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 Calabasas
Adding square footage or building an ADU in Calabasas typically runs $45,000-$130,000 for a room addition and $90,000-$220,000 for a detached ADU, and the permit path here is genuinely different than what your brother-in-law dealt with in Woodland Hills. Calabasas sits almost entirely inside a Very High Fire Hazard Severity Zone, which means every structural project clears two desks: city building and fire marshal review under Chapter 7A. We have worked the gated communities off Parkway Calabasas, the hillside lots above Mulholland Highway, and the older pocket neighborhoods near Old Town. Call (877) 610-1318 and we will walk the property with you before you spend a dime on drawings.
Why Barrett & Sons Construction Is Calabasas’s Preferred Home Additions & ADU Company
Tom Barrett started this company in 1998 and his sons run the crews. That matters in Calabasas because the approval gauntlet here is not something a national outfit’s rotating project manager is equipped to navigate. The architectural control committee at The Oaks of Calabasas can send an ADU design back three times. The fire marshal will flag ember-resistant vent details that a flatland contractor never priced. Our Home Additions & ADU team has been through enough Calabasas permits to know which submittal gets kicked back and why.
We are not the cheapest bid you will get. We are the bid that already has the geotechnical report, the Chapter 7A siding upgrade, and the AFCI panel swap written into it before you sign. Reviews from Calabasas customers repeatedly mention the same thing: the price on the contract was the price on the final invoice. That happens because every allowance is written down and every change order is priced and approved in writing before the next nail moves. If it is not done right within 90 days, Tom comes back. One call. That is the 90-Day Done Right Promise, printed on every contract.
We answer the phone 24/7 with a live person, and our scheduling for Calabasas is coordinated from our Los Angeles office with local crews running the jobs. Calls are not routed to an out-of-state center.
Our Home Additions & ADU Services in Calabasas
Here are the four services Calabasas homeowners call us about most, and what each one actually involves in this city.
ADU Design & Permitting
The Calabasas ADU permit process layers city building review on top of fire marshal review and, for most residents, a gated-community architectural committee. That sequence routinely adds 6-8 weeks compared to neighboring cities. We handle drawings, structural calcs, Title 24 energy compliance, and the Chapter 7A materials list as one package, and we file everything in the order the city actually wants to see it. That sequencing is the difference between a permit in eight weeks and a permit in eight months.
New Detached ADU
A new detached ADU in Calabasas runs $90,000-$220,000, and the range swings mostly on slope and soil. On hillside lots above Las Virgenes Road, the city routinely requires a geotechnical report and then rejects standard slab designs in favor of deepened caissons or continuous grade beams. That is a five-figure line item a flatland contractor’s quote simply will not contain, and it is why our quotes do. We also spec ember-resistant vents and Class A roofing from the first draft, because the fire marshal will not sign final inspection without them.
Garage Conversion ADU
Garage conversions in Calabasas typically fall between $30,000-$80,000. The older homes here, many built in the mid-80s through the 2000s, often have garage slabs poured thinner than current ADU code requires, which means saw-cutting, compacting, and repouring sections. We also see a lot of pre-2018 structures where the fire marshal uses the permit as a trigger to require ignition-resistant upgrades on the adjacent elevation. That is not scope creep. That is the city protecting your home, and it belongs in the quote from day one.
Junior ADU & Interior Conversion
A junior ADU built inside the existing footprint of a Calabasas home is the fastest path to a rentable unit, and often the least disruptive. We convert bonus rooms, oversized laundry rooms, and underused dens into code-compliant JADUs with a kitchenette, separate entrance, and its own smoke and CO detection tied to the main panel. These conversions frequently expose outdated wiring once walls come open, which is exactly the scenario we have planned for with written allowances instead of verbal promises.
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 Calabasas
We install materials you can look up by name. For Calabasas ADUs and additions we regularly use Schluter waterproofing systems in wet areas, Sterling plumbing fixtures, and Grohe faucets and shower valves. These are not mystery brands off the back of a van. If a sub-trade has a supply-house relationship in the valley, we can pull parts same-week, which keeps Calabasas jobs moving when a national crew would be waiting on a truck from out of state.
Common Home Additions & ADU Problems We See in Calabasas Homes
Opening up walls in Calabasas turns up the same handful of problems often enough that we plan for them before demolition starts.
