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 Chino Hills
If you’re weighing an ADU or a room addition in Chino Hills, the honest range is $45,000 to $130,000 for most attached additions, and $90,000 to $220,000 for a detached ADU built to California’s current WUI fire-resistive standards. What drives the spread isn’t the contractor’s mood, it’s your hillside pad, your retaining walls, and how much of the 1980s-era stucco framing has to come out before the new work goes in. We’ve been walking Chino Hills lots long enough to know the difference between a clean L.A. County-style build and what happens when you start grading behind a house in the VHFHSZ. Call (877) 610-1318 and Tom or one of his sons will tell you straight what your project actually involves.
Most of Chino Hills wasn’t built on flat ground. The home sites were graded into the hillsides, which means your addition has to satisfy both the city’s grading regulations and CAL FIRE’s wildland-urban interface requirements. A contractor who mostly works in Chino or Ontario will stare at those two sets of rules like they’re written in another language. They’re not written in another language. We read them every week.
Why Barrett & Sons Construction Is Chino Hills’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998 and he’s still the one who picks up the phone when you call the number on the truck. His sons run the crews that actually show up at your house in Chino Hills. That’s not a marketing line, it’s just how the business works, and it’s the reason homeowners in Los Serranos and the neighborhoods off Butterfield Ranch Road keep calling us back.
We publish our license number, our address, and our standing offers where anyone can check them. You won’t get a price on the phone from a call center in another state and then a different number when the crew arrives. Before a single nail moves, every scope change becomes a written change order. If it’s not on paper, it’s not real, and we’ll tell you that to your face.
We answer the phone 24 hours a day, every day. A live person, not a voicemail tree. For Chino Hills homeowners who’ve been burned by national outfits before, that alone is usually the difference between getting a straight answer and getting a runaround at ten o’clock at night.
Our Home Additions & ADU Services in Chino Hills
ADU Design & Permitting
Chino Hills sits almost entirely within a CAL FIRE-designated Very High Fire Hazard Severity Zone. That designation touches nearly every permit on an ADU, from the Class A roof assembly to the ember-resistant vents in the eaves. We handle the full design and permitting path through the City, including the WUI checklist, the hillside grading review, and the geotechnical report when your lot triggers one. You get a set of plans that will actually pass inspection the first time, not a set drawn by someone who’s never seen a Chino Hills hillside.
Garage Conversion ADU
A garage conversion in Chino Hills typically runs $30,000 to $80,000, depending on whether your garage sits on a post-tension slab or an older conventional slab with no vapor barrier. We see both across 91709. The 1985-to-2000 tract homes between Chino Hills Parkway and Grand Avenue usually have the post-tension slabs, which actually helps the conversion because the slab is thicker and less likely to heave under the expansive clay soils. That’s the kind of granular detail that changes your cost and your schedule, and it’s the kind of detail we put in writing.
New Detached ADU
A new detached ADU in Chino Hills is the most regulated build on this page: $90,000 to $220,000 is market-realistic once you account for fire-resistive wall assemblies, the electrical service upgrade, and the site utility trenching across graded terrain. You’ll also likely face a retaining wall review if your rear lot drops off toward the Chino Hills State Park side of the city. We’ve shepherded enough of these through the City’s Engineering Division to know exactly which reports they’ll ask for and which ones they won’t.
Junior ADU & Interior Conversion
If you have an oversized bedroom or a bonus room over the garage, a Junior ADU or interior conversion is often the fastest and least expensive path to a legal second unit in Chino Hills. We’ve done them for under $45,000 when the existing framing, plumbing stub-outs, and electrical panel were already in decent shape. The catch in this city is often the fire-rating: walls between a JADU and the main house have to meet a specific separation standard, and nobody discovers that by guessing. We check it before you spend a dollar.
And if you’re already planning an addition, talk to us about the kitchen or bath inside it. Our Kitchen Remodeling in Chino Hills work dovetails directly with most room additions, and Bathroom Remodeling in Chino Hills is often part of the same permit package when you’re adding square footage. You shouldn’t have to hire three companies for one addition.
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 Chino Hills
We carry premium materials you can look up before you sign: Simonton and Ply Gem windows are our go-to assemblies for Chino Hills additions because they hold their air-seal rating through the Santa Ana wind cycles that blow through the Chino Hills passes, and PGT impact-rated products get specified whenever the fire marshal’s review flags the glazing on a WUI-facing elevation. We stock and order parts for Chino Hills jobs specifically, so you aren’t waiting three weeks for a window sash that a national outfit forgot to order. When we install a brand, we install it correctly, and we stand behind it with the 90-Day Done Right Promise.
