Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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Before
AfterFast, Reliable Home Additions & ADU Across Westchester
A home addition in Westchester typically runs $45,000-$130,000, while a full ADU build ranges from $90,000-$220,000. Most projects take 4-8 months from permit to final inspection, though Westchester’s unique position under LAX flight paths can add a federal review step that inland LA contractors never handle. Call (213) 221-0788 to schedule your free estimate.
We’ve worked the coastal mesa neighborhoods of Westchester since Rowan Construction Group was founded in 2007, and we know the difference between building here and building inland. The marine layer that rolls in from the Pacific three to four miles away keeps humidity elevated year-round, accelerates wood rot at sill plates, and corrodes standard fasteners faster than anywhere in the LA basin. Our crews dispatch from the Los Angeles office and carry stainless hardware and the current LAWA approved-product schedule as standard equipment for Westchester jobs.
Why Rowan Construction Group Sherman Oaks Is Westchester’s Preferred Home Additions & ADU Company
Westchester homeowners research contractors the way they research appliances, and we built our process for exactly that customer. Across 4,000-plus projects since 2007, every one started with a written price before any work began. Our 365-Day Done Right Promise is printed on every page, backed by a terms page, not an asterisk.
We answer calls with a live person 24/7, and every visit produces a documented photo record included as standard. Our crews are background-checked and uniformed, and we pull permits and pass inspections as a matter of course. Under Clause 1 of The Haven Standard, the price is written before anyone starts; under Clause 3, no change proceeds without a signed change order. That discipline is why our projects finish within a few percent of the agreed number.
Our Home Additions & ADU team serves Westchester specifically because the neighborhood’s conditions, codes, and federal requirements demand local experience. We keep the current FAA Form 7460-1 filing requirements and LAWA soundproofing product lists on file, not in a filing cabinet at headquarters.
Our Home Additions & ADU Services in Westchester
Second Story Additions
Second story additions in Westchester face a constraint almost no other LA neighborhood shares: LAX’s FAA Part 77 airspace influence zone. Any new construction pushing above modest height thresholds may require filing FAA Form 7460-1, a federal Notice of Proposed Construction or Alteration. Inland contractors who’ve never filed one can lose months discovering this requirement mid-permit. We file it as routine.
On a second-story addition off La Tijera near the Westchester bluffs, our crew pulled fascia with hot-dip galvanized fasteners that had rotted and corroded within eight years in the marine-layer damp - the same detail that looked fine a mile inland. We stripped to the sheathing, rebuilt with stainless structural screws and a sealed 316-grade flashing detail, and passed inspection sign-off on the first walk. The coastal-spec hardware costs more upfront. It costs far less than rebuilding fascia twice.
New Detached ADU
A new detached ADU in Westchester runs $90,000-$220,000, with site prep and utility tie-ins often driving the variance. The neighborhood’s 1940s-1950s tract housing sits on lots with aging galvanized supply lines and original sewer laterals that may need replacement before the ADU can tie in. We test and document existing conditions before quoting, so the price you sign reflects what we found, not what we guessed.
Roofing and window specs for a Westchester ADU must account for both salt-laden air and the LAWA soundproofing program. The program’s approved-product schedule for windows and HVAC penetrations is not optional here, and showing up with a non-listed unit, even a high-quality one, can stall permits indefinitely. We source from the current LAWA list and specify marine-grade finishes on exposed metal.
Garage Conversion ADU
Garage conversion ADUs in Westchester typically fall between $30,000-$80,000, making them the most accessible entry point for homeowners adding rental income or family space. The catch: many Westchester garages share slab and roof conditions with the main house, and the same asbestos-containing materials found in 1950s ranch interiors often hide in garage floor tiles, pipe insulation, and textured ceilings.
We test for asbestos before demolition, not after. Finding it mid-project forces a licensed-abatement change order, a permit hold, and a schedule hit that can add weeks. Our quotes include contingency language for abatement when testing indicates likelihood, so the number we write is the number you plan for.
Junior ADU & Interior Conversion
Junior ADUs, carved from existing interior space with a separate entrance, suit Westchester’s smaller ranch footprints where lot coverage limits rule out detached structures. These conversions run toward the lower end of the addition range but still require full permitting, utility separation, and compliance with LA’s fire and egress codes. We handle the JADU designation paperwork and coordinate with LA Building & Safety on the owner-occupancy verification that the city requires.
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.
Before
AfterTrusted Brands We Service in Westchester
Our sourcing depth runs across fifty-plus vetted brands, and we specify them by name in every written quote. For Westchester’s coastal conditions, we regularly source Dvele and Plant Prefab for ADU panelized builds that ship with marine-grade exterior finishes pre-applied. Mighty Buildings’ 3D-printed units offer non-corroding composite wall assemblies that perform well in persistent humidity. Boxabl’s fold-out modules can work for detached ADUs on tight Westchester lots where crane access is limited by overhead power lines or narrow driveways. We stock and source locally for Westchester, not from a central warehouse three counties away, which means replacement materials arrive in days, not weeks, when a field condition demands a change.
