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 Highland
A home addition in Highland typically runs $45,000 to $130,000, while a new detached ADU lands between $90,000 and $220,000. The spread is wider here than in flatland Inland Empire cities, and it has everything to do with geology: alluvial fan soils, the San Andreas Fault through the foothills, and CAL FIRE’s Very High Hazard zone north of Baseline. We know those conditions because we work them every month. Call (877) 610-1318 and Tom Barrett or one of his sons will walk your lot before you spend a dime.
Highland isn’t a simple build site. It’s a mountain-valley transition zone where a five-figure difference in final cost can hinge on whether your lot sits north or south of Baseline Street. That’s why we start every addition and ADU estimate the same way: we look at your parcel’s geology, fire zone, and existing foundation before we put a single number in writing. If you want a contractor who already knows what the San Bernardino County plan checker will flag on a 1972 ranch slab, you’re in the right place.
Why Barrett & Sons Construction Is Highland’s Preferred Home Additions & ADU Company
We’re not a franchise dispatching strangers from three counties away. Tom Barrett founded this company in 1998, and his sons run the crews. When we quote an ADU off Baseline or a second-story addition near Highland Avenue, the person who shook your hand is the same person who signs the permit and shows up at rough-in. Calls get answered by a live person, day or night, and the license number, address, and names are published for anyone to look up before signing anything.
Highland homeowners have told us the same story more times than we can count: another contractor said a geotech report was “optional,” or quoted one price and arrived with another. We don’t work that way. Every scope, every allowance, every price change arrives as a written change order before work happens. The permit inspector works for you, not for me; that’s why I like him. Our Home Additions & ADU team has pulled and passed inspections on dozens of Highland jobs, including hillside lots that got flagged for WUIMP fire-hardening mid-plan. We know how to prepare you for that before it becomes a surprise.
Our Home Additions & ADU Services in Highland
ADU Design & Permitting
In Highland, ADU permitting is where projects live or die. A lot north of Baseline triggers Wildland-Urban Interface fire-hardening reviews that most cities don’t touch, and a lot on alluvial fan deposits usually needs a soils report before the city will even look at your plans. We handle that full sequence: design, geotech coordination, fire-hardening submittals, and the Alquist-Priolo fault-zone checks that apply to the northern edge of the 92346 zip code.
New Detached ADU
A detached ADU in Highland runs $90,000 to $220,000 depending on fire-zone requirements, foundation engineering, and site access. On hillside lots, expect ember-resistant vents, non-combustible roofing, and ignition-resistant siding as baseline costs, not upgrades. We frame with stainless steel connectors at every load-bearing point and spec hot-dip galvanized fasteners because salt air from the valley’s old agricultural runoff patterns and Santa Ana grit eat standard zinc hardware in under a decade here.
Garage Conversion ADU
Garage conversions in Highland’s pre-1987 tracts almost always hit a foundation question: the original slab was never designed for occupancy, and current code requires seismic anchorage before change-of-use sign-off. We’ve seen final inspections stall over exactly this. $30,000 to $80,000 is the real range for a Highland garage conversion, and a chunk of that goes to the engineering and anchorage work that a flatland quote skips.
Junior ADU & Interior Conversion
Attached JADUs and interior conversions are the smart play for Highland homeowners who want rental income or multi-generational space without triggering a full geotech circus. But even an interior conversion in a 1960s or 1970s tract needs a structural check: expansive clay under an unreinforced slab can crack partition walls within three years. We design for that from day one.
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 Highland
We install materials you can look up. For hardscape tie-ins around a new ADU or room addition, we use Techo-Bloc and Cambridge Pavers. For concrete work tied to foundations and flatwork, Quikrete and Oldcastle products show up on our Highland jobs because they hold up to the drainage and thermal swings we get at the mountain-valley line. We stock common repair parts for our Highland service runs so you’re not waiting three weeks on a back-ordered fastener while your unpermitted room sits open to the wind.
Common Home Additions & ADU Problems We See in Highland Homes
- Slab cracks on alluvial soils. A sunroom or room addition poured on an unmodified slab without a geotech report cracks and sinks within three years as expansive clay swells with foothill drainage. We see it on 1960s and 1970s ranches all over the 92346.