Common Home Additions & ADU Problems We See in Chino Hills Homes
- Hillside retaining wall failures. The 1980s-era concrete and CMU retaining walls that terrace hundreds of Chino Hills lots are failing under hydrostatic pressure and swelling clay. When your addition sits behind one of those walls, the city will require a geotechnical soils report and a full grading permit before you can touch anything. We’ve seen homeowners spend thousands on plans that died at the Engineering Division because nobody flagged the wall.
- Inconsistent pre-1991 permit records. Chino Hills incorporated in 1991, and many homes built before that have permit and inspection records that are incomplete or missing altogether. That complicates the scope for any addition, because the city may require a verification inspection of the existing structure before it approves new work. You want a contractor who knows how that conversation goes.
- Ember intrusion and ignition-resistant cladding. The wind-driven embers that roll through the Chino Hills passes in October don’t care how nice your addition looks. If a wall assembly, vent, or roof edge doesn’t meet the WUI standard, the permit dies and your money is gone. We treat the fire-resistive details as load-bearing parts of the plan, not afterthoughts.
- Expansive clay and foundation movement. The hillside soils across 91709 swell and contract seasonally, which puts chronic stress on post-tension slabs and stem walls. An addition that isn’t designed for that movement can shear away from the existing structure within a few years. We evaluate the soil conditions and the existing foundation before we draw anything, because the alternative is a cracked wall and a regret that costs more than the report.
Pricing for Home Additions & ADU in Chino Hills, CA
Here’s the straight math. An attached room addition in Chino Hills typically lands between $45,000 and $130,000 depending on the size, the foundation conditions, and whether the elevation faces the fire severity zone. A detached ADU runs $90,000 to $220,000. A garage conversion spans $30,000 to $80,000, and a Junior ADU or interior conversion can come in under $45,000 when the existing bones are good.
What moves the number: retaining wall engineering, geotechnical soils reports, WUI-compliant wall and roof assemblies, electrical service upgrades, and the occasional pre-1991 record verification inspection. None of that should be a mystery. We give you a written, line-item price before work starts, and every change after that arrives as a written change order. Call (877) 610-1318 for a free estimate. If you have a written estimate from someone else, ask about our Free Second Opinion offer.
We Also Serve Cities Near Chino Hills
Our crews work Chino Hills neighborhoods from Los Serranos to the streets off Carbon Canyon, and we also serve Chino, Diamond Bar, and Yorba Linda. If you’re just over the city line and you want a contractor who actually understands the Home Additions & ADU in Chino Hills terrain, we’re the same crew either way. For more on how we handle additions, see our Home Additions & ADU team page.
Serving Chino Hills, CA - Our Local Coverage Area
We’re based in the Chino Hills 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 Chino Hills
An attached home addition in Chino Hills typically costs $45,000 to $130,000. A detached ADU runs $90,000 to $220,000, a garage conversion $30,000 to $80,000, and a Junior ADU often falls under $45,000. The numbers shift based on your hillside lot, retaining wall condition, and WUI fire-resistive requirements. Call (877) 610-1318 for an exact written quote, free of charge.
Yes. Every eligible job includes permits pulled and inspections signed. In Chino Hills that often means a grading permit, a geotechnical soils report, and a WUI fire-resistive review through the City’s Engineering Division and the fire authority. The permit inspector works for you, not for us, which is exactly why we want them on the job.
A garage conversion typically runs 12 to 16 weeks from permit approval to final inspection. A detached ADU usually takes 6 to 9 months, and an attached addition 3 to 6 months, depending on the hillside conditions and how fast the City processes the WUI and grading reviews. We’ll give you a written schedule with the written price, and every schedule change follows the same rule: it comes to you on paper before it happens.
Because Chino Hills is almost entirely a Very High Fire Hazard Severity Zone built on graded hillside pads. The flat cities next door don’t carry the same CAL FIRE WUI requirements, the same expansive clay soils, or the same aging retaining wall inventory. When a Chino Hills addition requires a geotechnical report, a retaining wall review, and ember-resistant venting all at once, the cost stacks up. It’s not a markup, it’s the actual work the city requires.
Yes. Every Barrett & Sons Construction job, including additions and ADUs in Chino Hills, is backed by our written 90-Day Done Right Promise. If it’s not done right, Tom comes back and makes it right, one call. You’ll also get our published offers: $40 off any repair over $200, a Free Second Opinion on any written estimate, and no trip charge inside the county. Call (877) 610-1318 and ask for Tom.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Chino Hills since 1998.