Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across San Bernardino
A room addition or ADU in San Bernardino typically runs $45,000 to $130,000 for the addition itself, and $90,000 to $220,000 for a new detached ADU, depending on whether your lot triggers a fault-setback study, Wildland-Urban Interface framing rules, or hillside grading requirements. Those three variables show up more often here than almost anywhere else in the Inland Empire, and they change the number on your contract. We’re Barrett & Sons Construction, and we’ve been building in San Bernardino long enough to know which ZIP codes will ask for a geotechnical report before the foundation drawings get a single stamp.
If you’re thinking about opening up a 1940s tract home in 92405 or adding a second story near the Cajon Pass corridor, call Tom Barrett and his sons at (877) 610-1318. We’ll walk your lot, read the city’s checklist with you, and put every allowance in writing before a single wall comes down.
Why Barrett & Sons Construction Is San Bernardino’s Preferred Home Additions & ADU Company
We’re an owner-operated company founded in 1998. Tom Barrett’s name is on the truck, on the contract, and on the license, and his sons run the crews. When you call our office, a live person answers: not a voicemail box, not an out-of-state call center, not a franchise that routes you to whoever happens to be free. We serve San Bernardino from a scheduling office in the Inland Empire, and the crew that shows up at your door is the crew that stays on your job until the final inspection passes.
The 90-Day Done Right Promise is written on every contract we sign in San Bernardino. If something’s not done right, one call brings Tom back to make it right. No fine print, no argument. That promise matters more here than most places, because a bad foundation pour on expansive alluvial clay will show itself within two winters, and a rushed shear wall near the fault line will fail an inspection. We’d rather be the company that comes back than the company that dodges your call.
Every price change on a San Bernardino addition or ADU arrives as a written change order before work proceeds. The allowance that isn’t on paper is a surprise waiting for a date, and we don’t work that way. You’ll see the scope in writing, the allowances in writing, and every change order in writing. Ask anyone on your street, or look up the license number yourself.
Our Home Additions & ADU Services in San Bernardino
ADU Design & Permitting
The San Bernardino Development Services counter will not accept drawings for most lots north of Highland Avenue without a geotechnical report attached. Our pre-permit scope of work includes that report, because we know exactly what the reviewers ask for before they ask for it. We handle the full submittal package: fault-setback studies where the Alquist-Priolo maps apply, WUI checklists for the 92404 and 92407 foothills, and hillside grading rules where the lot slope demands them. You get one contractor responsible for the drawings, the permits, and the build.
New Detached ADU
A new detached ADU in San Bernardino runs $90,000 to $220,000. The spread is wide because a flat-lot build in 92410 looks nothing like a foothill ADU in 92407, where ember-resistant vents, non-combustible eave assemblies, and defensible-space grading can add five figures after the first submittal comes back redlined. We read the Wildland-Urban Interface checklist before we bid, so those costs appear in your first estimate instead of your fourth change order.
Second Story Additions
Adding a second story over a 1940s slab-on-grade ranch in central San Bernardino means confirming the existing foundation can take the new load path. That’s a soils report, a structural review of the stem wall, and often a corrected foundation detail. We’ve done enough of these in 92404 and 92405 to know what the shadows under the house will show us, and we write the allowance for it before we open the first wall. Near the Cajon Pass, the wind-load specification on a second-story addition gets stricter, and sheathing and fastening schedules change accordingly. We design to the San Bernardino wind zone, not the Riverside one.
Junior ADU & Interior Conversion
A junior ADU is the most affordable way to add a legal rental unit, usually built within the existing footprint of the home. In San Bernardino’s older tract neighborhoods, interior conversions often uncover deferred maintenance: outdated wiring, failed waterproofing, and undersized framing from decades of piecemeal repairs. We scope it, write the allowance, and show you the number before we swing a hammer. Then we pull the permit, pass the inspection, and hand you a signed final.
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 install materials you can look up, not mystery brands off a van. On San Bernardino hardscapes and outdoor spaces adjacent to ADUs, we routinely work with Techo-Bloc and Belgard: pavers and retaining wall systems that hold up to the valley’s 110-degree summers and the seasonal shifting of expansive soils. If the job calls for a structural retaining wall or paver driveway as part of the site prep, we’ll specify a Quikrete or Oldcastle product with the engineering data the city wants to see. We stock common parts locally for San Bernardino customers, which means less waiting when a foundation correction or a drainage detail changes the schedule.
