ADU Constructionin Rialto, CA
ADU construction in Rialto is ministerial: the City must approve or deny a complete application within 60 days, and state law now sets 15 business days for a completeness check. Rialto's ordinance dates from 2020, so state law leads where they differ. Two City pages disagree on plan check, 30 business days or 20.
Rialto is mostly single-family neighborhoods, which is the housing backyard units were designed for. The Census Bureau's 2024 one-year estimates put 72.3 percent of its 27,511 homes in single-family detached houses, 19,878, and the median owner-occupied home at $543,300, plus or minus $22,508. The City's history page dates the townsite to 1887 and incorporation to 1911, and 35.0 percent of today's homes came from the 1980s, so most lots hold a tract-era house with a garage that predates every ADU law.
Rialto's ADU ordinance, Municipal Code 18.10.070, dates from July 14, 2020 (Ordinance 1641), so this page leads with state law and then shows where the City's text and handouts add to it. It covers the clocks, sizes and types, garage conversions, the 210 Freeway line, unpermitted units and lot splits, and utilities and schedule. Code text here comes from GoCodebook, a third-party mirror, so confirm each rule with Building & Safety and the City's ADU page. Price ranges and phases are on our ADU construction page.
What Rialto's code and ADU page say about a backyard or garage unit
Where adu construction permits come from in Rialto: City of Rialto Community Development Department, Building & Safety Division.
- Rialto's ADU ordinance is Municipal Code 18.10.070 (Ordinance 1641, July 14, 2020, read in the GoCodebook mirror): ADUs are permitted on all single-family and multifamily lots, must be ministerially approved or denied within 60 days of a complete application, are limited to one ADU plus one JADU per single-family lot, 16 feet or one story, 4 foot side and rear setbacks, at most 50 percent of the primary home or 850 square feet (1,000 if more than one bedroom) and never over 1,200 square feet, and ADUs under 750 square feet pay no development impact fees. The code text predates later state ADU changes, so confirm current limits with Planning.
- ADU process on the City page (updated 2026-09-21): apply for an Address Letter through Planning in the OPC (currently no fee), then submit to Building and Safety with Title 24, a solar PV plan for new detached units, fire sprinkler plans if applicable and a Hold Harmless Agreement; plan check is scheduled within 30 business days. An older Planning page copy still says 20 business days plus 10 for permit processing, so the newer figure is used. A school fee letter is required regardless of size and districts usually charge for ADUs over about 500 square feet.
- The City's pre-selected ADU plans come from Design Path Studios (plans owned by Menifee and Chino), which the City page says cost $5,000 to $7,000 to license; sprinklers are required if the main house has them, in a Very High Fire Hazard Severity Zone or for a new house with an ADU, setbacks under 5 feet need fire-rated walls if unsprinklered, detached ADUs need their own gas, water and electric meters, and a unit in a Very High zone must meet WUI construction rules.
- Two-unit projects under Government Code 65852.21 are handled by Municipal Code 18.113 (Ordinance 1665, February 8, 2022): the applicant needs a Subdivision Map Act certificate of compliance, the City tells the applicant in writing within 30 days if the application is incomplete, and a City fee applies. (GoCodebook mirror)
Build an ADU in Rialto: does state law or Ordinance 1641 govern?
State law governs wherever the two differ, and the gap is real because Rialto's ordinance is more than five years old. Government Code 66317 requires ministerial approval with no hearing, a written completeness decision within 15 business days under the changes that took effect January 1, 2026, and approval or denial within 60 days of a complete application, or the permit is deemed approved. Rialto's ordinance already says 60 days, so those clocks agree, but the 15 business day check is newer than its text.
Size is the other place to watch. Government Code 66321 bars a city from setting its maximum below 850 square feet, or 1,000 if the unit has more than one bedroom, and requires it to allow an 800 square foot detached unit with 4 foot side and rear setbacks. Rialto's numbers sit at or above those floors, which is a good sign, though the ordinance predates the 2026 state changes, including the renumbering that moved the impact fee rule to Section 66311.5. If a plan check comment cites a local limit below a state floor, we ask for the code section in writing.
