Fast, Reliable ADU Builders Across San Bernardino
Adding an ADU in San Bernardino typically costs between $180,000 and $320,000 for a detached unit, with prefab installations running $150,000 to $240,000 depending on site conditions. Most projects in the city’s older neighborhoods take 6 to 10 months from permit to final inspection. The biggest variable isn’t the structure itself. It’s what we find when we open up a 1950s tract home and the code upgrades that triggers. Sunstone ADU Builders handles that process every week in San Bernardino, and we’ll walk you through what actually happens before you spend a dollar. Call (855) 949-1913 to schedule a free site assessment.
Why Sunstone ADU Builders Is San Bernardino’s Preferred ADU Builders Company
San Bernardino homeowners call us because we’re ADU specialists, not a general contractor squeezing backyard units between kitchen remodels. Nate Holloway built Sunstone ADU Builders around one job: accessory dwelling units. That focus means our permitting knowledge, design constraints, and financing conversations happen daily here, not occasionally. We know what the city’s planning department asks for on a detached unit in a 1950s tract, because we’ve filed those plans dozens of times.
We’re an authorized builder and installer for Abodu, Cover, and Dvele prefab ADUs, and we build traditional stick-frame units too. The recommendation you get is based on your San Bernardino lot, your budget, and your timeline, not what we happen to sell. When we say one contractor from foundation to rental-ready interior, that includes the kitchen and bathroom finishing. No calling a second company after the shell is up. No coordinating schedules between trades that don’t know each other.
Our San Bernardino customers consistently mention two things: the written allowances we build into every contract for code-triggered surprises, and the fact that our crews show up when scheduled. In older neighborhoods like the 92404 and 92405 ZIP codes, that predictability matters more than a slick sales pitch.
Backyard ADU in San Bernardino
A backyard ADU in San Bernardino is a detached dwelling unit built on the same lot as the primary home, usually between 400 and 1,200 square feet. For homeowners in the city’s post-WWII tract neighborhoods around Baseline Street and Del Rosa Avenue, this is the most popular path to rental income or multigenerational housing. The typical San Bernardino lot is generous enough for a detached unit, but the house itself often fights the project with outdated electrical service, shallow sewer lines, and framing that hasn’t been touched since Eisenhower was president. A backyard ADU in San Bernardino generally runs $180,000 to $320,000, with prefab models like Abodu or Cover landing closer to $150,000 to $240,000.
Detached Garage Conversions
Many San Bernardino homeowners already have a detached garage, and converting it into an ADU is often cheaper than building new because the foundation and framing exist. But in the 92404 ZIP code, we routinely find 60-amp panels feeding cloth-wrapped wiring, and galvanized supply lines that disintegrate when we touch the shutoff. Those upgrades add cost, but they’re predictable when a contractor actually inspects before quoting.
Rental-Ready Unit Builds
When the goal is rental income, we scope the ADU with the finishes tenants expect: a functional kitchen, a full bathroom, and a separate entrance with proper privacy screening. Our in-house kitchen and bathroom remodeling capability means the unit is move-in ready under one contract, not handed to another contractor midway through.
ADU Construction in San Bernardino
ADU construction in San Bernardino covers everything from excavation and foundation through framing, mechanical, electrical, plumbing, insulation, drywall, and interior finish. On a 1952 stucco tract house near Del Rosa Avenue in the 92404 ZIP, our crew opened the garage wall for a detached ADU and found cloth-wrapped wiring spliced into a 60-amp panel, plus galvanized supply lines that crumbled at the shutoff. We priced the panel upgrade to 200-amp service and a full re-pipe as written allowances in the contract, got the homeowner’s signed approval before touching either system, and still hit the original foundation pour date.
That’s how ADU construction in San Bernardino should work. The surprises get found during inspection, not after demolition starts. A full build generally runs $200,000 to $320,000 in the city, depending on site access, soil conditions, and what the existing house throws at you.
Fire-Resistant Siding and Assembly
San Bernardino sits at the base of the San Bernardino Mountains, and many properties fall within wildfire interface zones. We specify James Hardie fiber cement siding on our ADUs, a material that resists flame spread and moisture far better than vinyl or wood. For properties in the high-fire areas, the building department often requires fire-resistant sheathing behind the siding as well. We know those requirements before we file, so the permit package is right the first time.
Kitchen and Bath Finishing In-House
Once the structure is watertight, our own crews finish the kitchen and bathroom. That means the person who framed your ADU walls also installs the cabinetry. For San Bernardino homeowners, this eliminates the single most frustrating gap in the process: waiting for a different contractor to show up after the shell is done. ADU construction in San Bernardino through Sunstone means one company, start to finish.
Trusted Brands We Service in San Bernardino
We’re an authorized builder and installer for Abodu, Cover, and Dvele prefab ADUs, and we work with Boxabl and Plant Prefab units when the site calls for them. Because we install these brands regularly in San Bernardino, we keep familiar hardware, flashing details, and standard components available locally, which cuts lead time. You’ll hear a brand recommendation based on your lot dimensions, set-back constraints, and budget, not because we have inventory to move.
