Fast, Reliable New Detached ADU Across Westchester
A new detached ADU in Westchester typically costs $220,000-$380,000 all-in, including design, permitting, and construction, with most projects moving from signed contract to certificate of occupancy in 8-14 months. We’re Ellery ADU Studio, a design-build practice led by Nadia Ellery, and we’ve been navigating Westchester’s unique permitting landscape since 2015 - the year California’s ADU laws first shifted. Our New Detached ADU team coordinates dispatch from our Los Angeles office, with crews serving Westchester locally. Call (424) 551-7706 to schedule your free estimate - every project receives a written price before any work starts, per Haven Standard Clause 1.
Why Ellery ADU Studio Los Angeles Is Westchester’s Preferred New Detached ADU Company
We’ve designed, permitted, and built over 900 ADUs since 2015, and a significant share of those have been in Westchester’s 90045 zip and the surrounding postwar ranch tracts. Our clients here tend to be homeowners who bought between 2015 and 2022, paid a premium for the neighborhood’s proximity to LAX and the coast, and now want to convert their 6,000-7,500 sq ft lot into rental income or family housing without selling into a high-interest market.
What Westchester homeowners tell us they value most: we name the dollar range on the first call, we document every site visit with a photo record they receive by email, and we handle the FAA Part 77 airspace study and LAX noise-contour attenuation as scoped line items - not surprises that appear after design is complete. Our 365-Day Done Right Promise is backed in writing before the project starts. A live person answers our phones 24/7, and we offer a Free Second Opinion on any written estimate already in hand.
Our New Detached ADU Services in Westchester
Custom Built ADU
A custom built ADU in Westchester runs $260,000-$380,000 all-in, drawings through final inspection. This is the right path when your lot has constraints that prefab can’t accommodate - a tight setback near the Kentwood bluffs, an FAA Part 77 height restriction that demands a low-profile roof, or the need to match the horizontal board siding on your 1952 ranch. We design the permit set in-house, build from that same set, and hold one contract at one written price. No designer-builder blame gap.
Prefab ADU Installation
Prefab ADU installation in Westchester typically ranges $220,000-$320,000, including site prep, foundation, utility tie-in, and all local permitting. We specify and coordinate systems from Abodu, Cover, and Dvele - brands whose modules we know down to the crane-access requirements and the LA Department of Building and Safety approval status. On a standard 6,500 sq ft lot near Westchester Parkway, a prefab unit can often be set and weathered-in within 48 hours of delivery, but the real timeline driver is still the site: grading, the 200-amp utility upgrade, and any FAA or noise-contour layer.
Modular ADU
Modular ADU construction in Westchester falls in the $240,000-$350,000 range. Unlike site-built framing, modular units arrive with interior finishes largely complete, which compresses the construction phase but demands precise foundation prep. In Westchester’s open-graded soils - common from the Kentwood area west toward the bluffs - we often need to re-grade and install a drywell drainage system before the slab is poured. We scope this during the first site visit and write it into the contract price. Under Haven Standard Clause 5, that scope is locked at signing.
Studio ADU & 1-Bed & 2-Bed ADU
Studio ADUs in Westchester start around $220,000; 1-bed units typically run $240,000-$300,000; 2-bed configurations range $280,000-$380,000 depending on square footage and utility complexity. The 1-bed and 2-bed options are particularly popular with Westchester homeowners whose adult children work at LAX or in the Playa Vista tech corridor and need independent housing without leaving the neighborhood. Every configuration we quote includes the full permit set, the documented photo record, and the written 365-Day Done Right Promise.
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 Westchester
We specify and coordinate prefab and modular systems from Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie - all within the same single contract that covers design, permitting, and construction. For Westchester clients, this means we maintain current LA Department of Building and Safety approval documentation on Abodu and Cover units, and we know which James Hardie siding profiles best match the postwar ranch aesthetic common from West 80th Street to the Kentwood bluffs. No chasing between a designer, a prefab dealer, and a separate contractor.
Common New Detached ADU Problems We See in Westchester Homes
- FAA Part 77 height studies derailing two-story designs. Because Westchester sits directly under LAX’s primary approach corridors, much of the neighborhood falls within FAA Part 77 airspace surfaces that impose hard roof-height ceilings. A detached ADU near the runway side of the lot can be capped at a lower elevation than the identical building a few blocks east toward Inglewood. We flag this on the first site visit and commission the height study before design proceeds.
- Electrical panels and galvanized supply lines that can’t carry the load. The original 60-100 amp panels and aging galvanized water supply in these 1949-1962 tract homes almost never support a detached ADU. We scope the 200-amp underground feed and copper or PEX replacement as line items in the initial quote, not as change orders after framing starts.
- LAX 65 dB CNEL noise-contour attenuation rules. Portions of Westchester fall within this contour, which triggers mandatory sound-attenuation construction standards: STC-rated windows, extra wall insulation, and mechanical ventilation in lieu of operable windows. This adds $8,000-$15,000 to a typical build and is a code layer most LA neighborhoods never encounter. We identify contour status from the address and build it into the permit set from day one.
