Trusted Junior ADU & Interior Conversion for Santa Clarita Homeowners
A Santa Clarita Junior ADU & Interior Conversion typically runs $85,000-$175,000 all-in, from the first site measurement through final inspection, depending on whether you’re converting existing square footage or building an attached addition. Ellery ADU Studio has designed, permitted, and built over 900 ADUs since 2015, the year California’s ADU laws began their major shift, and every project has started with a written price before any work began. Call (747) 294-4817 to schedule your free estimate, or bring us any written estimate you already have for a Free Second Opinion.
Homeowners in Santa Clarita who bought between 2015 and 2025 are sitting on some of the highest price-per-square-foot purchases in the valley’s history. A Junior ADU, or JADU, lets you carve out a self-contained rental unit within your existing home, up to 500 square feet, with a separate entrance and its own kitchenette. An interior conversion, the broader category, covers everything from basement ADUs to above-garage units to attached additions that expand your footprint. What derails most projects in Santa Clarita isn’t the construction. It’s the gap between the designer who drew the plans and the builder who claims those plans were “value-engineered” halfway through. Ellery ADU Studio operates under one contract, one written price, and one standard: The Haven Standard. Nadia Ellery built this studio specifically to eliminate that designer-versus-builder blame gap. When the permit set, the construction documents, and the build crew all answer to the same contract, there’s nowhere for accountability to hide.
What Our Junior ADU & Interior Conversion Service Includes
Basement ADU
A basement ADU converts your below-grade square footage into a permitted, rentable unit with its own kitchenette, bathroom, sleeping area, and separate entrance. In Santa Clarita, we see this most often in the older hillside homes of Canyon Country and Sand Canyon, where basements were built for storage but sit on stable, dry ground that can support residential occupancy. Ellery ADU Studio measures ceiling height, egress window requirements, and moisture conditions during the first site visit, then produces a permit set that addresses the specific Santa Clarita Valley floor-area-ratio calculations that apply to below-grade space. We’ve converted basements that added $1,200-$1,800 in monthly rental income for homeowners in the Castaic and Santa Clarita area.
Above-Garage ADU
An above-garage ADU, sometimes called a carriage house or garage-top unit, builds a new residential floor over your existing garage structure. This works when the garage foundation and framing can handle the additional load, or when we’re replacing the garage entirely and engineering the new structure for residential use. In Santa Clarita’s flatter neighborhoods like Valencia and Saugus, where lot coverage rules are tighter than in the hills, going vertical preserves your yard space while adding 400-500 square feet of rental-grade living space. Ellery ADU Studio produces structural calculations as part of the permit set, not as a change order six weeks in. We coordinate with Santa Clarita’s building department on the specific seismic bracing requirements that apply to second-story additions in this zone.
Room-to-ADU Conversion
A room-to-ADU conversion takes an existing bedroom, den, or attached in-law space and reconfigures it as a Junior ADU with a kitchenette, private bathroom, and exterior door. This is the fastest path to rental income in Santa Clarita, often completing in 4-6 months from permit application to final inspection, because the footprint already exists. We see this frequently in the 1970s-1990s tract homes of Newhall and Valencia, where a ground-floor master suite or large bonus room sits adjacent to an exterior wall. Ellery ADU Studio verifies that the existing space meets JADU requirements: owner occupancy in the main dwelling, separate exterior access, and either its own bathroom or shared bathroom access with an interior door lock. The permit set documents every existing condition so the city inspector can verify code compliance without guesswork.
Attached Addition ADU
An attached addition ADU extends your home’s footprint with new construction that creates a separate, self-contained unit sharing at least one wall with the main house. Unlike a JADU, this can exceed 500 square feet and does not require owner occupancy in the main dwelling, making it suitable for homeowners who want to rent both units or eventually move into the ADU themselves. In Santa Clarita, we design these to match existing rooflines and siding profiles, particularly in neighborhoods with active HOAs in Stevenson Ranch or Westridge. Ellery ADU Studio produces the full permit set, including Title 24 energy calculations and Santa Clarita’s specific setback and height compliance documentation, before construction begins. The written price covers drawings, permits, and build; no separate architect invoice appears later.
