Fast, Reliable New Detached ADU Across Westchester
A new detached ADU in Westchester typically runs $285,000-$485,000 all-in, from permit set through final inspection, depending on whether you choose custom stick-built, prefab, or modular construction. We’re Nadia Ellery’s team at Ellery ADU Studio, and we coordinate design, permitting, and build from our Los Angeles office with crews serving Westchester directly. If you’re on a 5,000-7,500 sq ft lot with a 1950s Ranch-style home - the standard Westchester footprint - your project faces specific conditions most contractors miss: LAX noise-contour sound-attenuation requirements, potential FAA Part 77 airspace review for two-story units, and existing cloth-wrapped wiring or unsealed slabs that trigger code upgrades once walls open. Call (213) 329-7167 to schedule your free estimate. We’ll bring a written price, not a callback promise.
Why Ellery ADU Studio West Hollywood Is Westchester’s Preferred New Detached ADU Company
We’ve designed, permitted, and built over 900 ADUs since 2015, the year California’s ADU laws shifted. Westchester projects make up a significant share of our Los Angeles portfolio because the neighborhood’s post-WWII housing stock and by-right lot sizes create near-perfect conditions for detached units - but only if the permit set accounts for the local noise contour and existing conditions from the start.
Our Westchester clients receive the same documentation we provide everywhere: a written price before any work starts (Haven Standard, Clause 1), a documented photo record on every site visit, and the 365-Day Done Right Promise backed in writing. No designer-versus-builder blame gap. One contract, one price, one accountable studio.
Dispatch and scheduling are coordinated from our Los Angeles office, and our crews serve Westchester locally. Response time to Westchester inquiries is same-day during business hours, and a live person answers calls 24/7 - no voicemail queue, no callback that doesn’t materialize.
We also offer a Free Second Opinion on any written estimate already in hand. Bring us another contractor’s scope and we’ll flag what’s missing, what’s overstated, and what Westchester-specific conditions they’ve overlooked.
Our New Detached ADU Services in Westchester
Custom Built ADU
Custom stick-built construction gives you full control over layout, materials, and finish level. In Westchester, this means we engineer for the 65-70 dB CNEL noise contour from the first sketch - specifying STC-rated wall assemblies, dual-pane windows that match or exceed any existing LAX Residential Sound Insulation Program upgrades on your main house, and continuous insulation details that a City of LA plan checker can verify against the OITC documentation. A typical custom detached ADU in Westchester runs $320,000-$485,000 all-in, drawings through final inspection. We don’t pour footings until the permit set is approved and the written price is locked.
Prefab ADU Installation
We specify and coordinate prefab systems from Abodu, Cover, and other manufacturers within our single-contract model. Prefab ADU installation in Westchester typically costs $285,000-$380,000, including foundation, utility tie-ins, and the sound-attenuation package required for the LAX corridor. The factory build shortens on-site time, which matters on Westchester’s narrow side-yard lots where staging space is tight. We handle the FAA Part 77 screening if your design exceeds one story, and we verify that the manufacturer’s STC ratings integrate with your existing home’s insulation envelope.
Modular ADU
Modular construction - built to IRC standards in a factory, then craned onto your foundation - suits Westchester lots with alley access or wide enough driveways off streets like Manchester Avenue or Sepulveda Boulevard. Modular ADU projects in Westchester generally range $295,000-$410,000. We coordinate Dvele, Mighty Buildings, or Plant Prefab modules with the same permit-set rigor as stick-built: noise-contour compliance, utility load calculations for your existing panel, and vapor-management details for the marine-layer humidity that sits on this neighborhood most mornings.
Studio ADU
A studio ADU - single open room, kitchenette, full bath - is the most common detached unit we permit in Westchester. The compact footprint fits standard 5,000 sq ft lots while preserving rear yard space. Studio ADUs in Westchester typically run $285,000-$355,000. Even at this scale, the LAX noise contour applies: we specify acoustic-rated doors, sealed wall cavities, and mechanical ventilation that meets both energy code and the higher STC threshold. One-story studios under 16 feet generally avoid FAA Part 77 review, which speeds plan check.
1-Bed & 2-Bed ADU
One-bedroom and two-bedroom detached ADUs add rental income potential or multigenerational flexibility. In Westchester, these range $325,000-$485,000 depending on square footage and finish level. Two-story designs trigger the FAA airspace determination we mentioned - we submit this concurrently with the City of LA permit set so it doesn’t delay your timeline. Bedroom count drives ventilation requirements, and with Westchester’s persistent marine layer, we specify continuous exhaust and supply ventilation in every unit, not just code-minimum bath fans.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Before
AfterTrusted Brands We Service in Westchester
We specify and coordinate prefab and modular systems from Abodu, Cover, Tuff Shed, and James Hardie within our single-contract model. For Westchester’s noise-contour requirements, we favor James Hardie fiber-cement cladding for its mass and durability in salt-air conditions, and we pair Abodu or Cover units with upgraded window packages that hit the STC ratings City of LA expects. Our crew stocks common connection hardware and flashing details locally, so when a Westchester project needs a field modification to match existing LAX Sound Insulation Program upgrades, we don’t wait on factory lead times. Every brand we specify is documented in the permit set before construction starts, not substituted later without written approval.