- Grading and drainage surprises on open-graded soils. Westchester’s marine-layer humidity plus the neighborhood’s sandy, open-graded soils mean re-grading and drywell installation are common prerequisites to slab work. On a recent 600 sq ft detached ADU off West 80th Street near the Kentwood bluffs, we had to re-grade the pad and tie new drainage to a drywell before the slab went in. The original 100-amp panel and galvanized service had to be replaced with a 200-amp underground feed, and because the lot backed onto the LAX 65 dB CNEL contour we built the walls with STC-rated glazing and mechanical ventilation in lieu of operable windows. Total added scope over a stock detached build ran well past the garage-conversion allowances, mostly in sitework and utilities.
Pricing for New Detached ADU in Westchester, CA
| ADU Type | Typical All-In Range | Key Cost Drivers in Westchester |
|---|---|---|
| Studio ADU (prefab) | $220,000-$280,000 | Foundation, utility upgrade, FAA height study if applicable |
| 1-Bed ADU (prefab or modular) | $240,000-$320,000 | Module size, crane access, noise-contour attenuation |
| 2-Bed ADU (custom or modular) | $280,000-$380,000 | Square footage, full kitchen, multiple HVAC zones |
| Site prep & utilities (add-on) | $25,000-$55,000 | Panel upgrade, re-grading, drywell, underground feed |
| LAX noise-contour attenuation | $8,000-$15,000 | STC glazing, extra insulation, mechanical ventilation |
These ranges reflect what we’ve actually contracted in Westchester over the past three years. Every project is quoted with a written price before any work begins - Haven Standard Clause 1 - and the scope is locked at signing under Clause 5. No door-side upsells. No scope creep. Call (424) 551-7706 for your free estimate.
We Also Serve Cities Near Westchester
Our crews work throughout the west side and beyond Westchester itself, including Los Angeles, Culver City, West Los Angeles, and Santa Monica. Each city carries its own permitting nuances - Culver City runs its own planning department independent of LA, while Santa Monica has additional design-review layers - and we scope those differences into every quote.
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 - New Detached ADU in Westchester
Only if the lot falls within FAA Part 77 airspace surfaces, which covers much of Westchester under LAX’s primary approach corridors. A two-story or raised ADU design will need the study before the City of LA accepts the permit application; single-story builds at standard height often clear without it. We verify airspace status from your address during the first site visit and commission the study if needed - it’s a scoped line item, not a surprise. Call (424) 551-7706 and we’ll check it for free.
Any lot inside the contour triggers the rules; the boundary runs roughly parallel to the airport side of Westchester, affecting areas near Westchester Parkway and the Kentwood bluffs most directly. We pull the CNEL map from the LAX Airport Land Use Compatibility Plan and confirm your lot’s status before design starts. If you’re inside, the attenuation package - STC-rated windows, extra wall insulation, mechanical ventilation - adds $8,000-$15,000 and is non-negotiable for permit approval. Call (424) 551-7706 and we’ll verify your status.
Almost never. The 60-100 amp panels and galvanized supply lines original to Westchester’s 1949-1962 tract housing were sized for a 1,100-1,600 sq ft home with minimal electric load. A detached ADU with kitchen, laundry, and HVAC requires a 200-amp service and underground feed to the new structure. We scope this upgrade in every Westchester quote where the existing panel hasn’t already been replaced. The $8,000-$18,000 utility line item is written into your contract price before signing. Call (424) 551-7706 for a written quote.
A garage conversion starts on an existing slab; a detached ADU starts on open ground, and Westchester’s open-graded soils - sandy, fast-draining, common from Kentwood west - often need re-grading and a drywell drainage system before the foundation can be poured. The marine-layer humidity compounds this: poor drainage accelerates wood rot and mold in the crawl space or slab edge. On that 1949 ranch off West 80th Street, we re-graded the entire rear third of the lot and tied drainage to a drywell before the slab went in. We photograph the soil conditions on the first visit and write the grading scope into your price. Call (424) 551-7706 to schedule a site evaluation.
No. Abodu and Cover units still require full City of LA permits, including the FAA Part 77 height study and LAX noise-contour attenuation if your lot triggers those layers. What prefab does compress is the construction phase: the module arrives 80-90% complete, so weathering-in happens in days rather than weeks. But the permitting timeline - design review, plan check, corrections, inspection scheduling - remains governed by local code, not the manufacturer. We handle all of it under one contract, including the manufacturer’s coordination. Call (424) 551-7706 for a written price that includes every local layer.
Ready to price a new detached ADU on your Westchester lot? Call (424) 551-7706 to schedule your free estimate. You’ll receive a written price before any work starts, a documented photo record on every visit, and the 365-Day Done Right Promise backed in writing - the Haven Standard we’ve operated under since 2015.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Westchester and the greater Los Angeles area since 2015.