Interior JADU
An interior JADU is the most constrained but often most cost-effective conversion: up to 500 square feet within your existing walls, with efficiency kitchen, sleeping area, and separate entrance, while you remain in residence. The California Housing and Community Development department sets the baseline rules, but Santa Clarita applies its own fire separation and utility metering interpretations that catch unprepared applicants. Ellery ADU Studio has navigated these specific local requirements since 2015, when the first wave of state ADU legislation took effect. We document the existing electrical panel capacity, water heater location, and HVAC zoning in the permit set so the city can verify compliance without multiple rounds of corrections. For homeowners in Santa Clarita’s older neighborhoods like Old Town Newhall, where electrical service may be 100 amps, we specify the panel upgrade path in the initial written price if needed.
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 that can integrate with interior conversions and attached additions where structural or envelope components need replacement. With Cover, we’ve incorporated their precision-engineered wall and roof systems into above-garage ADUs in Santa Clarita where the existing garage structure required complete rebuild rather than retrofit. Their panelized approach reduces weather exposure during construction, which matters during Santa Clarita’s brief but intense winter rain periods. We’ve also specified Dvele’s fully integrated electrical and mechanical chase systems for attached addition ADUs where the homeowner wanted factory-built quality with site-built flexibility. Dvele’s pre-wired wall panels reduce the subcontractor coordination that typically delays interior conversion projects by two to four weeks.
Mighty Buildings’ 3D-printed polymer composite panels have allowed us to create above-garage ADUs in Santa Clarita with complex geometries that would require expensive custom framing on site. Their fire-resistant material meets California’s stringent wildfire-urban interface requirements, which apply to portions of Canyon Country and Sand Canyon. For Boxabl’s fold-out room modules, we’ve integrated their Casita units into larger attached addition projects where the homeowner wanted a bedroom-bathroom core delivered complete, then wrapped with site-built living and kitchen space to match the existing home. Whether you have one of these systems specified already, or you’re comparing modular against stick-built for your Santa Clarita conversion, we can evaluate the integration path and quote it in writing.
Signs You Need Junior ADU & Interior Conversion Right Now
- Your mortgage payment has outpaced your income growth. Santa Clarita homeowners who bought at 2020-2022 peaks are carrying monthly payments $800-$1,500 above current rental rates for comparable properties. A JADU generating $1,200-$1,800 monthly can restructure your housing cost equation without selling into a down market. Ellery ADU Studio can measure your existing space and deliver a written price within two weeks.
- You have an adult child or aging parent who needs proximity, not dependence. The “boomerang” adult child and the “sandwich generation” caregiver are both common profiles in Santa Clarita’s 32-50 homeowner demographic. A room-to-ADU conversion creates separate households with shared property costs, preserving relationships that shared kitchens often strain. We’ve completed conversions for both scenarios in Valencia and Stevenson Ranch.
- Your garage, basement, or bonus room sits unused 350+ days per year. Storage is the default use for underutilized square footage, but at Santa Clarita’s price per square foot, that’s an expensive closet. If the space has exterior wall access, adequate ceiling height, and reasonable structural condition, it’s likely convertible. Our site visit documents all three conditions with photos you receive.
- You’re considering selling but would lock in a significant capital loss. Selling a home bought at peak pricing means realizing that loss permanently. Adding rental income through a JADU or interior conversion changes the property’s cash flow profile, making it holdable until market recovery. We’ve advised Santa Clarita homeowners through this specific financial calculation since 2015.
- Your HOA or city has recently liberalized ADU rules. Santa Clarita updated its ADU ordinance in response to state legislation, and many HOAs in planned communities like Valencia and Westridge have followed with amended CC&Rs. The window for conversion may be wider now than when you purchased. We track these changes and can confirm your specific property’s eligibility during the free estimate visit.
