Fast, Reliable New Detached ADU Across San Bernardino
A new detached ADU in San Bernardino typically runs $220,000-$380,000 all-in, from the first site measurement through final inspection, depending on whether you’re building from slab up or specifying a prefab system like Abodu or Cover. We’re Ellery ADU Studio, a design-build practice that handles the drawings, permit set, and construction under one contract at one written price - no designer-versus-builder blame gap when something doesn’t line up. Our crews serve San Bernardino from our Inland Empire office; call (951) 379-3047 and a live person picks up, 24 hours a day.
Why Ellery ADU Studio Moreno Valley Is San Bernardino’s Preferred New Detached ADU Company
We’ve designed, permitted, and built over 900 ADUs since 2015, the year California’s ADU laws shifted, and a growing share of those have been in San Bernardino’s post-WWII flatland neighborhoods. San Bernardino homeowners find us because they’ve already read the three-star reviews elsewhere and want the permit set treated as the core product, not an afterthought.
Our response time to San Bernardino is same-day for initial site visits, scheduled from our Inland Empire office. We know the local terrain: the 1950s-1970s tract homes on 7,000-10,000 sq ft lots, the slab-on-grade garages along the Route 66 corridor, the raised wood-frame foundations on east-side streets, and the foothill parcels north of Highland Avenue where CAL FIRE rules kick in. That local fluency means fewer surprises in the permit set and fewer change orders once construction starts.
Every project is governed by The Haven Standard. Clause 1 locks a written price before any work begins. Clause 5 locks the scope at signing - no door-side upsells. And our 365-Day Done Right Promise means if the finished ADU isn’t built to the permitted drawings, we make it right, in writing, before the first nail.
Our New Detached ADU Services in San Bernardino
Custom Built ADU
Custom built ADUs in San Bernardino start around $280,000 and run to $380,000+ for a 2-bed unit with full kitchen and laundry. We design to your lot’s specific constraints - setback variances, utility trenching across a deep San Bernardino backyard, or matching the roofline of a 1964 ranch house in the Del Rosa neighborhood. The permit set includes structural calcs for the local seismic zone, since the San Andreas Fault runs along the city’s northern mountain boundary and the city requires that evaluation before square footage is added.
Prefab ADU Installation
Prefab ADU installation in San Bernardino typically ranges $220,000-$320,000, depending on the manufacturer and site prep required. We specify and coordinate Abodu, Cover, and Dvele systems within the same single contract - you don’t manage the prefab vendor and the local builder separately. In San Bernardino’s heat, we oversize the mini-split specification compared to coastal installs; a unit rated for Long Beach will not hold temperature in a 108°F August afternoon on the valley floor.
Modular ADU
Modular ADUs in San Bernardino fall in the $240,000-$340,000 range, delivered in sections and set on a permanent foundation we prep and pour. The advantage here is factory precision on the building envelope, which matters in San Bernardino where Santa Ana winds through the Cajon Pass test every flashing detail. We handle the transport permits, crane coordination, and the local inspection sequence that ties the modular sections to your utility connections.
Studio ADU
Studio ADUs in San Bernardino - typically 350-450 sq ft - run $180,000-$260,000. These are popular with homeowners in the Arrowhead and Pacific neighborhoods who want rental income without maxing out their lot coverage. We design the kitchenette and bath layout to the California Building Code’s efficiency standards, and we specify the HVAC for the inland valley’s actual temperature extremes, not the milder coastal assumptions.
1-Bed & 2-Bed ADU
1-bed detached ADUs in San Bernardino typically run $220,000-$300,000; 2-bed units run $280,000-$380,000. The bedroom count drives the septic or sewer connection sizing, the electrical service upgrade, and the parking waiver math under San Bernardino’s local ADU ordinance. We’ve navigated those calculations on dozens of San Bernardino permits, and the drawings reflect what the city planner will actually see when the set hits their desk.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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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.
Trusted Brands We Service in San Bernardino
We specify and coordinate prefab and modular systems from Abodu, Cover, Mighty Buildings, and other manufacturers, integrating them into the same single-contract workflow as our stick-built projects. For San Bernardino homeowners, this means the brand’s engineering talks directly to our permit set - no gap between the factory drawings and what the city inspector reviews. We also specify James Hardie siding on many custom builds for its fire-resistant properties, particularly relevant on foothill parcels where CAL FIRE standards apply.
Common New Detached ADU Problems We See in San Bernardino Homes
- Outdated wiring behind intact drywall. On east-side streets off the Route 66 corridor, we regularly find cloth-wrapped knob-and-tube-era wiring in 1960s garages that looks fine until the walls open. Our contracts include an electrical allowance with a written trigger price, so the upgrade to modern Romex and panel capacity is approved before we touch a stud.