- Undersized electrical panels: Homes built in the 1990s around Calabasas Park commonly have 100-amp panels that are already at capacity. Adding a bedroom, bath, or ADU triggers a panel swap and AFCI protection requirements, which is a written line item in our allowances.
- Chapter 7A ignition-resistant assemblies: Any addition touching an exterior wall on a pre-2018 home can trigger a fire marshal requirement to re-side the affected elevation with ignition-resistant materials. Flatland contractors miss this, and it shows up as a nasty surprise at final inspection.
- Expansive clay soils on graded hillsides: Lots cut into the slopes above Mulholland Highway and Las Virgenes Road frequently need geotechnical reports and deepened foundations. Standard slab designs get rejected. The fix is caissons or grade beams, and the cost arrives before we pour, not after.
- Gated community architectural review: The Oaks of Calabasas and similar HOAs often have design review boards with their own submittal calendars. An ADU design that the city would approve in a week can sit in committee for three rounds and add two months to the timeline.
Pricing for Home Additions & ADU in Calabasas, CA
Here is what we currently see in the Calabasas market, based on jobs we have quoted and built in 91302 and 91372.
| Project Type | Typical Range in Calabasas |
|---|---|
| Home Addition / Room Addition | $45,000-$130,000 |
| Second Story Addition | $45,000-$130,000 |
| ADU Construction (Detached) | $90,000-$220,000 |
| Garage Conversion ADU | $30,000-$80,000 |
What moves the number most in Calabasas is slope and code status. A flat-lot garage conversion on a post-Woolsey rebuild lands at the low end. A detached ADU on a hillside cut into expansive clay with a pre-2018 primary home adjacent to it lands at the high end, because the geotech, the caissons, the Chapter 7A siding, and the panel upgrade are all in scope. We give free estimates and every number is written down. Call (877) 610-1318 to schedule yours.
We Also Serve Cities Near Calabasas
While this page is specifically for Calabasas homeowners, our crews regularly work in Home Additions & ADU in Calabasas and nearby communities including Woodland Hills, West Hills, Topanga, and Canoga Park. If you live just over the city line, the same owner-operated crew and written-change-order policy applies.
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
Mostly no. Flat lots in Calabasas neighborhoods like Calabasas Hills or the areas around El Camino Real typically do not trigger a geotechnical report for a single-story addition on an existing foundation line. But lots with any meaningful cut or fill, particularly above Mulholland Highway or along the northern slopes toward the Santa Monica Mountains, routinely do. If you are unsure whether your lot counts as flat, call (877) 610-1318 and we will look at the parcel before you pay an engineer.
It can, and the trigger is usually any work that touches an exterior wall or roof assembly. The fire marshal in Calabasas applies Chapter 7A requirements to the portions of the building you are altering, which often means upgrading the affected elevation to ignition-resistant siding, adding ember-resistant vents, or bringing the roof edge into compliance. This is not optional once the permit is pulled. We price it into the estimate so it does not ambush you at final inspection.
Plan on roughly four to six months for a detached ADU permit in Calabasas, assuming no architectural committee is involved. With a gated community review board like the one at The Oaks of Calabasas, add six to eight weeks. Agoura Hills, which does not sit in the same fire hazard severity zone in all areas and has fewer HOA-controlled communities, often processes the same permit in half the time. The difference is the dual-review structure, not the quality of the city staff.
Expect an electrical change order. A 1990s Calabasas home almost always has a 100-amp panel that is already at capacity, and adding a second story triggers AFCI requirements and often a panel replacement. On a recent hillside job above Las Virgenes Road, our crew found exactly that, plus a fire marshal flag on Type V siding that required re-siding the affected elevation. Because the contract had a written allowance for electrical and a defined change order process, the homeowner saw the additional cost in writing and approved it before rough-in stopped. We never spring a number on you after the fact.
Usually yes, with some planning. Most Calabasas communities restrict construction to weekday daytime hours, which actually makes phased room additions more practical than elsewhere, because the work happens while you are out and quiets down by evening. The bigger question is dust and access. For addition projects that tie into the main living area, we build a temporary weather-tight divider wall and run a zip-wall containment so you can keep using the kitchen and bedrooms. We can tell you on the first visit whether staying in the home during your specific project is realistic.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Calabasas since 1998.