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 Los Serranos
Most Los Serranos homeowners call us with the same question: can I add space to this house without it turning into a six-month headache? The honest answer is yes, if the contractor understands what Los Serranos permits actually require. We’re Barrett & Sons Construction, and we’ve been building Home Additions & ADU projects in the 91709 ZIP long enough to know that the Chino Hills fire zone rules, the clay soil, and the age of the homes near the Los Serranos Country Club all change how a job gets priced and permitted. A typical room addition here runs $45,000 to $130,000, an ADU $90,000 to $220,000, and a garage conversion $30,000 to $80,000. Call (877) 610-1318 for a free estimate, and we’ll walk the property with you before you sign anything.
Why Barrett & Sons Construction Is Los Serranos’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998, and his sons run the crews today. That matters in Los Serranos because the permit inspector here will check attic vents for 1/16-inch mesh screens, look at your shear wall nailing pattern, and ask about your foundation design. We know the answers before the inspector shows up. Out-of-area crews do not, and homeowners pay for that gap in failed inspections and change orders written after the fact.
We answer our own phone. Not a call center. When a Los Serranos homeowner calls at 6 a.m. worried about a foundation crack that appeared overnight, Tom or one of his sons picks up. Every job gets a written scope, written allowances, and written change orders before any new work begins. The 90-Day Done Right Promise is printed on every contract: if something is not done right, one call brings Tom back.
Local homeowners around the Country Club and the hillside tracts off Butterfield Ranch Road have seen our crews on their streets for years. Ask anyone. Or look up the license number yourself. We publish Tom’s name, address, and license number on every estimate.
Our Home Additions & ADU Services in Los Serranos
ADU Design & Permitting
Every ADU permit in Los Serranos gets reviewed under California’s Wildland-Urban Interface fire zone rules. That means our plans specify Class A roofing assemblies, ignition-resistant exterior cladding, and 1/16-inch corrosion-resistant mesh over every attic and sub-floor vent before the city will even schedule a foundation inspection. We handle the full design, structural engineering, and permit submittal, and Tom walks the plans with you line by line before anything is filed.
Garage Conversion ADU
Converting an attached or detached garage in Los Serranos runs $30,000 to $80,000 depending on whether the existing slab has a capillary break, whether the walls meet current shear standards, and whether the electrical panel has capacity. Homes built before the 1980s near the Country Club often need panel upgrades and subfloor corrections. We write those into the allowance schedule up front so the price does not surprise you mid-job.
New Detached ADU
A new detached ADU in the 91709 ZIP runs $90,000 to $220,000. The range is wide because expansive clay soils in the Chino Hills often require engineered foundations rather than standard slabs. We bring in a soils report, design the footing and stem wall for the actual ground movement your lot sees, and coordinate the WUI-compliant exterior package from day one. You get a fixed price with change orders only if you change the scope.
Junior ADU & Interior Conversion
A Junior ADU inside an existing Los Serranos home is often the fastest path to rental income or space for an aging parent. These conversions run from roughly $45,000 to $130,000 depending on whether we are opening walls, adding a kitchenette, or upgrading wiring and plumbing to current code. Interior conversions still trigger fire-zone requirements if any exterior wall is touched. We plan for that from the first walkthrough.
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 Los Serranos
We do not install mystery materials off a van. When we waterproof a shower or a foundation wall in Los Serranos, we use Schluter systems because they hold up to the wet-dry cycles our clay soil creates. Roof assemblies on additions and ADUs get GAF materials, which meet the Class A fire rating the WUI code requires. Sterling and Grohe fixtures go into bathrooms where water pressure and hard water are real concerns. We stock common parts locally so a warranty call does not wait on a shipment from three states away.
Common Home Additions & ADU Problems We See in Los Serranos Homes
- Out-of-area crews fail the WUI vent inspection. A contractor from flat Chino or Ontario frames the addition with standard builder-grade attic vents, then the Chino Hills inspector flags the missing 1/16-inch corrosion-resistant mesh. The fix means tearing out finished soffit work.