Code text here is the third-party GoCodebook mirror as of October 4, 2026, so treat it as unofficial.
How long does an ADU permit take in Rialto: 30 business days, 20 or 60 days?
The City's two ADU pages disagree, and both are public. The Building & Safety page, updated September 21, 2026, says plan check is scheduled within 30 business days and that applications go through the Online Permitting Center. An older copy on the Planning side, dated January 6, 2025, says 20 business days for plan check plus 10 for permit processing and takes applications by email. The older figure also totals 30 business days, though it counts processing, so the pages may describe different stretches, and the code's 60-day ministerial deadline sits above both.
The sequence on the newer page starts with an Address Letter from Planning, requested in the portal and currently free, followed by the Building & Safety submittal. That package carries Title 24 energy compliance, a solar photovoltaic plan for a new detached unit, fire sprinkler plans if they apply and a Hold Harmless Agreement. We build the package from the newer page, ask the counter which page governs your file, and keep the state's 15 business day and 60 day deadlines on the calendar as backstops.
A correction round slows everything, so a complete first submittal is the real schedule saver.
How big can an ADU be in Rialto, and which types need only a building permit?
Under Ordinance 1641 a single-family lot may have one ADU plus one junior unit, and the ADU can be 16 feet or one story tall with 4 foot side and rear setbacks. Its size runs up to 50 percent of the primary home or 850 square feet, 1,000 with more than one bedroom, and never above 1,200 square feet. Units under 750 square feet pay no development impact fees, which matches the state rule.
State law adds four protected types that a city must approve with only a building permit: a house or garage conversion with a junior unit, one detached unit up to 800 square feet, conversions of non-livable multifamily space, and up to eight detached units on a lot with an existing multifamily building. A junior unit tops out at 500 square feet inside the house, and owner occupancy is required only where it shares a bathroom with the main home.
Ordinary R-1 rules matter too. Municipal Code 18.10.030 sets an 8,400 square foot minimum lot, 30 percent building coverage and a 25 foot front yard, while state law has no minimum lot size for an ADU and still guarantees an 800 square foot unit. We ask Planning how it counts a unit against that 30 percent before anything is drawn.
Can I convert my Rialto garage into an ADU, and must I replace the parking?
Yes, and no replacement parking is required. Government Code 66322 and 66314 say a city may not demand parking back when a garage, carport or covered structure is converted or demolished for an ADU, and a converted structure needs no new setbacks. That makes a 1980s tract garage the cheapest route to a unit, but the City's page lists what comes with it: sprinklers if the main house has them, fire-rated walls where an unsprinklered unit sits under 5 feet from a line, and separate gas, water and electric meters for a detached unit.
One of those items may collide with state law. Government Code 66311.5 says a unit converted from existing space cannot be forced into a new utility connection or a related fee, so we ask the counter which rule wins for a garage conversion before ordering a meter. Rule 1403 of the South Coast AQMD also calls for an asbestos survey before renovation, and Rialto's handout says the only owner exemption is a single-family homeowner who lives in the house and does the work personally.
Does the 210 Freeway line or a fire zone change an ADU in Rialto?
It can. North of the 210 is where the City's own handout puts the Wildland-Urban Interface and the Special Wind Region. North of the line the design wind speed is 120 mph for Risk Category II, against 96 mph south of it, and Municipal Code 15.08 requires a Class A roof, where south of the line Class A, B or C is allowed. A new detached unit north of the freeway carries those roof and wind assumptions from the first sheet of the plans.
Fire zones are a separate layer. The State Fire Marshal issued recommended Local Responsibility Area maps for San Bernardino County on March 24, 2025, and Rialto Fire, the City's own department rather than the County Fire District, says it is not proposing increases. We could not tell which parcels fall in which zone, so check your address in the State's map. The City says a unit in a Very High zone needs sprinklers and WUI construction, and that owners there must keep 100 feet of defensible space.
