Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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After
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AfterFast, Reliable Home Additions & ADU Across Calabasas
Home additions and ADU construction in Calabasas typically runs $45,000-$130,000 for a room addition and $90,000-$220,000 for a detached ADU, with garage conversions falling between $30,000-$80,000. The process here moves through more layers than most of Los Angeles County: city building permits, fire marshal review, and often the architectural control committee of your gated community. We’ve been walking Calabasas homeowners through that process since 1998, and every job comes with permits pulled, inspections signed, and every price change in writing before work starts. Call (877) 610-1318 to schedule your free estimate.
Why Barrett & Sons Construction Is Calabasas’s Preferred Home Additions & ADU Company
Tom Barrett put his name on the truck in 1998, and his sons run the crews today. When you call, a live person answers, 24/7. Not a voicemail box, not an out-of-state call center. When we give you a price, it’s the price you’ll see on the final invoice, because every scope change, every allowance adjustment, every single variation arrives as a written change order before a nail moves.
We know what Calabasas throws at a construction project. The hillside lots above Las Virgenes Road cut into expansive clay that shifts with the seasons. The Santa Ana wind events that funnel through the Santa Monica Mountain passes from October through December change how we schedule and fire-harden a site. And the gated communities like The Oaks of Calabasas have architectural control committees with their own standards for roof lines, window styles, and exterior materials. If you’ve been burned by a contractor who quoted one price on the phone and handed you another at the door, you’ll notice the difference. Tom publishes his name, his address, and his license number. Look it up before you sign anything.
Every completed job carries the written 90-Day Done Right Promise. If something isn’t done right, one call brings Tom back. That’s not a slogan; it’s on the contract.
Our Home Additions & ADU Services in Calabasas
ADU Design & Permitting
An ADU in Calabasas is not a simple plan-and-permit process. The city’s Very High Fire Hazard Severity Zone designation layers fire marshal review on top of building permits, and many Calabasas neighborhoods inside gated communities add a third layer: architectural control committee approval. We handle the full design, the geotechnical report when the hillside soils require it, the permit package, and the inspections. The permit inspector works for you, not for us. That’s why we like him. We want the inspection signed off as much as you do.
Garage Conversion ADU
Converting an attached or detached garage is usually the fastest path to a rental unit or in-law suite in Calabasas, and it typically runs $30,000-$80,000 depending on whether you’re doing a straight interior conversion or opening walls to add plumbing and a full kitchen. Homes built from the mid-1980s through the 2000s often have generous garage footprints in the Spanish Colonial and Mediterranean styles that dominate Calabasas, but older pre-2018 structures may need ember-resistant vents and ignition-resistant exterior upgrades as part of the conversion. We quote those in writing before work begins, not as a surprise at the end.
New Detached ADU
A ground-up detached ADU in Calabasas runs $90,000-$220,000. On hillside lots above Mulholland Highway, the city routinely requires a geotechnical report before it issues grading or foundation permits, and inspectors commonly reject standard slab designs in favor of deepened caissons or continuous grade beams. That’s a cost and timeline surprise for contractors whose experience is limited to flatland San Fernando Valley work. It’s a standard Tuesday for us. We design the foundation for the soil from day one, so the permit doesn’t stall.
Junior ADU & Interior Conversion
A junior ADU built within the existing footprint of your Calabasas home is the most economical path to a legal rental unit, typically ranging $45,000-$90,000 depending on whether you’re carving out space from an existing bedroom and bath or building a small addition. Calabasas zoning allows JADUs in most single-family zones, and the permitting path is lighter than a detached ADU because there’s no separate structure. That said, the fire-safety review still applies, and we pull every permit and sign every inspection on these just as we would on a full addition.
We also handle full Home Additions & ADU projects beyond these four: room additions, second story additions, sunrooms, and enclosed patios. And if you’re already rethinking the inside of the house, our Kitchen Remodeling in Calabasas and Bathroom Remodeling in Calabasas teams work side by side with our addition crews, so you can phase the project or do it all at once.
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 Calabasas
We install materials you can look up. On ADU and addition projects in Calabasas, that means GAF roofing systems built for Class A fire ratings, Schluter waterproofing membranes in any wet areas, and Grohe or Sterling fixtures in kitchens and baths. We don’t load mystery brands off the back of a van. Every brand we carry is a name you can research, and we stock the Calabasas-appropriate options: ember-resistant venting, Class A-rated roof assemblies, and ignition-resistant exterior details that meet Chapter 7A Wildland-Urban Interface code. When you need a material warranty honored three years from now, you’ll be glad the name on the box is real.
