Corona 207, and Corona more than doubled from 42 in 2023 to 84 in 2025. Temecula and Murrieta together issued 105 over the same three years. Source: California HCD Housing Element Annual Progress Reports, Table A2.
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Frequently Asked Questions
How much does an ADU cost in Riverside County?
$89,000 to $195,800 for a 600 square foot detached ADU, $71,800 to $157,800 at 400 square feet and $106,000 to $233,500 at 800, from standard to high-end finishes; a 400 square foot garage conversion runs $44,900 to $98,500. Attached and junior ADUs are quoted by the contractor. The estimate prices your lot from your address and your answers.
Which Riverside County cities build the most ADUs?
By the state’s permit records for 2023 to 2025: Riverside 792, Moreno Valley 237, Jurupa Valley 223 and Corona 207. Temecula and Murrieta together issued 105.
Can my HOA stop me from building an ADU in Riverside County?
No. California law voids HOA rules that prohibit or unreasonably restrict an ADU or junior ADU on a single-family lot; reasonable design rules are allowed.
Do I pay impact fees on an ADU in Riverside County?
Not on an ADU under 750 square feet; larger ADUs pay fees in proportion to the main house. School district fees apply only above 500 square feet. Permit and plan-check fees still apply.
How long does an ADU permit take in Riverside County?
State law gives the city or the County 60 days to approve or deny a complete ADU application. Lots on septic add a health department review.
Why does the estimate differ from a builder’s quote?
The estimate is the published cost-guide price adjusted for Riverside County labor; a quote is one builder’s price for one design. The licensed Riverside County contractor you work with through GetProEstimate quotes to the same scope you saw.
Ready to see your number?Run your own estimate in about two minutes. No credit check.Who you’ll work with: a licensed Riverside County contractor for your trade, holding a California CSLB license you can look up before the appointment.
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