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 or go prefab. Most San Bernardino homeowners see plan check approval in 8-14 weeks and construction in 4-7 months after that. Call (909) 359-6463 to schedule your free estimate - we’ll bring a written price, not a callback promise.
We’ve designed, permitted, and built ADUs across San Bernardino since 2015, from the post-war tracts near Del Rosa to the spacious lots backing onto alleys in the Verdemont hills. Our crews are dispatched from the Inland Empire office and serve San Bernardino locally. We know the building department’s plan check rhythms, which neighborhoods trigger fault-proximity reviews, and why a detached ADU here needs a different material spec than one in Riverside or Ontario.
Why Ellery ADU Studio San Bernardino Is San Bernardino’s Preferred New Detached ADU Company
Our reputation in San Bernardino is built on documented outcomes, not marketing claims. We’ve completed 900+ ADUs across California since 2015, and a significant share sit on San Bernardino lots where the San Andreas Fault trace runs close enough to matter. San Bernardino homeowners review us consistently on the specifics: the written price held, the permit set was complete the first time, the photo record showed what happened on every visit.
Response time to San Bernardino inquiries is same-day during business hours - a live person answers calls 24/7, no voicemail queue. For existing clients in San Bernardino, our documented photo record means you see what we found, not what we felt, on every site visit.
Local knowledge that changes outcomes: we know which San Bernardino neighborhood plans require a geotechnical engineer’s soils report before foundation permit issuance, and we flag that in the first meeting - not after plan check kicks your drawings back. That difference alone has saved San Bernardino clients six to ten weeks on projects in Verdemont and near the Highland border.
Our New Detached ADU Services in San Bernardino
Custom Built ADU
Custom detached ADUs in San Bernardino start around $220,000 and run to $340,000+ for larger 2-bedroom units with upgraded finishes. We design the permit set in-house, build from that same set, and warranty the result under one contract at one written price. On a recent project off North E Street near the 210, we specified hot-dip galvanized post bases and stainless roofing fasteners after the homeowner’s previous electro-galvanized hardware failed within four seasons of San Bernardino’s temperature swings and occasional hard freezes. The Haven Standard, Clause 1, locks your written price at signing - no door-side upsells, no scope creep.
Prefab ADU Installation
Prefab detached ADUs in San Bernardino typically range $185,000-$280,000 all-in, including site prep, foundation, utility tie-ins, and permit fees. We specify and coordinate systems from Cover, Dvele, and Mighty Buildings within our single-contract model - the factory build happens parallel to your foundation and utility work, compressing overall timeline. San Bernardino’s alley-access lots and rear-yard setbacks on 7,500-10,000 sq ft parcels make prefab delivery and crane placement straightforward on most sites. We handle the geotechnical report if your lot falls in a fault-proximity study zone, and we spec the foundation to match - not the generic slab the prefab vendor’s standard drawing assumes.
Modular ADU
Modular detached ADUs in San Bernardino run $195,000-$295,000 complete, with the module manufactured off-site while we prepare your foundation and utilities. The advantage is factory precision on a timeline that doesn’t expose framing to San Bernardino’s 108°F summer highs or hard freeze events. We coordinate modular delivery with crane access, utility rough-in, and final tie-down to California’s seismic standards - critical here, where the San Andreas proximity means anchorage and lateral bracing get extra scrutiny at inspection.
Studio ADU & 1-Bed & 2-Bed ADU
Studio detached ADUs in San Bernardino typically cost $185,000-$240,000; 1-bedroom units run $210,000-$290,000; 2-bedroom units run $250,000-$340,000. These ranges include the full design-build scope, permit set, city fees, and documented photo record on every visit. On a 1-bed unit we set on a rear-alley lot off Verdemont Road in Verdemont, the soils report flagged fault-proximity conditions, so we specced freeze-protected exterior supply lines and stainless fasteners after the homeowner’s previous fence posts rotted out at the base. We upgraded their 100-amp panel to carry the ADU load and used James Hardie siding on marine-grade-coated framing hardware instead of the builder-grade galvanized the first quote listed. That ADU passed inspection on the first try. The cheap inland spec would have cost less at signing and more within a decade.
What happens when you call
- 1
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 Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie - all within our single-contract, one-written-price model. For San Bernardino’s climate and seismic exposure, we default to marine-grade-coated hardware and stainless fasteners on any brand’s standard spec that ships with electro-galvanized. James Hardie fiber-cement siding is our standard recommendation here over wood-based products - it handles the 108°F to hard-freeze swing without the swelling and fastener pop we see on standard lap siding within five years. Local parts and material procurement are coordinated through our Inland Empire supply chain, so replacement or add-on orders don’t wait on out-of-region shipping.
Common New Detached ADU Problems We See in San Bernardino Homes
- Going with the cheap inland spec. Electro-galvanized fasteners, standard window frames, unsealed paver joints - hardware rusts and wood swells within a few seasons even though San Bernardino is inland. The temperature swings and occasional hard freezes accelerate corrosion faster than coastal builders expect. We spec hot-dip or stainless hardware and sealed joints from the start.
