Fast, Reliable ADU Builders Across San Bernardino
Adding an ADU to a San Bernardino home usually means working with buildings from the 1940s through the 1970s, and that changes the whole job. We know these houses: the stucco ranches off Del Rosa Avenue, the long lots with detached garages down toward 92411, the postwar neighborhoods where a backyard casita has been there since before anyone kept records. That local knowledge is why our estimate for your San Bernardino ADU will actually hold up when our crew opens the walls. Call (877) 658-7475 to schedule a free estimate with Nolan Treffert and the Casita ADU Builders team.
Why Casita ADU Builders Is San Bernardino’s Preferred ADU Builders Company
Casita ADU Builders does one thing: accessory dwelling units. We do not run a general contracting operation on the side, and we do not take work outside the ADU space. That narrow focus means every process we run in San Bernardino, from the first lot assessment to the final inspection, exists specifically for this building type. Nolan Treffert leads the team with a clear operating rule for older San Bernardino homes: inspect first, price honestly, and never let a homeowner find out about a five-figure code upgrade after demo is done.
We work across all the leading prefab brands so you choose the right ADU, not just the one we happen to sell. That matters in San Bernardino, where the city’s updated ADU ordinance allows up to two units on a single-family lot. Some lots suit a compact prefab from Abodu or Cover, delivered and set in weeks. Others need a custom ADU Builders approach because the existing structure is a 60-year-old garage with cloth wiring and a cracked slab. We match the build type to your lot, not the reverse.
San Bernardino homeowners work with us because we show up expecting what these older homes actually contain. A garage conversion in the 92410 area near Highland Avenue will look different from one in a newer Rialto subdivision a few miles west, and we plan for that difference before quoting. Our estimates for San Bernardino projects include written allowances for the code upgrades these homes typically require, so the price you approve is the price you pay, unless you approve a change in writing first.
ADU Construction in San Bernardino
ADU Construction in San Bernardino means building a legal, permitted dwelling unit on a lot where the house was probably built before the current electrical code existed. The job involves foundation work, framing or prefab installation, electrical and plumbing upgrades, insulation rated for San Bernardino’s 100-degree summers, and a finished interior. A full custom ADU construction project in San Bernardino typically runs $180,000 to $320,000 depending on size, foundation conditions, and whether the existing garage or backyard structure gets reused or demolished. Prefab ADU construction, using a factory-built unit from Abodu or Cover, typically runs $150,000 to $250,000 including site work and utilities; if you need Cover repair in San Bernardino, we handle that as part of the site scope.
What Older San Bernardino Homes Require
Homes built in San Bernardino between the 1940s and 1970s frequently have undersized electrical panels, ungrounded wiring, and foundations that were poured before modern seismic standards. When an ADU gets added, the permit triggers a review of the existing house’s service panel capacity. We inspect the panel, the wiring path, and the foundation before quoting so those upgrades appear in the estimate, not as a surprise later.
San Bernardino Permit Path
The city’s ADU ordinance now allows both an attached and a detached unit on single-family lots. Our ADU Builders in San Bernardino team handles the full permit package: site plan, structural drawings, energy calculations for the Title 24 requirements, and the inspections through to final sign-off. We pull the permits, and we stay on the job until the city passes it.
Detached ADU in San Bernardino
A Detached ADU in San Bernardino is the most common project we design, because so many lots here have rear garages with alley access that can be converted or replaced without touching the main house. A new detached ADU in San Bernardino typically runs $130,000 to $260,000 for a one-bedroom unit with a kitchenette and full bath. A garage conversion into a detached ADU runs $110,000 to $210,000, with the final number driven by what is behind the stucco and under the slab.
Garage Conversion Fundamentals
On a 1950s stucco home near Del Rosa Avenue, our crew opened the detached garage for a JADU conversion and found cloth wiring, a cracked slab, and no waterproofing behind the original stucco. That is not an outlier in San Bernardino; it is the median outcome. We wrote a change order with photos and a fixed price for rewiring, a new slab section, and a fluid-applied membrane, and the homeowner approved it before we touched the walls. The final number matched the contract because the process made the hidden work visible and priced before it started.
Alley Access Advantage
Many older San Bernardino lots have alleys running behind the back fence, which means a detached ADU can be built at the rear of the property without the side-yard setback fights that kill attached additions. The unit can have its own address face, its own entrance, and enough separation from the main house to make it a true rental or a private multigenerational suite. We map the alley access, the utility connections, and the grading as part of every San Bernardino lot assessment.
