Fast, Reliable New Detached ADU Across San Bernardino
A new detached ADU in San Bernardino typically runs $185,000-$340,000 all-in, from permit set through final inspection, depending on whether you build custom, go modular, or install a prefab unit. Most projects take 8-14 months from signed contract to certificate of occupancy, with the permit phase consuming the first 3-5 months. We’re the San Bernardino team at Ellery ADU Studio Rialto, and our crews work the Inland Empire daily - dispatch and scheduling run from our Riverside-San Bernardino office, so we’re never crossing county lines to reach a site. Call (951) 476-1467 and a live person picks up, 24/7. No voicemail queue, no callback that doesn’t materialize.
Why Ellery ADU Studio Rialto Is San Bernardino’s Preferred New Detached ADU Company
We’ve designed, permitted, and built more than 900 ADUs since 2015, the year California’s ADU laws shifted, and a significant share of those sit on San Bernardino lots. Our reputation here rests on documentation: a written price before any work starts, a photo record from every site visit, and a 365-Day Done Right Promise backed in writing under The Haven Standard. San Bernardino homeowners aren’t impressed by how long we’ve been around; they’re impressed by the permit set we deliver and the clause that locks their price.
Response time to San Bernardino is same-day for initial site visits - we don’t need to cross metro areas because our crews already work the flatland neighborhoods and foothill-adjacent parcels. That matters when you’re coordinating a site survey around a tenant’s schedule or trying to hit a permit submission window before the city’s next fee adjustment.
Our license number appears on every page, every contract, and every permit set. Background-checked, uniformed crews. Verified, not just claimed.
Our New Detached ADU Services in San Bernardino
Custom Built ADU
Custom built ADUs in San Bernardino run $220,000-$340,000 all-in, drawings through final inspection. This is the route for homeowners on deep lots in the Westside or near downtown who want a 1-bedroom or 2-bedroom unit sized to the specific setback lines their block allows. We design the permit set in-house, build from that same set, and hold one contract so the designer can’t blame the builder and vice versa. On older San Bernardino homes, we always open up the electrical and plumbing first - the 100-amp panel and galvanized supply line that the city will flag before signing off on a second dwelling unit. We price that upgrade upfront, not as a surprise.
Prefab ADU Installation
Prefab ADU installation in San Bernardino typically runs $185,000-$260,000, depending on the manufacturer and the site prep required. We specify and coordinate prefab systems from Abodu, Cover, and Tuff Shed within the same single contract that covers design, permitting, and installation. San Bernardino’s alley-access lots and wide driveways make crane-set delivery straightforward on many flatland blocks, though foothill parcels may need grading or retaining walls that add to the site-prep line item. We survey for utility tie-ins before quoting - the 200-amp service upgrade and new supply line are priced in writing, not discovered later.
Modular ADU
Modular ADUs in San Bernardino range $195,000-$280,000, factory-built to California’s Title 24 energy code and transported in sections for on-site assembly. We work with modular brands including Dvele, Mighty Buildings, and Plant Prefab, and we handle the local permitting that factory sales teams often gloss over. San Bernardino’s building department requires fire-rated assemblies on foothill-adjacent parcels in Very High Fire Hazard Severity Zones - ember-resistant venting, ignition-resistant cladding - and we specify those upgrades in the initial permit set so the factory builds to the right standard the first time.
Studio ADU
Studio ADUs in San Bernardino run $185,000-$245,000, typically 350-450 square feet, and they’re the most common detached unit we permit in the older flatland neighborhoods. A studio makes sense for the rental market San Bernardino actually has: warehouse and logistics workers from the BNSF intermodal, San Bernardino International Airport cargo ops, and the I-10/I-215 distribution belt who need housing close to work but can’t touch coastal rents. We size HVAC for 108-115°F valley-floor summers and Santa Ana wind exposure, not for milder assumptions. A studio that tenants abandon in August is a failed investment.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Before
AfterTrusted Brands We Service in San Bernardino
We specify and coordinate prefab and modular systems from Tuff Shed, James Hardie, and Abodu, among others, and we stock common cladding, flashing, and hardware for San Bernardino projects at our Inland Empire warehouse. That means when a Santa Ana wind event damages siding during construction or a fire-assembly detail needs revising after plan check, we’re not waiting two weeks for a parts run from Los Angeles. Turnaround on most material issues is 24-48 hours. Every brand we work with is folded into the same single contract - design, permit, factory coordination, site prep, install - so your price is your price.
Common New Detached ADU Problems We See in San Bernardino Homes
- The mandatory 100-to-200-amp service upgrade. San Bernardino’s building department treats a detached ADU as a second dwelling unit, which means the 100-amp panel in nearly every post-WWII ranch home must be upgraded before permit sign-off. We price this baseline electrical cost into every quote, along with the aging galvanized supply line that usually needs replacement at the same time.