Common New Detached ADU Problems We See in Westchester Homes
- Cloth-wrapped wiring and undersized panels. Westchester’s 1940s-60s housing stock often contains cloth-insulated branch circuits and 100-amp services that can’t carry a new detached ADU load. The permit triggers a full service upgrade, including trenching to the new panel location. We inspect the existing panel and main feed during our first site visit, photograph everything, and write the upgrade into the contract as a line-item allowance so you’re not surprised when the walls open.
- Unsealed slabs and missing vapor barriers. Original garage slabs and patio pours in Westchester were never designed for conditioned habitable space. Without a continuous vapor-management detail beneath the new detached unit, moisture wicks through the slab, fails air-quality testing, and breeds mold in wall cavities. We core-test existing concrete and specify polyethylene barriers or vapor-retarder admixtures before any framing begins.
- STC and OITC documentation mismatches with LAX Sound Insulation Program upgrades. Many Westchester homes received dual-pane windows and attic insulation through the LAX Residential Sound Insulation Program. If your new detached ADU’s noise-attenuation package doesn’t match or exceed those existing upgrades, the City of LA plan checker flags the inconsistency and stops the permit. We verify your Program participation status during design and engineer the new unit’s envelope accordingly.
- FAA Part 77 airspace delays on two-story designs. Any detached ADU in Westchester that exceeds 16 feet in height may require FAA notification and airspace determination before City of LA will issue a building permit. We submit the FAA screen concurrently with our permit package, not as an afterthought, and we design with height limits that avoid the review when possible.
Pricing for New Detached ADU in Westchester, CA
Here’s what new detached ADU construction costs in Westchester’s current market:
| Project Type | Typical All-In Range |
|---|---|
| Studio ADU (custom stick-built) | $285,000 - $355,000 |
| Studio ADU (prefab/modular) | $285,000 - $340,000 |
| 1-Bedroom ADU | $325,000 - $410,000 |
| 2-Bedroom ADU | $380,000 - $485,000 |
| Two-story ADU (with FAA determination) | $395,000 - $485,000 |
These ranges include design, permit set, all City of LA fees, construction, and final inspection. What moves the number: foundation type (slab-on-grade vs. raised), utility trenching distance, existing panel upgrade requirements, and the sound-attentration package level required for your specific lot’s position in the CNEL contour. Under Haven Standard, Clause 1, every project is quoted with a written price before any work begins. No “call for a quote” - the quote comes to you, itemized, before you sign. Call (213) 329-7167 for your free estimate.
We Also Serve Cities Near Westchester
Our New Detached ADU team works throughout the metro area. We also design, permit, and build in Westchester‘s neighboring communities: West Hollywood, Studio City, Los Angeles, and North Hollywood. Each city has its own ADU ordinance nuances, noise contours, and existing-housing conditions, and our permit sets are tailored accordingly - never copy-pasted.
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 design exceeds one story or 16 feet in height, which places it within FAA Part 77 notification zones for LAX approach corridors. Most single-story studio and one-bedroom ADUs avoid this requirement entirely. For two-story designs, we submit the FAA airspace determination concurrently with the City of LA permit set so it doesn’t add timeline. Call (213) 329-7167 and we’ll verify your lot’s specific requirements during the free estimate.
Yes. If your home received dual-pane windows, attic insulation, or other upgrades through the LAX Residential Sound Insulation Program, your new detached ADU must match or exceed that noise-attenuation envelope in its STC and OITC documentation. A mismatch gets flagged at plan check. We verify your Program participation status during design and engineer the new unit’s wall assemblies, windows, and ventilation accordingly. Call (213) 329-7167 for an exact quote - estimates are free.
Cloth-wrapped wiring, 100-amp panels that won’t carry the new load, unsealed concrete slabs with no vapor barrier, and original framing that doesn’t meet current energy code. On a 1952 Ranch near 88th Street and Anza Avenue, our crew found exactly this combination. We stopped, documented with photos, and issued a written change order for full rewire and continuous vapor management before pouring footings. The homeowner approved same-day, and final inspection passed with the plan checker noting our STC documentation matched the existing LAX Sound Insulation Program envelope. We build allowances for these conditions into every Westchester contract. Call (213) 329-7167 to schedule your site evaluation.
Yes. Westchester’s persistent coastal marine layer, which often doesn’t burn off fully in winter months, creates vapor-drive conditions that standard construction details don’t address. We specify continuous mechanical ventilation, vapor-retarder underslab protection, and moisture-resistant sheathings as standard on every Westchester detached ADU - not upgrades, not options. The permit set includes these details so the inspector can verify them in the field. Call (213) 329-7167 for a written quote that includes the full specification.
Yes, if your lot meets City of LA height and setback requirements, but the second story triggers FAA Part 77 airspace review and requires more intensive sound-attenuation engineering for the LAX 65-70 dB CNEL contour. We design two-story detached ADUs in Westchester regularly and handle both the FAA submission and the enhanced STC documentation as part of our standard permit set. Not every lot suits two stories given Westchester’s typical 5,000-7,500 sq ft dimensions and rear yard coverage limits. Call (213) 329-7167 and we’ll verify your specific lot’s feasibility during the free estimate.
Ready to price your project? Call (213) 329-7167 to schedule your free estimate. You’ll receive a written, itemized quote before any work begins - that’s Haven Standard, Clause 1, and it’s how we’ve operated since 2015.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Westchester since our founding in 2015.