Common ADU Builders Problems We See in San Bernardino Homes
- 60-amp electrical service with cloth wiring. Homes built in the 1950s across 92404 and 92405 were never designed for a second dwelling unit with air conditioning. Most projects trigger a mandatory 200-amp panel upgrade before the city will sign off.
- Shallow or collapsed sewer laterals. Pre-1970 San Bernardino homes often have clay or cast-iron sewer lines that fail camera inspection under the load of a new ADU. Replacement before final sign-off is common.
- Fire-resistant construction requirements in high-fire zones. Properties near the mountain interface face mandatory fire-resistant sheathing, tempered windows, and vegetation clearance. We build these requirements into the permit package upfront.
- Stucco that hides framing failures. San Bernardino’s hot, dry climate bakes stucco exteriors, but the damage behind it, termite runs, dry rot, failed shear panels, only shows up when walls are opened. We inspect before quoting so the number you sign reflects the work you’ll actually need.
Pricing for ADU Builders in San Bernardino, CA
A detached ADU in San Bernardino runs $180,000 to $320,000 for a stick-built unit. Prefab installations from Abodu, Cover, or Dvele typically land between $150,000 and $240,000 including site prep, foundation, and utility connections. Garage conversions usually fall between $120,000 and $180,000. Kitchen and bath finishing is included in our quotes, not billed as a separate phase afterward. The three factors that move your number most: electrical service capacity on the existing house, sewer lateral condition, and whether the property sits in a high-fire zone. Call (855) 949-1913 for a free estimate with line-item pricing, no vague allowances.
Key takeaways for San Bernardino homeowners: budget for the 200-amp panel upgrade if your house predates 1970. Expect a sewer camera inspection before final permit sign-off. Written allowances are your protection against mid-build surprises.
We Also Serve Cities Near San Bernardino
Our ADU Builders team regularly works in Muscoy, Highland, Loma Linda, and Rialto. If you’re in any of these surrounding communities, the same inspection-first approach applies. For specific permitting and cost guidance in San Bernardino, see our ADU Builders in San Bernardino page. Call us at (855) 949-1913 and we’ll come out, pull the panel cover, and tell you what’s actually there.
Serving San Bernardino, CA — Our Local Coverage Area
We’re based in the San Bernardino 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 Bernardino
Your 1950s tract home was built with 60-amp electrical service, which is enough for the house’s original load but nowhere near what a modern ADU with air conditioning, a kitchen, and a laundry draws. California building codes require the panel to support the combined load of both dwellings. In San Bernardino’s 92404 and 92405 ZIP codes, we see 60-amp panels on nearly every pre-1970 home we open. The upgrade to 200-amp service runs roughly $3,500 to $6,500 depending on the distance from the meter to the panel. We write it into the contract as a line item, so it’s approved and priced before work begins. Call (855) 949-1913 for an exact number based on your house.
Cloth-wrapped wiring, galvanized supply lines that crumble at the fittings, and cast-iron drain pipes that have corroded to the width of a pencil. On one 1952 stucco off Del Rosa Avenue, the galvanized supply line snapped when our plumber touched the shutoff valve. That’s not a defect in the house; it’s just age. San Bernardino’s hot, dry climate doesn’t damage pipes the way freeze-thaw cycles do, but galvanized steel rusts from the inside out regardless. We inspect these systems before quoting so the price you sign reflects what’s actually behind your walls.
It often does. Many pre-1970 San Bernardino homes have shallow clay sewer laterals that were never designed for a second bathroom and kitchen. When we camera the line, which happens on every garage conversion we quote, we routinely find bellies, root intrusion, or collapsed sections. The city requires the lateral to be in functional condition before final sign-off on a new dwelling unit. If replacement is needed, that’s another $8,000 to $15,000 depending on length and depth. Better to know that before the permit is filed than after the drywall is up. Call (855) 949-1913 and we’ll camera your line as part of the free estimate.
Properties in the wildfire interface zones along the mountain base require fire-resistant construction materials and assemblies. That typically means fire-rated sheathing, tempered glass, ember-resistant vents, and a Class A roof assembly. We specify James Hardie fiber cement siding on every ADU we build in San Bernardino, which meets the fire-resistance requirements and holds up to the semi-arid heat better than vinyl or wood. The city’s building department checks these details at plan review, and if they’re not in the drawings, you lose weeks on resubmittal. We file these details correctly the first time, which is part of why our ADU permits move through San Bernardino’s planning desk without drama.
Yes, and for many San Bernardino properties, prefab is the faster path. Abodu, Cover, and Dvele units are approved for California ADU use and we’re an authorized installer for all three. Boxabl works on lots with sufficient crane access and a foundation designed for its specific load points. The catch on older San Bernardino lots is always the same: the existing house’s electrical service, sewer lateral, and any high-fire zone requirements still apply regardless of whether the ADU arrives on a truck or gets framed on site. We evaluate the site first, then tell you which construction method makes sense. Call (855) 949-1913 and we’ll walk your lot and give you a straight answer.
Written by Nate Holloway, Owner at Sunstone ADU Builders, serving San Bernardino and the Inland Empire. Nate leads every site assessment in the San Bernardino area and personally reviews every contract before it goes to the homeowner.