- Ignoring the fault-proximity study zone in northern neighborhoods. Parcels near Verdemont and the Highland border can trigger a required geotechnical report before foundation permit issuance. Most Inland Empire ADU contractors never mention this, and clients lose weeks when plan check kicks the drawings back. We identify this risk in the first meeting and include the report in timeline and budget.
- Sizing ADU HVAC and exterior plumbing to coastal Inland Empire norms. San Bernardino’s inland valley location at 1,050 ft elevation sees summer highs past 108°F and hard freezes that Riverside and Ontario don’t match. An undersized mini-split can’t hold setpoint; unprotected exterior supply lines freeze. We spec higher-BTU HVAC with wider operating ranges and freeze-protected plumbing on every detached ADU.
- Leaving the existing 60-100 amp panel in place. San Bernardino’s 1950s-1970s housing stock almost always has original panels at 60-100 amps. Adding a detached ADU load almost always triggers a service upgrade requirement mid-permit, killing timeline and adding $3,500-$6,500 in unplanned cost. We test and spec the electrical upgrade in our initial scope - it’s in your written price from day one.
Pricing for New Detached ADU in San Bernardino, CA
New detached ADU pricing in San Bernardino breaks down as follows:
| ADU Type | Typical Range (All-In) |
|---|---|
| Studio ADU (custom) | $185,000 - $240,000 |
| 1-Bedroom ADU (custom) | $210,000 - $290,000 |
| 2-Bedroom ADU (custom) | $250,000 - $340,000 |
| Prefab/Modular ADU (installed) | $185,000 - $295,000 |
| Geotechnical report (if triggered) | $2,800 - $5,500 |
| Electrical service upgrade | $3,500 - $6,500 |
What moves you within these ranges: size, finish level, and whether your lot triggers fault-proximity requirements. The geotechnical report is not optional when the building department requires it - we identify that risk upfront and include it in your written price if applicable. Every project is quoted with a written price before any work begins, per Haven Standard Clause 1. Call (909) 359-6463 for your exact number - estimates are free, and we offer a Free Second Opinion on any written estimate already in hand.
We Also Serve Cities Near San Bernardino
Our New Detached ADU in San Bernardino crews also work in Highland, Rialto, Colton, and Grand Terrace - same single-contract model, same written-price guarantee, same documented photo record on every visit. Each city has its own plan check quirks and soil conditions; we adjust the spec accordingly rather than copy-paste the San Bernardino approach.
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
If your property sits in a fault-proximity study zone - common in northern San Bernardino neighborhoods like Verdemont and near the Highland border - the building department will require a licensed geotechnical engineer’s report before issuing your ADU foundation permit. Not all San Bernardino lots trigger this; we check your parcel against the state Alquist-Priolo maps in our first meeting and tell you before you sign. Call (909) 359-6463 and we’ll confirm whether your specific address is affected - estimates are free.
San Bernardino’s inland valley climate creates wider temperature swings and more corrosion stress than coastal builders assume - summer highs past 108°F expand and contract fasteners, while hard freezes condense moisture into gaps. Electro-galvanized hardware that survives ten years near the beach fails in four to six here. We spec hot-dip galvanized or stainless fasteners and marine-grade-coated framing hardware as standard on every San Bernardino detached ADU. Call (909) 359-6463 for a written quote that shows exactly what hardware your project gets.
Almost never. San Bernardino’s post-WWII housing stock was built with 60-100 amp service that barely supports modern baseline loads. Adding a detached ADU’s kitchen, HVAC, and water heater will trigger a service upgrade requirement at plan check or inspection. We test your existing panel and spec the upgrade in your initial written price - not as a surprise change order mid-project. Call (909) 359-6463 and we’ll assess your electrical capacity during the free estimate.
San Bernardino’s 1,050 ft elevation and inland location produce summer highs past 108°F and hard freezes that coastal Inland Empire cities don’t match. Your HVAC needs higher BTU capacity with a wider operating range; your exterior plumbing needs freeze-protected supply lines and buried depth below the frost line. We size systems to San Bernardino’s actual conditions, not Riverside’s. Call (909) 359-6463 for a written spec that matches your lot’s climate exposure.
Yes - San Bernardino’s rear alleys and spacious lots make detached garage-to-ADU conversions one of the most common projects we handle here. The existing slab is often usable, though we test thickness and reinforcement; the electrical panel almost always needs upgrade; and if your garage sits in a fault-proximity zone, the foundation work may still trigger geotechnical review. Our New Detached ADU team handles both new construction and garage conversion ADUs under the same single contract at one written price. Call (909) 359-6463 to compare new-build versus conversion costs for your specific property.
Ready to price your project? Call (909) 359-6463 to schedule your free estimate. You’ll receive a written price before any work starts, a documented photo record on every visit, and the 365-Day Done Right Promise - all backed by The Haven Standard in writing.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving San Bernardino since 2015.