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 West Hills
Home additions and ADU construction in West Hills typically run $45,000-$130,000 for a room addition, $90,000-$220,000 for a detached ADU, and $30,000-$80,000 for a garage conversion, with permits pulled and inspections signed on every eligible job. If you live in 91307 or 91308 and you’re weighing a second-story addition off Roscoe Boulevard or a detached ADU up a hillside lot near Bell Canyon, you need a contractor who already knows what LA County inspectors will flag before the first wall comes down. We’re Barrett & Sons Construction, owner-operated since 1998, and we’ve been through enough West Hills openings to know exactly what’s behind those 1960s ranch walls. Call (877) 610-1318 and Tom Barrett will walk you through what your specific street actually requires.
Why Barrett & Sons Construction Is West Hills’s Preferred Home Additions & ADU Company
Tom Barrett puts his name, address, and license number on every contract, and he’s been doing that for over 29 years. West Hills homeowners call us because when a surprise shows up inside a wall, the fix arrives as a written change order with a line-item allowance, not a new number at the final invoice. The last contractor a lot of our customers used told them permits were optional. We pull them on every eligible job, because the permit inspector works for you, not for me, and that inspection record is what protects your addition when you sell the house.
Our crews serving West Hills are background-checked and uniformed, and Tom’s sons are on-site most days. That means the person who shakes your hand at the estimate is the same family running the job. We answer our own phone 24/7, not a voicemail box and not an out-of-state call center. When a West Hills homeowner calls at 7 a.m. with a question about their ADU rough-in, a live person picks up. That matters when you’re waiting on an inspector who’s already scheduled.
Every completed job carries our written 90-Day Done Right Promise. If something isn’t right, one call brings Tom back. No fine print, no runaround. We live in the same county, not three states away.
Our Home Additions & ADU Services in West Hills
ADU Design & Permitting
Most West Hills ADUs start with a reality check on the lot. Hillside parcels near the Simi Hills interface add grading complexity, slope stability requirements, and retaining wall work that flatland Valley contractors rarely account for. We handle the full design and permitting path, including the Chapter 7A fire-safety review that LA County triggers when conditioned square footage increases. If your West Hills property sits inside the VHFHSZ boundary, your ADU plans will need Class A roofing, ember-resistant vents, and one-hour-rated assemblies. We plan for those from day one, so the permit doesn’t stall at plan check.
New Detached ADU
A new detached ADU on a West Hills lot is a different animal than one in Canoga Park. Santa Ana wind exposure through the mountain pass demands shear walls sized for 60 mph gusts, and ember-resistant soffit venting is not a suggestion in this zip code. We engineer the foundation and drainage together, because a hillside ADU that isn’t tied into proper retaining wall design will crack or shift within a few seasons. Expect $90,000-$220,000 for a complete detached ADU in West Hills, depending on site conditions and finishes.
Garage Conversion ADU
West Hills has thousands of attached garages sitting on post-WWII ranch homes built between the late 1950s and early 1980s. Many of them have slabs that were never engineered for living space, and some still carry 1994 Northridge earthquake damage that was never properly addressed. A garage conversion ADU in West Hills runs $30,000-$80,000, and the number moves based on what we find under the slab and behind the drywall. We inspect the existing footings before we quote, so the price reflects the actual condition of your garage, not a guess.
Junior ADU & Interior Conversion
If you have an underused family room or a large primary suite, a Junior ADU is often the fastest path to rentable square footage in West Hills. Interior conversions under 500 square feet avoid some of the site work that drives up detached ADU costs, but they still trigger the same Chapter 7A review if they add conditioned space. We handle the scope, the allowances, and the paperwork in writing, and we’ll tell you upfront if your interior conversion is going to require multi-pane windows or fire-rated assemblies before you commit to the project.
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 West Hills
We install windows and doors from Simonton, Ply Gem, and PGT on West Hills additions and ADUs, because those are brands with published performance ratings you can look up yourself. When a West Hills project needs impact-rated glazing to meet Chapter 7A requirements, PGT’s product line is already engineered for exactly that test. We don’t show up with mystery brands off the back of a van. We order what your permit requires, we verify the labels before installation, and we stand behind it with the same 90-Day Done Right Promise that applies to every Barrett & Sons job.
Common Home Additions & ADU Problems We See in West Hills Homes
- Chapter 7A surprise correction notices. A homeowner in West Hills plans a modest room addition, gets the permit rolling, and then LA County flags the project because the added square footage now requires fire-rated materials the original quote never included. That’s thousands in unplanned cost, and it happens constantly in 91307 and 91308 because the entire hillside edge sits inside the Very High Fire Hazard Severity Zone.
- Undersized shear walls from contractors who don’t know Santa Ana wind loads. West Hills funnels wind through the mountain pass where the Valley meets the Simi Hills. Shear walls spec’d for a flatland Valley project will fail inspection here. We’ve seen it happen to additions framed by contractors from Reseda who never accounted for 60 mph gusts.