Common Home Additions & ADU Problems We See in Calabasas Homes
- Post-Woolsey retrofit gaps. Homes rebuilt after 2018 meet current WUI standards, but many pre-2018 structures in the 91302 and 91372 ZIP codes still have older vents, siding, and roof assemblies that the fire marshal flags during ADU review. We bring those up to code as part of the addition, not as a separate surprise invoice.
- Expansive clay soil on hillside lots. The clay soils above Las Virgenes Road and Mulholland Highway swell and shrink with moisture, which cracks standard slabs. The city often requires a geotechnical report and deepened caissons or grade beams, and we price that into the initial scope, not a change order later.
- Gated community approval delays. In communities like The Oaks of Calabasas, the architectural control committee has its own review process on top of the city’s. Their turnarounds vary by community, and if your previous contractor didn’t know that, your timeline went sideways. We map the approval path before we submit drawings.
- Santa Ana wind season conflicts. October through December brings the wind events that drove the Woolsey Fire, and the site fire-safety plans required during that window affect everything from welding to adhesive curing. We schedule around the wind calendar where possible, and plan for it where we can’t.
Pricing for Home Additions & ADU in Calabasas, CA
Here are the honest numbers for Calabasas. A room addition runs $45,000-$130,000. A detached ADU runs $90,000-$220,000. A garage conversion runs $30,000-$80,000. A junior ADU or interior conversion runs $45,000-$90,000. What moves the number within those ranges: hillside soil conditions and the foundation system they require, the fire-hardening upgrades your existing structure needs, the finish level, and the approval timelines of your specific HOA or architectural committee.
Every estimate is line-item and written. Every allowance is written. Every change order is written. The allowance that isn’t on paper is a surprise waiting for a date, and we don’t do that to Calabasas homeowners. Call (877) 610-1318 for a free estimate on your specific project. We also offer a permanent 10% Senior & Veteran discount and a Free Second Opinion on any written estimate you’ve already received from another contractor.
We Also Serve Cities Near Calabasas
If you’re in Woodland Hills, West Hills, Topanga, or Canoga Park, this same crew covers your Calabasas area project from the same dispatch line. We schedule across the west San Fernando Valley and the canyon communities every week, and the estimates are free everywhere we work. Call (877) 610-1318 and we’ll get you on the calendar.
Serving Calabasas, CA - Our Local Coverage Area
We’re based in the Calabasas 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 Calabasas
A home addition in Calabasas runs $45,000-$130,000, and a detached ADU runs $90,000-$220,000. Garage conversions fall between $30,000-$80,000. Your specific number depends on soil conditions, fire-safety retrofit requirements, and the finish level you choose. Call (877) 610-1318 for a line-item quote, and bring any other written estimate you’ve received; we offer a Free Second Opinion on it.
Yes. Every eligible job includes permits pulled and inspections signed, including fire marshal review and any HOA or architectural control committee approvals required in communities like The Oaks of Calabasas. The permit inspector works for you, not for us. We want that inspection signed off just as much as you do. Call (877) 610-1318 to talk through your project’s specific approval path.
A typical detached ADU in Calabasas takes six to twelve months from design to final inspection. A garage conversion usually runs three to seven months. The approval layers here, city building permits, fire marshal review, and HOA architectural committees, add weeks that flatland cities don’t have. We map the full timeline before we start so you’re not surprised. Call (877) 610-1318 for a realistic schedule on your specific project.
Yes. Calabasas hillside lots above Las Virgenes Road and Mulholland Highway sit on expansive clay that the city typically requires a geotechnical report before it issues grading or foundation permits. We design for deepened caissons or continuous grade beams from the first drawing, so your permit doesn’t stall and your price doesn’t move later. Call (877) 610-1318 and we’ll look at your lot.
Not unless you change the scope, and even then, every price change arrives as a written change order before work happens. No surprise invoices at the end. No unilateral changes. We’ve operated that way since 1998, and the 90-Day Done Right Promise means one call brings Tom back if anything isn’t right. Call (877) 610-1318 for a free estimate.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Calabasas and the surrounding communities since 1998.