- HVAC sized for coastal assumptions. San Bernardino’s 108-115°F summers and Cajon Pass Santa Ana wind events will punish an under-spec’d mini-split. We calculate cooling load for the valley floor, not Orange County, and we specify tight envelope details that keep utility bills low enough for tenants to stay through August.
- Failed waterproofing on original rear slabs. Mid-century flatland homes often have detached garages or rear patios on slabs with no vapor barrier or failed waterproofing. We core-test before designing, and if the slab’s compromised, we price a replacement or stem-wall foundation in the initial contract - not after walls are framed and moisture damage appears.
- Fire-assembly gaps on foothill parcels. Properties near the San Bernardino Mountains fall in Very High Fire Hazard Severity Zones, requiring ember-resistant venting and ignition-resistant cladding that standard coastal specs don’t include. We identify the zone during site survey and build those assemblies into the permit set from day one.
Pricing for New Detached ADU in San Bernardino, CA
| ADU Type | Typical All-In Range | What’s Included |
|---|---|---|
| Studio ADU (custom) | $185,000 - $245,000 | Permit set, 200-amp upgrade, slab/foundation, shell, finish, final inspection |
| 1-Bedroom Custom ADU | $245,000 - $310,000 | Same, plus full kitchen, bath, separate HVAC zone |
| 2-Bedroom Custom ADU | $290,000 - $340,000 | Same, with larger footprint and dual-ducted system |
| Prefab/Modular Studio | $185,000 - $260,000 | Factory unit, transport, crane set, site prep, utility tie-in, finish |
| Modular 1-Bedroom | $220,000 - $280,000 | Same, with factory-built kitchen/bath modules |
These ranges assume the typical San Bernardino baseline: 200-amp electrical upgrade, galvanized supply line replacement, and standard site prep on a flatland lot with alley or driveway access. Foothill parcels with grading, retaining walls, or fire-assembly upgrades move toward the top of each range. Under Haven Standard Clause 1, every project is quoted with a written price before any work begins - the words “call for a quote” do not appear on this site because your quote is written, itemized, and signed. Call (951) 476-1467 for your free estimate.
We Also Serve Cities Near San Bernardino
Our New Detached ADU crews work across the Inland Empire, including Rialto, Redlands, Riverside, and Fontana. Each city has its own building department, fee schedule, and inspection rhythm, and we permit in all of them. Dispatch runs from our Riverside-San Bernardino office, so response times stay short across the metro.
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 - New Detached ADU in San Bernardino
San Bernardino’s baseline costs run higher because nearly every post-WWII ranch home needs a 100-to-200-amp electrical service upgrade and galvanized supply line replacement before the city will approve a second dwelling unit - work coastal cities often skip because their housing stock was built to later codes. Add fire-assembly requirements on foothill parcels and HVAC sized for 108-115°F summers, and the gap makes sense. Call (951) 476-1467 for an exact quote on your property - estimates are free.
It won’t if the inspection happens before the contract is signed and allowances are written in for what we find. On a deep-lot 1956 ranch off the Westside near downtown, our crew pulled the garage slab and opened the rear wall of the main house for the new panel run, and what we found was original 100-amp service, cloth-wrapped wiring, and a galvanized supply line weeping at the meter. We upgraded the main to 200 amps and replaced the bad line under a written change order the homeowner approved before we touched anything, then set the detached studio on the rear footings the alley access made easy to reach. Under Haven Standard Clause 5 (No Surprises), any additional work is priced and approved in writing before we proceed - no door-side upsells, no scope creep.
Yes, and these neighborhoods are often ideal for it. Older flatland blocks near downtown and on the Westside frequently have rear-alley access and deep backyards that meet California’s by-right lot-coverage limits with room to spare, especially on 7,000-10,000+ sq ft lots that are oversized by California standards. The limiting factor is usually the electrical service, not the space. Call (951) 476-1467 and we’ll survey for feasibility - estimates are free.
We specify HVAC systems calculated for 108-115°F valley-floor design temperatures and tight insulation assemblies that handle Cajon Pass Santa Ana wind events. A mini-split sized by coastal assumptions will fail in August, and tenants will leave. We also specify low-E windows and proper solar orientation on the lot to reduce cooling load. The goal is a unit that stays occupied year-round, not one that sits empty through the hottest months.
It matters for timeline, price, and what the existing structure can handle. A new custom build gives maximum flexibility on a deep lot with alley access. Modular speeds factory construction but requires precise site prep and crane access. A detached garage conversion can work if the slab and framing are sound, but in San Bernardino’s 1950s-1970s stock, we often find the garage slab has no vapor barrier or the framing won’t meet current code without extensive rebuild - at which point new construction is sometimes the better value. We assess this during the free site visit and give you a written comparison.
Ready to price your detached ADU? Call (951) 476-1467 to schedule your free estimate. A live person answers 24/7. You’ll receive a written, itemized quote before any work begins, a documented photo record on every visit, and the 365-Day Done Right Promise backed under The Haven Standard. We also offer a Free Second Opinion on any written estimate you already have in hand.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving San Bernardino since 2015.