Trusted Junior ADU & Interior Conversion for Westchester Homeowners
A Junior ADU & Interior Conversion in Westchester typically runs $85,000-$175,000 all-in, from the first measured drawing through final inspection, and most projects reach permit approval within 8-14 weeks. Ellery ADU Studio has designed, permitted, and built 900+ ADUs since 2015, the year California’s statewide ADU laws shifted, and every project has started with a written price under Haven Standard Clause 1. If you’re sitting on an underused basement near LAX, a room above a garage in the Kentwood area, or a spare bedroom off Manchester Boulevard, converting it to a permitted Junior ADU is one of the few ways to add rental income without adding square footage to your roofline. Call (213) 698-7591 to schedule your free estimate. Our live-answer line is open 24/7.
What Our Junior ADU & Interior Conversion Service Includes
Basement ADU
A basement ADU converts an existing below-grade space into a self-contained dwelling unit with its own kitchen, bathroom, sleeping area, and separate exterior entrance. In Westchester, we see this most often in 1940s-1960s homes near Loyola Marymount’s perimeter, where full basements were built for storage but sit unused while mortgage payments climb. Ellery ADU Studio Westchester measures ceiling height against LA City code, specifies moisture-barrier and ventilation systems for the marine layer that rolls in off Dockweiler Beach, and produces a permit set that addresses egress window requirements before the city asks. The drawings, the structural calcs, and the construction contract are one document at one written price.
Above-Garage ADU
An above-garage ADU, sometimes called a carriage house conversion, transforms the second story of an existing garage into a dwelling unit while the ground level remains parking, storage, or workshop space. This works well on Westchester’s narrower lots where setback rules prevent building outward, particularly in the Chesterfield Square-adjacent blocks where lot coverage is already tight. We evaluate the existing foundation and framing for live-load capacity, design a staircase or exterior access that meets LA Fire Department egress requirements, and coordinate the utility separations that let you meter water and electric independently. The permit set includes structural engineering stamped for the additional weight of a kitchen and occupant load.
Room-to-ADU Conversion
A room-to-ADU conversion takes an existing bedroom, den, or attached living space and reconfigures it as a Junior ADU with efficiency kitchen and separate entrance. This is the fastest path to rental income for Westchester homeowners who don’t have a basement or garage to work with, and it’s common in the single-story ranch homes east of Sepulveda Boulevard. We verify that the proposed unit meets Junior ADU size limits, currently 500 square feet maximum under California state law, and we document the owner-occupancy requirement that applies to the primary residence. Our permit set includes the fire-rated separation between units and the independent utility shutoffs that LA Building requires.
Attached Addition ADU
An attached addition ADU extends the primary residence with new construction that creates a separate dwelling unit sharing at least one wall. In Westchester, this suits homeowners who need more than 500 square feet or who want a full kitchen rather than the efficiency kitchen a Junior ADU allows. We model the addition to match existing rooflines where possible, specify James Hardie siding or another finish that blends with the neighborhood character, and engineer the foundation tie-in to the existing slab. The Haven Standard Clause 5 (No Surprises) locks the scope at signing, so the price you receive before work starts is the price you pay at final inspection.
Interior JADU
An Interior JADU, or Junior Accessory Dwelling Unit, is the most restricted and most affordable conversion type: maximum 500 square feet, contained entirely within the walls of the existing primary residence, with an efficiency kitchen and separate exterior access. Westchester homeowners near Playa del Rey and the airport corridor use these for aging parents or as Airbnb-compliant short-term rentals. We identify the optimal room configuration for natural light and ventilation requirements, design the minimal plumbing and electrical branch circuits to keep costs down, and produce a permit set that satisfies both LA City Planning and LA Building. Because the work is interior-only, weather delays are eliminated and inspection scheduling is more predictable.
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.
Brands We Service for Junior ADU & Interior Conversion
Ellery ADU Studio specifies and coordinates prefab and modular systems from Mighty Buildings, Boxabl, and Plant Prefab for clients who want factory-built precision integrated into their conversion project. With Mighty Buildings, we’ve completed interior fit-outs where the 3D-printed wall panels arrived with MEP rough-in already embedded, cutting field time by weeks on a Kentwood basement conversion in 2023. Boxabl’s Casita units require precise foundation prep and utility stub-outs that we engineer into the permit set before the module ships, avoiding the change orders that plague site-built-meets-prefab projects. Plant Prefab’s custom panelized systems let us match existing roof pitches and siding profiles on attached additions, so the new unit reads as original construction rather than an afterthought.
