A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable ADU Builders Across Ontario
An ADU (accessory dwelling unit, or a second smaller home on your existing lot) in Ontario typically costs between $180,000 and $420,000 for a custom build, with prefab options starting closer to $130,000. We’re Lodgewick ADU Riverside, the ADU company of the Kingswell family, and we’ve been building detached units, garage conversions, and JADUs across Ontario since 2010. Our ADU Builders team knows Ontario’s lots, its overlay districts, and its permit process well enough to tell you the truth about your property before you spend a dime. Call (831) 292-4191 for a free estimate and a written price.
Every job runs under The Kingswell Guarantee: a written price before work starts, a real arrival window, a clean job site, and a written guarantee on the finished build. If something isn’t right within 365 days, we come back and make it right. No fine print. No phone tag.
Why Lodgewick ADU Riverside Is Ontario’s Preferred ADU Builders Company
Ontario homeowners don’t need another contractor who promises a lot and shows up with a different number. They need a builder who has actually worked on Euclid Avenue lots near the historic downtown, knows what Ontario’s building department asks for on a detached ADU, and can tell you whether your east-side HOA will allow the design you’re picturing. That’s us.
Led by Russ Delmar, our crew has built ADUs across Ontario, from the mid-century neighborhoods south of the 10 to the newer subdivisions near the 15. We coordinate scheduling from our Inland Empire office, with crews serving Ontario directly. When you call, a live person answers. Not a chatbot. Not a voicemail loop. That matters when you’re three weeks into a build and need a straight answer about an inspector’s note.
Our reputation in Ontario is built on what we put in writing: the price, the window, and the guarantee. The 365-Day Done Right Promise means if the work fails within a year, we come back free. No argument about whether it’s covered. It’s covered.
Detached ADU in Ontario
A Detached ADU is a fully separate dwelling unit built in the rear yard of your Ontario property, with its own entrance, kitchen, bath, and utility connections. On Ontario’s 6,000 to 10,000 square foot lots, a detached unit is usually the best use of space, especially for homeowners who want to rent to warehouse and distribution workers who need housing close to Ontario’s logistics hubs but don’t want a long commute.
What It Costs on a Typical Ontario Lot
A custom detached ADU in Ontario runs $220,000 to $420,000 depending on size, finish level, and site conditions. A 500-square-foot one-bedroom unit with standard finishes usually lands between $240,000 and $320,000. Prefab and modular units from brands like Abodu or Cover start lower, often $130,000 to $220,000 including site work, foundation, and utility connections.
Site Access and Staging
On tight lots, especially in the older neighborhoods around Euclid Avenue, access dictates a lot of the quote. If we can’t get equipment into the rear yard, we stage materials on the driveway and coordinate crane lifts over the existing structures. We did exactly that on a lot near the historic downtown, setting a prefab unit over the existing detached garage while keeping the neighbor’s parking spot open the entire time. That kind of logistics planning is part of what you’re paying for, and it’s part of why the written price we give you is the price you pay.
JADU in Ontario
A JADU (junior accessory dwelling unit) is a smaller unit, up to 500 square feet, built within the envelope of your existing home, often a converted garage, a finished basement, or an interior portion of the house. In Ontario, where many mid-century homes have attached garages that sit empty or hold storage, a JADU conversion is the most affordable path to rental income.
Pricing for a JADU Conversion
A garage-to-JADU conversion in Ontario typically runs $80,000 to $150,000 depending on the condition of the existing garage, the kitchen and bath scope, and whether your electrical panel needs upgrading. Many Ontario homes built in the 1950s and 60s have 100-amp panels. A JADU with a kitchen and mini-split system usually requires a panel upgrade to 200 amps, which adds $3,500 to $6,000 and can add two to three weeks to the schedule.
Party Walls and Notices
Converting an attached garage often means working against a wall you share with your own home, not a neighbor, so a formal party-wall notice isn’t typically required. But Ontario’s building department will want to see structural drawings for any wall or opening we modify. We handle that paperwork before we submit for permits, so you don’t get a correction notice mid-project.
Trusted Brands We Service in Ontario
We work directly with established prefab and panelized manufacturers like Abodu, Cover, and Dvele, and we specify James Hardie siding on most of our Ontario builds because it holds up to Ontario’s hot, dry summers without warping or fading. For Ontario customers, working with a brand-familiar crew means faster turnaround on submittals, fewer design conflicts, and a straightforward warranty process when something needs attention. We know which prefab models fit Ontario’s setback requirements and which ones trigger extra review on smaller lots.