Common Home Additions & ADU Problems We See in San Bernardino Homes
- Expansive soil movement under slab foundations. The flatlands of 92404 and 92405 sit on alluvial clay that swells in wet winters and shrinks through dry summers. A fresh stem wall on unengineered fill will crack within two winters. We take soil reports before we pour, not after the inspector flags the cracks.
- Fault-setback requirements north of Highland Avenue. San Bernardino sits closer to the San Andreas Fault than nearly any other major Southern California city. Lots in the Alquist-Priolo Earthquake Fault Zones often need a setback study and seismic engineering before the foundation design is approved. Contractors from Riverside or Fontana rarely bid it correctly on the first pass.
- Wildland-Urban Interface checklist in the northern foothills. ZIP codes 92404 and 92407 fall within California’s Very High Fire Hazard Severity Zone. That triggers ember-resistant vents, non-combustible eaves, and defensible-space grading on virtually every permit. If your first estimate didn’t mention those, the second one will.
- Unreinforced masonry adjacency near downtown 92401. A garage conversion in 92401 can trigger a mandatory seismic retrofit of the main house if the vehicle entry sits within a designated historic setback. Confirming that before you bid changes the entire contract.
Pricing for Home Additions & ADU in San Bernardino, CA
Our pricing reflects the actual conditions under your lot and inside your walls. Here’s what you can expect in the San Bernardino market:
| Project Type | Typical San Bernardino Range |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
What moves the number: whether you’re in a fault zone north of Highland, whether the foothill WUI checklist applies, whether the soils report finds expansive clay under the slab, and whether the existing structure needs a seismic retrofit before the addition ties in. Every one of those is a written allowance in our contract, not a surprise invoice at the end. The estimate is free, and it’s a real number based on your lot and your drawings. Call (877) 610-1318 to schedule yours.
We Also Serve Cities Near San Bernardino
Our crews live and work across the Inland Empire, including Muscoy, Highland, Loma Linda, and Rialto. If you’re just outside the San Bernardino city line, you’ll get the same local knowledge and the same written pricing from our Home Additions & ADU team. We don’t treat your permit like a stranger’s problem.
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 - Home Additions & ADU in San Bernardino
The permit doesn’t die, but the foundation design typically has to be revised and resubmitted with a soils report and a corrected stem wall or footing detail. We’ve handled this on 1940s tract homes across 92404 and 92405. The fix is a written change order with a price, a new drawing, and a re-inspection. Call (877) 610-1318 if your inspector just flagged movement and you want a second set of eyes on it.
Not every lot, but most lots north of Highland Avenue sit within or adjacent to an Alquist-Priolo Earthquake Fault Zone, and the city will reject drawings without a geotechnical report for those parcels. We include the study in our pre-permit scope of work so you’re not paying for a rejected submittal and a second round of engineering. The cost lands in your first estimate, not your third.
Often yes, if the existing electrical service can handle the new load and the garage has its own grounded circuit. But on 1960s slab-on-grade ranches in 92405, we’ve opened walls and found original knob-and-tube wiring still feeding ceiling outlets, which becomes a code violation as soon as the insulation is disturbed. In that case, the circuit gets rewired with a written change order. We stop work, show you the wire, get your signature, and complete the rough-in before any framing covers it.
Because they probably didn’t check whether the vehicle entry sits within a designated historic setback, and they almost certainly didn’t price the unreinforced masonry retrofit that the city can trigger on the main house before the ADU permit is issued. We’ve seen the redlined submittal come back. The lower quote becomes a second, much larger change order, or the contractor walks away. Our quote includes the retrofit allowance from the start. Call (877) 610-1318 for a straight number.
San Bernardino’s position at the mouth of the Cajon Pass means Santa Ana wind events here are measurably stronger than in neighboring valley cities. A second-story addition near the Pass corridor requires enhanced roof wind-load specifications, including specific sheathing and fastening schedules. We design to the San Bernardino wind zone from the first drawing, so the structural engineer’s sign-off doesn’t turn into a redesign. The free estimate includes the correct load path. Call (877) 610-1318 to get yours.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving San Bernardino and the Inland Empire since 1998.