- Ember intrusion north of Baseline. An ADU with standard zinc-coated hardware and a basic asphalt shingle roof will fail ember intrusion during the first strong Santa Ana event. It passes the original permit because the fire-zone review wasn’t applied, and then the embers find the ridge vent.
- Garage conversion foundation stalls. A pre-1987 garage gets rough-in approval, then the final inspection freezes because the original slab lacks seismic anchorage now required for occupancy. The homeowner is left with open walls and a red tag.
- Second-story racking on 1980s frames. A second-story addition on a ranch frame shows racking at the original top plate because the load path was never upgraded to current Alquist-Priolo standards. We fix the load path before we frame, not after the drywall cracks.
Pricing for Home Additions & ADU in Highland, CA
Here’s what we quote in Highland right now, based on the soil, fire zone, and foundation conditions we actually find on your street:
| Project Type | Highland Price Range |
|---|---|
| Garage Conversion ADU | $30,000 - $80,000 |
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| New Detached ADU | $90,000 - $220,000 |
The gap between a $45,000 room addition and a $130,000 one in Highland isn’t about markup. It’s about geotech piers versus a standard slab, fire-hardened roof and siding versus basic spec, and hot-dip galvanized fasteners versus the zinc-coated hardware that rusts through on a salt-air-and-Santa-Ana lot. Cheap spec costs more within a decade. We price the coastal-spec version up front so you’re not paying for it twice. Call (877) 610-1318 for a free estimate with every allowance in writing.
We Also Serve Cities Near Highland
Our crews cover Highland and the surrounding foothill communities. We work regularly in San Bernardino, Muscoy, Redlands, and Loma Linda, but this page is written for Home Additions & ADU in Highland because the soil, fault-zone, and fire-zone rules here aren’t the same as anywhere else in the Inland Empire.
Serving Highland, CA - Our Local Coverage Area
We’re based in the Highland 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 Highland
Because Highland sits directly on alluvial fans draining the San Bernardino Mountains, and the city’s plan checkers know that expansive clay and liquefaction-prone soils are present across the 92346. A geotech report is the only way to prove your slab won’t crack and sink when seasonal drainage from the foothills hits your lot. We coordinate the geotech submittal as part of every Highland addition or ADU permit package. Call (877) 610-1318 for an estimate that includes the engineering you actually need.
North of Baseline Street, expect $15,000 to $40,000 in additional WUIMP fire-hardening costs: non-combustible roofing, ember-resistant vents, and ignition-resistant siding. Your neighbor a mile south in the valley floor may not face any of those requirements. We identify your fire zone during the first site visit so that number is in the written estimate, not a change order after framing starts.
Usually not, and this is the most common stall we fix. Pre-1987 garage slabs in Highland were poured for vehicles, not occupancy, and current code requires seismic anchorage and a geotech-supported foundation before final sign-off. Some slabs can be reinforced and anchored; many need a new engineered slab. The $30,000 to $80,000 range we quote includes the foundation work. Call (877) 610-1318 and we’ll inspect your slab for free inside the county.
Santa Ana gusts regularly exceed 60 mph near the mountain-valley interface, and they carry grit that strips standard zinc-coated fasteners and drives embers into any gap. That’s why we spec marine-grade rated panels, hot-dip galvanized hardware, and ember-resistant vents on every Highland addition and ADU we build. The cheap inland spec fails within a decade; we don’t install it.
Because Loma Linda sits on stable valley alluvium away from the mountain front, while Highland’s north side is in the Alquist-Priolo Earthquake Fault Zone and the city requires a soils report, seismic anchorage, and a load-path upgrade to the original frame. That engineering, plus the heavier hardware and fire-hardened envelope, adds thousands to the same floor plan. It’s not markup; it’s code, and we put every dollar of it in the written estimate.
Call Barrett & Sons for Your Highland Home Addition or ADU
We’ll walk your lot, check your fire zone, and give you a written estimate with every allowance, scope, and change order down to the fastener spec. Tom Barrett publishes his name, address, and license number, and his sons will be the ones framing your ADU. Call (877) 610-1318 to schedule your free estimate.
Written by Tom Barrett, Owner at Barrett & Sons Construction.