Your parcel's fire zone is not something we could confirm from here, so the State's map and Rialto Fire decide.
Can an unpermitted backyard unit be legalized in Rialto, and what about a two-unit lot split?
Possibly, and state law helps. Government Code 66311.7, formerly 66332, says a city cannot deny a permit for an unpermitted ADU built before January 1, 2020 over building-code or ordinance violations unless the unit is substandard under Health and Safety Code 17920.3, and it allows a confidential third-party inspection. Rialto's code leans the other way: Municipal Code 15.08.030 makes it unlawful to own or use an unpermitted structure and requires a special investigation before a permit for work started without one.
The wrinkle is spillover. The City's Re-Roof handout screens out unpermitted structures, so an old converted shed or patio enclosure can block a re-roof permit on the same lot. Two-unit projects under Government Code 65852.21 are handled by Municipal Code 18.113, from Ordinance 1665 of February 8, 2022: the applicant needs a Subdivision Map Act certificate of compliance, and the City tells the applicant in writing within 30 days if the application is incomplete.
Rialto also adopted a Housing Opportunity District in 2026 to carry out its Housing Element, which must zone for 8,272 units, and the City's site inventory is searchable by address or parcel number. Ask Planning whether your parcel sits inside it.
What do meters, fees and construction time add to a Rialto ADU?
The City's page asks detached units for their own gas, water and electric meters, and Edison meter releases are not done on Fridays, so we aim electrical finals at another weekday. No impact fee applies to a unit of 750 square feet or less, and the City requires a school fee letter regardless of size, with districts usually charging for ADUs over about 500 square feet. We found no dollar figure for plan check or permit fees, because Rialto's schedule is a 2022 table that predates the 2025 codes.
The City's pre-selected plans come from Design Path Studios, which the page says cost $5,000 to $7,000 to license, and the plans are owned by Menifee and Chino, not Rialto. Our planning ranges are 4 to 10 weeks of design, the City's review, 2 to 6 weeks of scheduling and site prep, 3 to 5 months of construction for a garage conversion and 5 to 9 months for a detached unit, then 1 to 3 weeks of final inspections. Those phases are our estimates, and the City issues a Final, not a Certificate of Occupancy, for an ADU.
MDG Builders, CSLB #1040337, serves as the general contractor that designs, permits and manages the unit, and licensed subcontractors pour, frame, wire and plumb it, each able to show a license number and a certificate of insurance.
ADU photos from Rialto and nearby homes
Backyard cottages, garage conversions and utility work tied to Rialto, from flat tract lots south of the 210 to foothill sites north of it, in neighborhoods where garages from the 1980s boom are common. Tap a photo to enlarge it.
What adu construction costs around Rialto
Our ADU construction page prices a garage conversion to a studio or one bedroom at about $100,000 to $200,000 and a new detached unit of 400 to 800 square feet at about $200,000 to $400,000, built from three independent sources. None is a Rialto quote, since we found no Rialto study. UC Berkeley's survey of 2018 and 2019 projects reports a Los Angeles County median of $100,000, the Terner Center's 2020 estimate for Los Angeles is $148,000, and Remodeling magazine's 2025 Cost vs. Value report prices one Los Angeles ADU job at $178,536, of which 39.9 percent came back at resale. Wind design north of the 210, a fire sprinkler line, separate meters and the school fee letter can each add lines that a regional range misses, and the City's own charges appear separately in a written proposal. Our ADU cost guide shows how those ranges are built, and the ADU versus JADU guide explains the junior unit. For nearby work, see ADU construction in Fontana, San Bernardino and Los Angeles. A bath inside the unit is on our Rialto bathroom page, an attached project on the Rialto room addition page, windows on the Rialto window page, and the Rialto area page lists every trade we cover in the city.