Common ADU Builders Problems We See in Ontario Homes
- Skipping the overlay district check. Ontario has specific overlay zones, especially near the historic downtown, that add design review before permits are issued. We check those before we quote, so you’re not paying for a design that gets rejected.
- Ignoring east-side HOA CC&Rs. Newer subdivisions on Ontario’s east side often have HOAs that restrict exterior finishes, height, or detached structure placement. We pull those restrictions into the quote and design phase so the permit doesn’t stall later.
- Undersized electrical panels. Mid-century Ontario homes frequently have 100-amp panels. Adding a JADU or detached ADU with a mini-split and kitchen almost always requires 200 amps. We verify this in the first site visit, not during rough-in.
- Noise ordinance violations on dense lots. Ontario enforces construction hours from 7 a.m. to 7 p.m. On tight historic-area lots, starting early or working late can trigger neighbor complaints and stop-work orders. We schedule within those hours and communicate with adjacent homeowners before work starts.
Pricing for ADU Builders in Ontario, CA
Here’s what Ontario homeowners should expect to budget, based on the projects we’ve priced across the city in the last two years:
- JADU garage conversion: $80,000 – $150,000
- Detached ADU, prefab or modular: $130,000 – $220,000
- Detached ADU, custom stick-built: $220,000 – $420,000
- Electrical panel upgrade (100 to 200 amps): $3,500 – $6,000
- Site work, foundation, and utility connections: $25,000 – $50,000, often included in the ranges above
What moves the number is lot size, access, panel condition, and whether your property sits in an overlay district that requires design review. We give you a written line-item quote before any work starts, and that number doesn’t change at the door. Call (831) 292-4191 to schedule your free estimate.
We Also Serve Cities Near Ontario
Our crews cover Ontario and the surrounding communities, including Montclair, Upland, Chino, and Mira Loma. Whether you’re in a mid-century neighborhood near the 10 or a newer HOA community off the 15, we’ll give you the same written price, the same arrival window, and the same 365-day guarantee. If you’re just outside Ontario, give us a call and we’ll confirm coverage.
Serving Ontario, CA - Our Local Coverage Area
We’re based in the Ontario area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU Builders in Ontario
No, a formal party-wall notice isn’t required for a garage conversion when the wall is shared with your own home, not a neighboring property. Ontario’s building department will need structural drawings for any wall or opening changes, and we prepare those as part of the permit package. If your attached garage wall touches a neighbor’s structure, which is rare on Ontario’s standard lots, we’ll handle the notice and documentation before work begins. Call (831) 292-4191 and we’ll check your specific lot.
Ontario follows California ADU law, which generally allows a 4-foot rear and side setback for detached ADUs, but overlay districts and specific zoning classifications around the historic downtown can add stricter review or larger setbacks. We pull your specific lot’s zoning and overlay status before we quote, so the design we show you is one that will actually pass. That upfront check is free.
Yes, in most cases. A two-story detached ADU is allowed on a 6,000 square foot lot in Ontario as long as the height stays within the city’s limits, typically 16 feet for detached units unless the lot is within a half-mile of transit, which allows up to 18 feet. The bigger constraint is often the HOA on east-side properties, which may restrict height. We check CC&Rs before promising a design. Call (831) 292-4191 for a lot-specific answer.
Many Ontario homes built before 1980 will need a panel upgrade from 100 to 200 amps before a JADU can pass electrical inspection, especially if the unit includes a kitchen, mini-split, and laundry. The upgrade typically costs $3,500 to $6,000 and adds two to three weeks to the schedule. We verify panel capacity at the first site visit and include any upgrade in the written quote, so it’s not a surprise change order later.
Ontario enforces construction hours from 7 a.m. to 7 p.m., Monday through Saturday. We schedule all loud work, deliveries, and crane lifts within those hours, and we coordinate with neighbors on tight lots to keep access open. The hours don’t extend the overall schedule in most cases; they just shape how we stage the day. If a stop-work order happens, it’s almost always because someone worked outside those hours, and that’s exactly what we don’t do.
Written by Russ Delmar, Owner at Lodgewick ADU Riverside, serving Ontario and the surrounding Inland Empire communities since 2010.
Get Your Written Price Before You Decide
You’re not ready to sign a contract. You’re ready to see real numbers on paper. That’s what we give you. Call (831) 292-4191 and we’ll schedule a free site visit in Ontario, walk your lot, check your panel, look at your zoning, and hand you a written line-item price. No pressure. No door-knocker tactics. Just a straight answer from a builder who works in Ontario every week.