Common Home Additions & ADU Problems We See in Westchester Homes
- Corroded fasteners and bleeding rust stains. Electroplated or standard galvanized hardware spec’d for inland LA corrodes within a few years in Westchester’s marine-layer damp. We see it on railings, flashing, and fascia fasteners. We specify stainless or hot-dip galvanized with a marine-grade topcoat, and we document the fastener grade in the written scope so there’s no substitution at the supply house.
- Asbestos discovery mid-demolition. Westchester’s pre-1950s ranch homes contain asbestos floor tile, pipe insulation, and popcorn ceilings at rates that surprise homeowners who assumed their 1955 build was clean. We test before permit application, not after the sledgehammers swing, and we hold a licensed abatement contractor relationship for when results come back positive.
- LAWA non-compliance killing permits mid-stream. Contractors unfamiliar with Westchester show up with excellent windows that aren’t on the current LAWA soundproofing program approved-product schedule. The permit gets held. The job stops. We check the current schedule before bidding any sound-attenuation scope and write the approved product numbers into the quote.
- Wood rot at sill plates and fascia. The coastal mesa’s elevated humidity softens sill plates and rafter tails on aging ranch homes, often hidden by intact siding. Our pre-construction inspection includes moisture-meter readings at critical junctions, and we rebuild with pressure-treated or composite lumber where the existing stock is compromised.
Pricing for Home Additions & ADU in Westchester, CA
We put the number in writing before anyone picks up a tool. Below are the ranges we see for Westchester’s market, calibrated for coastal-spec materials and the federal and local compliance steps this neighborhood requires.
| Service | Westchester Price Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
| Window Replacement | $4,500-$15,000 |
| Impact Window Installation | $8,000-$25,000 |
| Roof Replacement | $8,000-$20,000 |
The gap between a coastal-spec quote and an inland-spec quote for the same square footage in Westchester typically runs 8-15%. That premium buys stainless or 316-grade hardware, marine-grade finishes on exposed metal, LAWA-compliant window assemblies, and fasteners that won’t rot your fascia from the inside out within a decade. The cheap spec always costs more. It just costs later, and usually on someone else’s watch.
Every quote is flat-priced with a written scope and written warranty. Bring a competitor’s written estimate and we’ll review it line by line at no charge. Call (213) 221-0788 for your free estimate.
We Also Serve Cities Near Westchester
Our crews work across the West LA corridor and the San Fernando Valley. We also serve Home Additions & ADU in Westchester neighboring communities including Sherman Oaks, Van Nuys, Encino, and Studio City. Each city’s conditions differ, and we adjust specs accordingly, but the same written-price-first discipline applies everywhere we work.
Serving Westchester, CA - Our Local Coverage Area
We’re based in the Westchester 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 Westchester
Yes, if your project exceeds height thresholds within LAX’s FAA Part 77 airspace influence zone, you must file FAA Form 7460-1 for federal review. Most Westchester second-story additions and some taller detached ADUs trigger this requirement, while inland LA projects rarely do. We file this form as standard practice for qualifying Westchester projects and build the 30-60 day federal review timeline into our schedule. Call (213) 221-0788 and we’ll check your specific lot and proposed height against current FAA criteria during the free estimate.
The coastal-spec quote runs 8-15% higher because it specifies stainless or 316-grade fasteners, marine-grade metal finishes, LAWA-compliant window assemblies, and pressure-treated or composite lumber at critical rot points. An inland-spec build with standard galvanized hardware and generic windows will corrode, leak, and require premature replacement in Westchester’s marine-layer damp. We quote the spec that lasts. Call (213) 221-0788 for a line-item written quote that names every material grade.
It may. Westchester’s 1940s-1950s tract housing contains asbestos floor tile, pipe insulation, and popcorn ceilings at high rates, and LA Building & Safety requires licensed abatement before demolition or structural modification if testing confirms it. We test during pre-construction, not after permits are pulled, and we include abatement contingency language in our written quotes when likelihood is elevated. Call (213) 221-0788 and we’ll review your home’s build year and visible materials during the free estimate.
Yes, but only with products on the current LAWA Airport Soundproofing Program approved-product schedule, which specifies dual-pane laminated assemblies that also carry marine-grade frame finishes. Standard coastal windows without LAWA approval won’t pass permit; standard LAWA windows without coastal-grade hardware will corrode. We cross-reference both requirements before specifying and write the approved product numbers into your quote. Call (213) 221-0788 to see the current schedule and applicable models.
We write the full price before work starts, test for asbestos and structural conditions before quoting, and require signed change orders for any deviation. No work proceeds on a change until the change order is signed, Clause 3 of The Haven Standard. This administrative discipline, which Haven acquired Rowan for in 2007, has kept our projects within a few percent of the agreed price across 4,000-plus jobs. Call (213) 221-0788 for a written estimate with no obligation.
Written by Grant Rowan, Owner at Rowan Construction Group, serving Westchester since 2007.