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 San Dimas
Adding an ADU in San Dimas usually costs between $180,000 and $420,000 for a detached unit, with garage conversions starting around $120,000. The final number depends on slope, access, and how much site work your particular lot needs. If you’re on a hillside parcel off Foothill Boulevard or tucked into a cul-de-sac near Lone Hill Avenue, grading and drainage can shift the budget before a single wall goes up. We scope it all in writing before you sign anything. Call (903) 568-7222 to schedule a free estimate with Troy Eastman and our San Dimas team.
Why Benson ADU Builders Is San Dimas’s Preferred ADU Builders Company
San Dimas homeowners keep calling us for one reason: we put the full plan and the full price on paper before work starts. That matters here more than in flatter cities, because a San Dimas lot rarely behaves like a clean, level rectangle. Sloped rear yards, easement questions, and LA County Fire review requirements show up on a meaningful share of the ADU projects we quote in this city. When they do, the contractor who gave a verbal estimate starts adding change orders. Ours doesn’t.
Every project carries our 365-Day Done Right Promise. If something isn’t right within a full year, we come back and make it right, in writing. That guarantee has been on every project since Benson ADU Builders joined the Relay Home Co. family, which was founded in 2006. Troy Eastman leads our team with the same standard on every San Dimas job: background-checked, uniformed technicians, a live person answering the phone around the clock, and a written guarantee at the end.
We’re not a general contractor who occasionally builds an ADU. Our ADU Builders team does this every day, with access to Abodu, Cover, Dvele, and Mighty Buildings panelized shells and James Hardie cladding. You can research every brand we carry before you ever talk to us. That’s the point.
ADU Plans in San Dimas
ADU Plans in San Dimas are the architectural and site drawings that LA County and the City of San Dimas require before any permit gets issued, and they’re where a foothill lot either gets scoped properly or gets underestimated. On a flat parcel, a standard ADU plan set runs $6,000 to $12,000. On a sloped lot behind an existing single-story home in the hillside corridor, expect $10,000 to $18,000 once you factor in grading notes, drainage details, and any review comments from planning.
What the plan set actually covers
Your ADU Plans need a site plan showing setbacks from property lines and the main house, a floor plan, elevations, structural details for the foundation and roof, and electrical and plumbing layouts. If your San Dimas parcel sits on a slope, the plan set also has to show how water moves away from both the new unit and the neighbor’s wall. That drainage sheet is not optional. LA County Fire will look at it during review.
When San Dimas homeowners need plan help
You need drawings before any legitimate contractor can give you a fixed price. We handle this in-house, because a plan set done without local site knowledge produces a bid that falls apart the first week of grading. We’ve seen homeowners pay for plans that assumed a flat pad, only to discover their rear yard drops four feet in thirty. That’s a redesign, a re-review, and a delay. We draw it right the first time because we’ve built on these lots.
ADU Contractor in San Dimas
An ADU Contractor in San Dimas is the licensed builder who takes the plans, pulls permits, and manages every trade from foundation through final inspection, and on a foothill lot that role is more about site work than about framing. A typical detached ADU build in San Dimas runs $180,000 to $420,000 depending on size, finish level, and what the ground does. Garage conversions run less, $120,000 to $180,000, because the shell already exists. The site work is where San Dimas contractors either earn their fee or hide their mistakes.
What site work really costs here
Grading a sloped San Dimas rear yard for a 600 sq ft unit usually runs $8,000 to $25,000 before concrete. Utility trenching from the main house to the ADU, including sewer, water, and electrical, typically adds $10,000 to $20,000 depending on distance and whether you’re crossing a driveway. If your lot has a shared easement or the hillside pushes you into a retaining wall, add $15,000 to $40,000. These are real San Dimas numbers, not national averages.
How we keep the price from moving
The price moves when the original estimate ignored the slope. We prevent that by walking every San Dimas parcel with a level and a tape before we quote. Troy Eastman reviews every plan set against the actual site, not just the drawings. When we hand you a written price, the grading, drainage, utilities, and panel set are already in it. That’s what a fixed price means.
Trusted Brands We Service in San Dimas
We build with Abodu, Cover, Dvele, and Mighty Buildings prefab shells, and we finish exteriors with James Hardie cladding. For San Dimas customers, we keep the conversations practical: a Mighty Buildings panelized shell goes up fast and handles our dry foothill heat well, while James Hardie siding stands up to the sun on the south-facing slopes better than wood products. We’re factory-authorized to install these systems, which means you get a real warranty from the manufacturer plus our 365-Day Done Right Promise. No gray-market kits, no off-brand substitutions.
Common ADU Builders Problems We See in San Dimas Homes
- Existing slabs that won’t pass current code. A garage conversion quote assumes the old slab is thick enough and has proper footings. In San Dimas homes built from the 1950s through the 1980s, that’s frequently not true. We check before we quote, not after demo.
- Drainage that pushes water toward the neighbor’s wall. On sloped lots near the foothills, a poorly planned ADU sends runoff into the property next door. City planning and LA County Fire will flag this during review. We design the grading away from every adjacent structure from day one.