| What it covers | Typical range |
|---|---|
| Garage conversion to a studio or one bedroom | $100,000 to $200,000 |
| New detached ADU, 400 to 800 sq ft | $200,000 to $400,000 |
| UC Berkeley survey, Los Angeles County median, 2018 and 2019 projects | $100,000 overall. $90,000 garage. $180,000 detached. |
| Terner Center and Berkeley CCI, 2020 | $148,000 Los Angeles estimate. $167,000 statewide average. |
| Remodeling Cost vs. Value 2025, Los Angeles | $178,536 job cost |
| Electrical and plumbing, Angi Los Angeles, January 2026 | Electrical $2,600 to $7,800. plumbing $3,900 to $10,400. |
| City permit and plan check fees | Not priced here |
Rialto ADU questions, answered
How long does it take to get an ADU permit in Rialto?
State law sets 15 business days for a completeness check and 60 days for a decision on a complete application, after which a missed deadline means deemed approval. Rialto's own pages say plan check within 30 business days on the newer one and 20 plus 10 on an older one, so ask the counter which applies to your file.
Do I need a permit to build an ADU in California?
Yes, every ADU needs a building permit, and the city must treat it ministerially, with no hearing. The state-protected types, such as a garage conversion with a junior unit or one detached unit up to 800 square feet, need only that building permit. In Rialto the process starts with an Address Letter from Planning in the Online Permitting Center.
How big can an ADU be in California?
A detached ADU can reach 1,200 square feet and an attached one up to half the existing house, though a city cannot set its maximum below 850 square feet, or 1,000 with more than one bedroom. Rialto's ordinance uses 850, 1,000 and 1,200, matching the state floors. A junior unit is limited to 500 square feet inside the house.
How much does it cost to convert a garage to an ADU?
Expect roughly $100,000 to $200,000 for a garage conversion to a studio or one bedroom, based on a UC Berkeley survey, a Terner Center estimate and Remodeling magazine's Cost vs. Value report, all Los Angeles area sources because we found no Rialto study. Slab condition, a new bathroom, panel and sewer work and any sprinkler line move the number.
What is the difference between an ADU and a JADU?
An ADU is a full second dwelling with its own kitchen and bath, up to 1,200 square feet detached, while a junior ADU is at most 500 square feet inside the existing house with an efficiency kitchen. A junior unit may share a bathroom with the main home, and owner occupancy applies only in that shared case.
Can I sell my ADU separately from my main house?
Generally no. State law bars separate sale of an ADU, with two exceptions: a qualified low-income buyer through a qualifying nonprofit, or a condominium ordinance the city has adopted. We found no Rialto condominium ordinance for ADUs in the pages we read, so assume the unit and the house sell together.
Do I need to replace parking when I convert my garage in Rialto?
No. State law bars a city from requiring replacement parking when a garage, carport or covered structure is converted or demolished for an ADU. A new unit may call for one space per unit or bedroom, whichever is less, unless an exemption applies, such as being within a half mile walk of transit, and tandem driveway parking can count.
Do I have to live on the property to rent an ADU?
No. A city cannot make an ADU owner live on the property under state law, though it may require rentals of 30 days or longer. A junior unit is the one exception, and only when it shares a bathroom with the main house. Homeowners association rules are a separate check, because state law limits what they may prohibit.
How do I build an ADU north of the 210 in Rialto?
Start with the roof and wind assumptions: north of the freeway the City requires a Class A roof and a 120 mph design wind speed, and a unit in a Very High fire zone needs sprinklers and WUI construction. Check your parcel in the State Fire Marshal's map, then ask Building & Safety what applies to the lot.
Can I convert my unpermitted garage into a legal ADU?
Often yes, but start with the records. State law protects units built before January 1, 2020 from denial over most code violations unless they are substandard, and a third-party inspection can be confidential. Rialto's code treats unpermitted structures as unlawful and requires a special investigation first, so expect that step before any permit issues.
Tell us about your Rialto ADU
Share which side of the 210 Freeway the lot is on, whether you want a garage conversion or a new detached unit, who lives on the property and roughly when the house was built, and our first visit starts with the plan check route and a fire zone question.