- Failed waterproofing on slab-on-grade foundations. San Bernardino’s older garages often have stem walls with failed membrane or no membrane at all. Water-stained framing at the slab edge is common. We sister damaged members, re-flash, and re-roof with a Class A assembly where required - all priced in writing before demolition.
- HVAC undersized for inland valley heat. A mini-split spec’d for coastal California will not cool a San Bernardino ADU in August. We size for 108-112°F design temperatures and specify higher-SEER equipment with sufficient BTU overhead for the actual thermal load.
- Santa Ana wind damage to roof attachments. The Cajon Pass and San Gorgonio Pass corridors funnel intense wind events through the city. We engineer roof attachment and flashing details to withstand those loads, not just the baseline code minimum.
Pricing for New Detached ADU in San Bernardino, CA
| ADU Type | Typical Range (San Bernardino) | What Drives the Top of Range |
|---|---|---|
| Studio ADU (custom) | $180,000-$260,000 | Utility trenching, septic upgrade, CAL FIRE zone |
| 1-Bed ADU (custom) | $220,000-$300,000 | Foundation type, electrical service upgrade |
| 2-Bed ADU (custom) | $280,000-$380,000 | Full kitchen, laundry, sewer/septic capacity |
| Prefab ADU (installed) | $220,000-$320,000 | Manufacturer, site prep, crane access |
| Modular ADU (installed) | $240,000-$340,000 | Transport permits, foundation, utility tie-in |
These ranges are all-in: drawings, permit set, construction, final inspection. Under Haven Standard Clause 1, the written price is locked before any work begins. If your walls reveal problems we couldn’t see - and on San Bernardino’s 1950s-1970s stock, they often do - the allowance triggers are already in the contract, with upgrade prices approved in writing before we proceed. No surprise invoices, no scope creep. Call (951) 379-3047 for your free estimate.
We Also Serve Cities Near San Bernardino
Our crews work throughout the Inland Empire, including San Bernardino and neighboring Highland, Rialto, Colton, and Grand Terrace. Each city has its own ADU ordinance nuances, and our permit sets reflect those differences. If you’re on the border between jurisdictions, we’ll tell you which rules apply to your specific parcel before we draw a single line.
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
Cloth-wrapped wiring, water-damaged framing at the slab edge, and failed waterproofing are the three most common finds in San Bernardino’s 1950s-1970s garage stock. On an east-side street off Route 66, our crew opened a 1962 detached two-car garage and found all three - knob-and-tube-era wiring, stained slab-on-grade framing, and a membrane that had failed years earlier. We had flagged exactly this scenario in the contract with a written allowance; the homeowner approved the electrical, framing, and roofing upgrades before we touched another stud. Call (951) 379-3047 for a free estimate - we’ll walk your specific garage and tell you what we expect to find.
We build inspection-first allowances into every contract, with trigger prices written in plain English before signing. Under Haven Standard Clause 5 (No Surprises), if the walls reveal wiring, framing, or foundation problems, we stop work, document with photos, and present the exact upgrade cost for written approval before proceeding. The homeowner on that east-side Route 66 project knew the electrical upgrade would run $4,200-$6,800 if needed, because it was right there in the contract. No door-side upsells. Call (951) 379-3047 to schedule your free estimate.
Only if your parcel falls within a California-designated Very High Fire Hazard Severity Zone, which in San Bernardino means most foothill properties north of Highland Avenue bordering the San Bernardino National Forest. If CAL FIRE standards apply, your detached ADU requires Class A roofing, ember-resistant vents, and one-hour fire-rated exterior assemblies - adding $15,000-$25,000 to the same build a mile south on the flatlands. We check your parcel’s fire hazard designation in the preliminary site review and price accordingly in the written quote. Call (951) 379-3047 to confirm your status.
Substantially oversized compared to coastal Southern California. San Bernardino’s inland valley traps heat, with summer afternoons regularly hitting 108-112°F. A mini-split that handles a similar unit in Long Beach will struggle to maintain setpoint here, especially in a detached garage conversion with poor existing insulation. We size for the actual design temperature and specify higher-SEER equipment with BTU headroom. For a typical 450 sq ft studio ADU, that usually means a 12,000-18,000 BTU system rather than the 9,000-12,000 coastal standard. Call (951) 379-3047 for an exact load calculation on your project.
Yes. Because the San Andreas Fault runs along San Bernardino’s northern mountain boundary, the city requires a seismic evaluation before adding square footage to any structure, including a new detached ADU. On slab-on-grade or raised wood-frame foundations common in the 1945-1975 housing stock, this evaluation determines whether the existing foundation can support the new load or needs reinforcement. We include this assessment in our preliminary site visit and reflect any required upgrades in the written quote. Call (951) 379-3047 to schedule your free estimate.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving San Bernardino since 2015.