- Second-story additions crack existing slabs. Many 1980s hillside tract homes were built on slabs never designed for an added floor. Without a foundation analysis and engineered retrofit, the new load cracks the original concrete.
- Garage conversions stall on subfloor corrections. Old garages near the Country Club often have slabs poured directly over expansive clay without a capillary break. Inspectors catch it, and the floor has to come out and get re-poured with proper drainage before rough-in can continue.
- Opening a wall reveals outdated wiring. Mid-century Los Serranos homes frequently have original knob-and-tube or undersized aluminum branch circuits. Once the inspector sees an open wall, current code applies. We budget an electrical allowance on every older-home addition.
Pricing for Home Additions & ADU in Los Serranos, CA
Here is what we see in the Los Serranos market right now. These are not teaser prices meant to get a signature; they are the ranges our written estimates fall into based on the homes we have measured in this ZIP.
| Project Type | Typical Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
| Kitchen Remodel | $14,000-$45,000 |
| Bathroom Remodel | $9,000-$28,000 |
What moves the number in Los Serranos specifically: WUI-compliant exterior materials, engineered foundations for expansive clay, and the condition of the framing and wiring inside older homes near the Country Club. We write every allowance into the contract. If we open a wall and find something the original scope did not cover, you get a written change order with a price before we touch it. Call (877) 610-1318 to schedule a free estimate, and Tom will walk the property with you.
We Also Serve Cities Near Los Serranos
Our crews work throughout the Chino Hills area, including Home Additions & ADU in Los Serranos, Chino Hills, Chino, Diamond Bar, and Yorba Linda. If you are a few minutes west in Chino or up the hill in Diamond Bar, the same Tom Barrett who answers the phone in Los Serranos will be the one walking your job.
Serving Los Serranos, CA - Our Local Coverage Area
We’re based in the Los Serranos 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 Los Serranos
Los Serranos sits inside California’s Wildland-Urban Interface fire zone, which flat Chino is not. Every new ADU and addition in the 91709 ZIP must use 1/16-inch corrosion-resistant mesh over attic and sub-floor vents to stop embers from entering during Santa Ana wind events. The Chino Hills inspector specifically checks this detail. Call (877) 610-1318 and we will pull the WUI checklist for your address before you file anything.
Once the inspector sees inside the wall, current electrical code applies to everything visible. If your home has original knob-and-tube or undersized aluminum branch circuits, you will need a panel and wiring upgrade on that circuit at minimum. We build an electrical allowance into every Los Serranos addition estimate for exactly this reason, so the cost is approved on paper before the wall comes down. Call (877) 610-1318 for an exact allowance based on your home’s age.
We order a soils report and a foundation analysis before we design anything structural. The clay in the Chino Hills swells and shrinks with seasonal wet-dry cycles, and a second story adds load the original slab was never designed to carry. In most cases we specify an engineered retrofit, piering, or a new foundation system for the addition. That cost is written into your allowance schedule up front, not discovered after framing starts.
No. If any exterior wall, vent, or roof assembly is touched, the WUI requirements apply to the entire project. An existing attached garage in the 91709 ZIP still needs the 1/16-inch mesh vents and ignition-resistant cladding where walls are opened or replaced. We plan for that from day one so the permit does not stall. Call (877) 610-1318 and we will tell you exactly what applies to your garage.
We schedule exterior concrete pours for early morning, use cold-water mixing and evaporation retarders, and adjust the mix design for high-heat conditions. The Chino Hills summer heat can flash-set concrete and ruin a slab if the crew is not careful. We also sequence roofing work during cooler parts of the day when Santa Ana winds allow. Schedule your free estimate at (877) 610-1318 and we will build the weather into your timeline.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Los Serranos and the surrounding Chino Hills area since 1998.