Whether your project involves Tuff Shed structures for ancillary storage that must be relocated before conversion, James Hardie siding to match a 1950s Westchester original, or any other manufacturer, we can help. Our design-build model means we specify the products, draw the details, and build to those drawings under a single contract. No finger-pointing between designer and builder when a panel doesn’t fit or a finish doesn’t match.
Signs You Need Junior ADU & Interior Conversion Right Now
- Your mortgage payment has outpaced your income growth. Westchester home prices rose sharply between 2015 and 2022, and many buyers who stretched to purchase are now carrying payments that consume 40% or more of monthly income. A permitted Junior ADU generating $1,500-$2,200 in monthly rent changes the math without selling the asset.
- You have a basement, garage upper level, or spare room that stores nothing but clutter. The space is already built, already roofed, already on your property tax bill. Every month it sits unused is a month of forgone rental income and deductible depreciation you didn’t claim.
- A family member needs independent living nearby. Aging parents, adult children returning from school, or a sibling in transition need privacy the main house doesn’t provide. A Junior ADU keeps family close without the friction of shared bathrooms and kitchen schedules.
- Your property tax assessment jumped after a recent sale or refinance. California’s Proposition 19 and market resets have increased tax burdens for recent Westchester buyers. Rental income from a legal ADU offsets the new assessment and builds equity in an asset you already own.
- LA City has flagged an unpermitted unit during a sale or inspection. Unpermitted conversions discovered during escrow kill deals and trigger costly retrofits under duress. A permitted, code-compliant Junior ADU protects your sale price and insurability, and the permit history follows the property, not the owner.
Our Junior ADU & Interior Conversion Process - Step by Step
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Site Measure and Zoning Review. We visit your Westchester property with laser measure and camera, document existing conditions with a photo record you receive same-day, and verify your lot’s zoning designation against LA City ADU ordinances. This includes setback measurements, height district classification, and any Historic Preservation Overlay Zone restrictions that apply in pockets of Westchester.
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Conceptual Design and Written Price. Within two weeks, you receive schematic floor plans, a 3D massing model, and a line-item written quote. Haven Standard Clause 1 requires this price before any work begins. The quote breaks out design and permitting, construction, and any site-specific contingencies like asbestos abatement or foundation reinforcement.
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Permit Set Production and Submission. Our architectural team produces the full construction document set: plans, elevations, sections, structural calculations, Title 24 energy compliance, and green building checklist. We submit to LA Department of Building and Safety and manage plan-check corrections without additional fees.
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Construction with Documented Photo Record. Our background-checked, uniformed crews build to the permitted drawings, and every site visit generates dated photos of work-in-place. You receive these through a shared folder, so you see the moisture barrier behind the drywall and the fire-rated separation between units, not just a summary of how the week went.
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Final Inspection and 365-Day Done Right Promise. We coordinate all inspections, correct any punch-list items, and deliver keys with a written warranty. If the finished ADU is not built to the permitted drawings, we make it right, in writing, before the project starts and for 365 days after completion.
How Much Does Junior ADU & Interior Conversion Cost in Westchester?
A typical Interior JADU in Westchester runs $85,000-$125,000 all-in, from measured drawings through final inspection. A basement ADU with moisture mitigation and egress window cutting typically falls between $110,000 and $155,000. Above-garage ADUs, which often require structural reinforcement of the existing garage foundation, range from $130,000 to $175,000. Room-to-ADU conversions at grade level, where utility access is simplest, usually land in the $90,000-$130,000 range. Attached additions, because they involve new foundation work and roof tie-ins, start around $140,000 and can reach $200,000 depending on square footage and finish level.
What moves the number: existing ceiling height (basements under 7 feet 6 inches require excavation or dropped floors), the condition of existing electrical service (100-amp panels often need upgrading to 200-amp for a second unit), and the distance to sewer and water mains (a 40-foot trench across a Westchester backyard adds material and restoration costs). How to avoid overpaying: get a written line-item quote that separates design, permitting, and construction, and verify that the contractor carries the license number on every page, not just the homepage. A free estimate from Ellery ADU Studio Westchester includes all of this, and our Free Second Opinion applies to any written estimate already in your hand.