Trusted Brands We Service in San Bernardino
Casita ADU Builders maintains builder relationships with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, and Plant Prefab, plus a Tuff Shed partnership for shed-conversion ADU projects. For San Bernardino customers we stock the local accessory and hardware lines these builds need, so a James Hardie fiber-cement exterior tie-in or a specific prefab connector does not stall a job for a week while parts ship from out of state. We recommend the right brand for the lot and the budget, never the only one on the shelf. If you have a specific prefab manufacturer in mind, we can price it specifically for your San Bernardino property.
Common ADU Builders Problems We See in San Bernardino Homes
- Garage conversions quoted without a test hole. A contractor quotes a conversion without opening the wall first, then “discovers” cloth wiring or dry-rotted framing after demo and adds thousands in change orders. We open a small inspection area before the quote, document what is there, and price the fix into the contract.
- Backyard structures that were never permitted. San Bernardino has a lot of casitas and add-ons that predate digital records and were never legally permitted. A simple remodel turns into a full legalization and code-upgrade scope. We check permit history on every San Bernardino project before writing the proposal.
- Plans that ignore the city’s two-ADU ordinance. Submitting plans for a second unit on a lot that cannot legally support both without a zoning variance wastes months and fees. We verify lot eligibility against San Bernardino’s current ordinance before design starts.
- Heat and cooling under-designed for the semi-arid climate. A poorly insulated ADU in San Bernardino becomes unusable from June through September. We specify insulation, glazing, and minisplit sizing for the actual summer loads this zip code sees.
Pricing for ADU Builders in San Bernardino, CA
Actual San Bernardino numbers, not national averages. A prefab ADU installation runs $150,000 to $250,000. A custom detached ADU runs $180,000 to $320,000. A garage conversion runs $110,000 to $210,000. A JADU (junior ADU) carved from an existing garage or attached space runs $80,000 to $140,000. What moves the number in San Bernardino specifically: the age and condition of the existing structure, whether the electrical panel needs replacement, whether the foundation is sound, and which prefab brand or custom design you choose. James Hardie exteriors add modest upfront cost but reduce long-term maintenance in a climate with intense sun exposure. Every estimate is free and written with line items. Call (877) 658-7475 for an exact quote on your San Bernardino lot.
We Also Serve Cities Near San Bernardino
Our crew regularly works across San Bernardino and the surrounding cities in the Inland Empire, including Muscoy, Highland, Loma Linda, and Rialto. Lot conditions and permit paths differ slightly from one jurisdiction to the next, and we price each city against its own code realities. If your property sits near the San Bernardino line in Highland or Loma Linda, call us and we will confirm coverage before you schedule a site visit.
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
It often does, because many 1950s San Bernardino garages still have cloth-insulated wiring that does not meet current code, and the city will require bringing the entire structure up to standard once it becomes a dwelling unit. A full garage rewire in San Bernardino typically runs $6,000 to $12,000 depending on size and panel condition. We inspect the wiring before quoting so that cost appears in the written estimate instead of arriving after demo. Call (877) 658-7475 to get your garage assessed.
Yes, in most cases a non-permitted structure can be legalized into an ADU, but it requires a full code-upgrade scope: foundation verification, electrical and plumbing replacement where needed, insulation, and Title 24 compliance. The cost typically runs $80,000 to $150,000 depending on the structure’s condition, which is still often less than demolishing and building new. San Bernardino has a lot of these older unpermitted casitas, and we have walked many through legalization successfully.
Yes, current San Bernardino rules allow one attached ADU and one detached ADU on a single-family lot, subject to lot size, setback, and other zoning constraints that we verify before design begins. Not every lot qualifies for both, and we will tell you plainly if yours does not. Call (877) 658-7475 and we can check your specific parcel against the city ordinance.
We write allowances into the original contract for the most common hidden upgrades older San Bernardino homes require, so the discovery is expected rather than shocking. If we find something outside the allowance, like a foundation crack or major termite damage, we document it with photos and give you a fixed-price written change order before any work continues. You approve the number before we touch the affected area, so the final contract still matches what you agreed to pay.
Yes, alley access is a significant advantage on older San Bernardino lots because it lets a detached ADU be placed at the rear of the property without fighting side-yard setbacks, and it can give the unit its own street-facing identity and separate entrance. We verify alley width, access clearances, and utility routing as part of the free site assessment. Call (877) 658-7475 to schedule yours.
If you are weighing an ADU on an older San Bernardino lot, start with a free inspection from a team that has opened enough of these walls to know what is behind them. Call (877) 658-7475 to schedule your free estimate with Casita ADU Builders.
Written by Nolan Treffert, Owner at Casita ADU Builders, serving San Bernardino and the surrounding Inland Empire.