- 1960s cloth-covered wiring and undersized rafters. On a Midwood Drive addition in West Hills, our crew opened the wall to find 1960s cloth-covered wiring and rafters that would not pass current shear codes. We wrote the electrical rough-in and structural reinforcement into the change order with a line-item allowance, got sign-off on the draw schedule, and had the inspector approve the new load-bearing beam and subfloor before drywall went up.
- Hillside additions that shift or crack. Sloped lots near Bell Canyon and along the Simi Hills edge put real stress on patio and sunroom additions. If the retaining wall and subfloor grading aren’t engineered together, the concrete cracks and the door frames bind within two wet seasons. We design them as one system, not two separate line items.
Pricing for Home Additions & ADU in West Hills, CA
West Hills pricing reflects what inspectors here actually require. A home addition runs $45,000-$130,000 depending on scope, site conditions, and finish level. A detached ADU runs $90,000-$220,000. A garage conversion runs $30,000-$80,000. Here are the line-item ranges we quote most often in West Hills:
| Project Type | West Hills Price Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
The single biggest variable in West Hills is whether your lot falls inside the VHFHSZ boundary. If it does, expect Class A roofing, ember-resistant vents, and one-hour-rated assemblies to add thousands in materials that the same project in Woodland Hills, just outside the boundary, would never require. We write every allowance into the contract up front, and any price change comes to you as a written change order before a single nail moves. Call (877) 610-1318 for a free estimate with real numbers for your street.
We Also Serve Cities Near West Hills
Our Home Additions & ADU team works throughout the western San Fernando Valley, including West Hills and the surrounding communities of Canoga Park, Woodland Hills, Calabasas, and Chatsworth. If you’re in one of those cities and weighing an addition or ADU, the same written change orders and 90-Day Done Right Promise apply. Call (877) 610-1318 and Tom Barrett will answer.
Serving West Hills, CA - Our Local Coverage Area
We’re based in the West 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 West Hills
Because West Hills sits inside LA County’s Very High Fire Hazard Severity Zone, any permitted addition that increases conditioned square footage triggers a Chapter 7A compliance review, which requires Class A roofing, ember-resistant vents, and one-hour-rated assemblies. The same project in neighboring Woodland Hills, just outside the VHFHSZ boundary, would never face that requirement. The November 2018 Woolsey Fire burned through the hillside edge of West Hills, and county inspectors have not relaxed those standards since. Call (877) 610-1318 if you want to know whether your specific parcel is inside the boundary before you start planning.
We inspect first, then we write it up. On a Midwood Drive addition, our crew found 1960s cloth-covered wiring and undersized rafters that would not pass current shear codes, so we wrote the electrical rough-in and structural reinforcement into the change order with a line-item allowance, got sign-off on the draw schedule, and had the inspector approve the new beam before drywall went up. An allowance that isn’t on paper is a surprise waiting for a date. Every Barrett & Sons contract separates allowances and change orders so you approve the actual number before we touch the work.
Yes, and it’s not optional if you want the permit signed. Many West Hills ranch homes built between the late 1950s and early 1980s sustained structural damage in the 1994 Northridge Earthquake, and some of that damage was never properly repaired. Current shear code is stricter than what those houses were built to, so an addition that ties into existing framing will likely need reinforcement to pass inspection. We plan for that in the quote, not after the walls are open. Call (877) 610-1318 for a free estimate that accounts for your home’s actual seismic history.
West Hills sits inside the Very High Fire Hazard Severity Zone along the Simi Hills-Santa Monica Mountains interface, while much of Woodland Hills sits outside that boundary. A permitted addition in West Hills that increases conditioned square footage triggers a Chapter 7A review requiring ignition-resistant cladding, ember-resistant vents, and one-hour-rated assemblies. The same square footage in Woodland Hills may never face those requirements. That’s a material difference in price, and if your contractor doesn’t know which side of the boundary line your street falls on, your quote is fiction. We know the boundary. That’s the whole job.
Because the allowance that isn’t on paper is a surprise waiting for a date, and West Hills ADUs have more legitimate surprises than almost any other project in the Valley. Chapter 7A material upgrades, hillside grading adjustments, and seismic reinforcement findings all move the number, and we want every one of those moves in writing before work proceeds. You approve the line item, you approve the draw schedule, and then we build it. No surprise invoices at the end, because the scope was never a secret. Call (877) 610-1318 and we’ll show you exactly what that looks like in a real West Hills contract.
Call Barrett & Sons Construction for Your West Hills Home Addition or ADU
If you’re planning a room addition, a detached ADU, or a garage conversion in West Hills, start with a contractor who already knows what LA County inspectors will require on your street. Tom Barrett founded this company in 1998, his sons run the crews, and every job comes with permits pulled, change orders in writing, and the 90-Day Done Right Promise on the contract. Call (877) 610-1318 today to schedule your free estimate. We’ll show you the real numbers for your parcel, including the Chapter 7A and hillside grading requirements that flatland Valley contractors miss.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving West Hills and the surrounding San Fernando Valley since 1998.