- Prefab quotes that skip the site work. A Boxabl or Cover shell price is not an all-in price. The pad, the trenching, the connections, and the ADU Plans are still required in San Dimas before that shell gets set. We quote the whole scope, not just the product.
- Setbacks that surprise homeowners late. San Dimas hillside parcels often have side and rear setback requirements that differ from flat-grid rules. A plan drawn without checking the parcel’s slope designation gets redlined at planning review. We’ve handled enough of these to know what flies before we submit.
Pricing for ADU Builders in San Dimas, CA
Here’s the honest math for San Dimas. A detached ADU with basic finishes runs $180,000 to $320,000 on a relatively flat parcel. The same build on a sloped lot with retaining walls and a long utility run lands at $300,000 to $420,000. Garage conversions run $120,000 to $180,000 assuming the slab passes, and $180,000 to $230,000 if the foundation needs re-pouring. Junior ADUs inside the existing footprint cost $85,000 to $150,000. All of these include plans, permits, site work, and our written guarantee. Call (903) 568-7222 and we’ll give you a line-item quote for your specific lot, not a national range.
We Also Serve Cities Near San Dimas
Benson ADU Builders works throughout the San Gabriel Valley. If you’re in San Dimas, we’re your local crew. We also serve La Verne, Glendora, Covina, and Azusa with the same written-price guarantee and the same 365-Day Done Right Promise on every project. Wherever your lot is, the process starts the same way: a free on-site walk, a written scope, and a fixed price before anything gets signed.
Serving San Dimas, CA - Our Local Coverage Area
We’re based in the San Dimas 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 San Dimas
An ADU builder specializes in the full scope of a second unit: plans, setback review, grading, foundation, utility connections, prefab or site-built construction, and the final inspection. A general contractor might do one ADU every few years. We do them weekly, and in San Dimas that means we’ve already solved the slope, drainage, and fire review problems that a generalist encounters for the first time on your lot. Call (903) 568-7222 for a free estimate.
No, not before you get a ballpark. We can walk your lot, check the slope and access, and give you a written price range on the spot. The formal ADU Plans come next, and we draw them in-house after the walk. A final fixed price follows the plan set. What you should not do is pay for plans from a designer who’s never built on a San Dimas hillside. Start with the site walk. It’s free.
A detached ADU in San Dimas typically takes 7 to 12 months from first walk to final inspection. Plan drawing and city review run 2 to 4 months depending on whether your lot triggers a hillside review comment. Construction runs 4 to 8 months. Prefab shells like Mighty Buildings or Abodu can cut framing time by several weeks, but the grading, trenching, and inspections don’t speed up. We’ll give you a written schedule with your fixed price, and we update it in real time through the build.
We’re authorized to build with Abodu, Cover, Dvele, and Mighty Buildings. Each has strengths, and we’ll tell you which one fits your San Dimas lot honestly. A tight rear-yard access off Cataract Avenue might favor a panelized Mighty Buildings system. A flatter lot with open truck access can handle a wider prefab module. We’ll show you the options and let you research every brand yourself before you choose.
The price only changes if the scope changes, and the scope changes when the original estimate ignored something real: a slab that fails, a slope that needs a wall, a utility line that has to cross a neighbor’s easement. We prevent those surprises by checking all of it during the free site walk. The written price we hand you includes the grading, drainage, utilities, plans, and permits for your specific parcel. If you want to add square footage or upgrade finishes mid-build, that changes the price. Otherwise the number holds. Call (903) 568-7222 and we’ll put it in writing.
How We Build on San Dimas Slopes
San Dimas is a small, largely built-out foothill city, and nearly every ADU lot sits inside the San Gabriel Valley’s hillside and Foothill Boulevard corridor. That means most projects are garage conversions or backyard infill behind existing single-story homes rather than large new-footprint builds. Grading, drainage, and setback review through LA County Fire and city planning usually drive the scope more than the structure itself. We bid that reality from the first visit.
We built a detached 600 sq ft ADU on a lot off Cataract Avenue backing up toward the foothills, converting a failing rear slab and adding a James Hardie-clad unit with a Mighty Buildings panelized shell. Our crew had to work around the property’s slope and a shared driveway easement, so we re-poured the pad, re-graded the drainage away from the neighbor’s wall, and pulled the ADU plans through San Dimas planning with a hillside review comment. The final unit cleared framing and final inspection without a change order because we scoped the grading, utility trenching, and panel set before signing.
That’s the difference between a contractor who knows San Dimas and one who’s driving in from somewhere flat. If your lot slopes, your builder should know it before you pay for plans. We do.
Get Your San Dimas ADU Price in Writing
You should know the ballpark before you ever tap “call.” We’ll walk your San Dimas lot, check the slope and access, and hand you a written price with a written schedule. No verbal estimates that drift later, no change orders that appear after demo. Just a real plan and a real price, backed by a 365-Day Done Right Promise. Call (903) 568-7222 to schedule your free estimate with Troy Eastman and the Benson ADU Builders team.
Written by Troy Eastman, Owner at Benson ADU Builders, serving San Dimas homeowners with fixed-price ADU construction and prefab installation.