Junior ADU & Interior Conversion Near Westchester - Our Service Area
Ellery ADU Studio Westchester serves homeowners throughout the LAX corridor and Westside, including Junior ADU & Interior Conversion in Culver City, Junior ADU & Interior Conversion in Inglewood, and the broader Los Angeles area from Venice and Santa Monica east to Hawthorne and Gardena, north to Brentwood and Beverly Hills, and south to Redondo Beach. Most Westchester properties receive initial site visits within 48 hours of scheduling, and permit set delivery timelines are consistent across LA City jurisdiction boundaries. Whether you’re in the Kentwood flats, the Manchester corridor, or the hillside pockets near Loyola Marymount, the same design-build team and the same Haven Standard terms apply.
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.
Frequently Asked Questions - Junior ADU & Interior Conversion in Westchester
Our Junior ADU & Interior Conversion in Venice transforms existing interior space within a single-family home into a smaller, self-contained dwelling unit with its own entrance, efficiency kitchen, and bathroom. Unlike a full ADU, a Junior ADU is capped at 500 square feet, must be contained within the walls of the primary residence, and requires the owner to occupy either the main house or the Junior ADU. In Westchester, this typically means converting a basement room, a ground-floor bedroom, or a den off the main hallway into a rental-ready unit that meets LA City Building Code and California state ADU law.
Most Junior ADU & Interior Conversion projects in Westchester reach permit approval within 8-14 weeks, and our Junior ADU & Interior Conversion in Inglewood follows similar timelines and complete construction in 3-5 months, for a total timeline of 5-8 months from signed contract to certificate of occupancy. Basement ADUs with moisture mitigation or above-garage units with structural reinforcement extend toward the longer end. Room-to-ADU conversions at grade level, where no foundation work is required, often finish closer to 4 months total. Call (213) 698-7591 for a timeline estimate specific to your property - estimates are free.
Junior ADU & Interior Conversion costs in Westchester range from $85,000 for a simple Interior JADU to $175,000 for a complex above-garage unit with structural reinforcement, with most projects clustering between $100,000 and $140,000. The final number depends on existing conditions, code requirements for egress and fire separation, and finish selections. Every Ellery ADU Studio project receives a written price before work starts, per Haven Standard Clause 1, with no change orders for scope we’ve already drawn. Call (213) 698-7591 for an exact quote - estimates are free.
Yes. Ellery ADU Studio specifies and coordinates Mighty Buildings, Boxabl, and Plant Prefab systems within our single-contract design-build model, and we’ve integrated these factory-built components into both new detached and conversion-adjacent projects in Westchester and surrounding cities. Our permit sets include the foundation details, utility stub-outs, and structural connections that prefab manufacturers require but rarely provide for site-specific conditions. If you’re considering a prefab element for your conversion, we can evaluate whether it reduces cost or complexity in your specific case.
Junior ADU & Interior Conversion is planned construction, not emergency repair, so we do not advertise emergency dispatch or same-day construction starts. A live person answers our line 24/7 to schedule site visits, answer questions about active projects, or discuss a Free Second Opinion on a written estimate you’ve received elsewhere. For structural emergencies related to existing construction, we coordinate response through our licensed structural engineer. Call (213) 698-7591 to discuss your timeline - estimates are free.
Every Junior ADU & Interior Conversion is backed by our 365-Day Done Right Promise: if the finished unit is not built to the permitted drawings, Ellery makes it right, in writing, before the project starts. This covers workmanship, material installation, and compliance with the approved permit set. The promise is documented in your contract, not implied or verbal. For manufacturer warranties on fixtures, appliances, or prefab components, we pass through the full term and assist with any claims process.
Gather your property’s assessor parcel number, a recent utility bill showing your electrical service size, and any prior architectural drawings or surveys you have on hand. Clear access to the space being converted and to your electrical panel, and note any known issues like water intrusion, foundation cracks, or unpermitted prior work. We’ll measure, photograph, and research zoning during our site visit, so you don’t need to have answers ready. Call (213) 698-7591 to schedule - estimates are free, and a Free Second Opinion is available if you already have a written quote from another firm.
Schedule Your Junior ADU & Interior Conversion Service in Westchester Today
Call (213) 698-7591 to schedule your free estimate. A live person answers 24/7. 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 under The Haven Standard. Whether you’re converting a basement near LAX, a room above your garage in Kentwood, or a spare bedroom off Manchester Boulevard, Ellery ADU Studio Westchester handles the drawings, the permits, and the construction under one contract at one price. No designer-builder blame gap. No call-for-a-quote runaround. Just the scope, the number, and the documentation to back both.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Westchester since 2015.