Our Junior ADU & Interior Conversion Process - Step by Step
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Site Measurement & Feasibility Documentation. Nadia Ellery or a senior designer visits your Santa Clarita property with a laser measure, moisture meter, and structural assessment tools. We photograph every existing condition, measure ceiling heights and window openings, and verify electrical panel capacity and water heater location. You receive these photos with annotated notes within 48 hours, per Haven Standard Clause 3 (Documented Photo Record).
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Written Price & Scope Lock. Within 10 business days, you receive a single written price covering design, permit set preparation, city submittal, and construction. Haven Standard Clause 1 requires this price before any work begins. The scope is itemized by trade: demolition, framing, electrical, plumbing, HVAC, finishes, and final inspection coordination. Under Clause 5 (No Surprises), this scope locks at contract signing. No door-side upsells, no scope creep.
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Permit Set Production & City Submittal. Our in-house designers produce construction documents to Santa Clarita’s specific plan check requirements, including Title 24 energy compliance, structural calculations for any new framing, and fire separation details for JADUs. We submit electronically through the city’s portal and manage all correction responses. The average Santa Clarita interior conversion permit takes 6-10 weeks for approval, depending on complexity and plan check backlog.
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Construction with Weekly Photo Documentation. Our background-checked, uniformed crews work from the permitted drawings, not field decisions. Every visit produces dated, geotagged photos of work completed and conditions found, uploaded to your project portal. If we discover asbestos in a 1970s ceiling texture or inadequate joist spacing in an above-garage project, we document it, explain the implication, and provide a written change order only if the scope genuinely expands beyond the permitted drawings.
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Final Inspection & 365-Day Done Right Promise. We coordinate all inspections, from rough electrical and plumbing to final occupancy. Once the certificate of occupancy issues, your 365-Day Done Right Promise takes effect: if any element of the finished ADU is not built to the permitted drawings, Ellery ADU Studio makes it right, in writing, with no deductible or service fee. This is Haven Standard Clause 7, and it’s binding on us from day one.
How Much Does Junior ADU & Interior Conversion Cost in Santa Clarita?
A typical room-to-ADU or interior JADU conversion in Santa Clarita runs $85,000-$125,000 all-in, from first measurement through final inspection. Above-garage ADUs, which require structural engineering and often complete roof replacement, typically range $120,000-$175,000. Basement ADUs fall between $95,000-$140,000 depending on ceiling height modification needs and egress window installation. Attached addition ADUs, which expand your footprint with new foundation and framing, generally start at $150,000 and can reach $220,000 for larger units with high-end finishes.
What moves you within these ranges? Three factors dominate Santa Clarita pricing. First, existing conditions: a 100-amp electrical panel requiring upgrade to 200 amps adds $4,000-$7,000. A slab-on-grade garage that needs stem-wall foundation work for second-story load adds $8,000-$15,000. Second, utility separation: Santa Clarita requires separate electric metering for most ADUs over JADU size, and gas or water separation adds line items that vary by distance to the main. Third, finish level: rental-grade finishes with durable materials run lower than owner-occupant specifications with custom cabinetry or premium flooring.
How to avoid overpaying? Get the permit set quality specified in writing. Low bids often come from contractors who treat drawings as the homeowner’s responsibility, then charge change orders when the city rejects substandard plans. At Ellery ADU Studio, the permit set is the core product, included in the single written price, produced by designers who understand Santa Clarita’s specific interpretation of state ADU law. We’ve seen competitors’ “budget” conversions stall for months in plan check because the designer and builder pointed at each other.
Every free estimate includes a line-item breakdown of these factors for your specific property. No deposit, no commitment. Call (747) 294-4817 to schedule.
Junior ADU & Interior Conversion Near Santa Clarita - Our Service Area
Ellery ADU Studio serves Santa Clarita directly, with typical initial site visits available within 3-5 business days of your call. Our primary service radius includes Junior ADU & Interior Conversion in Stevenson Ranch, where HOA coordination is often the critical path, and Junior ADU & Interior Conversion in Sylmar, where hillside grading and access shape project feasibility. We also regularly work in Castaic, Granada Hills, Porter Ranch, Mission Hills, Northridge, Chatsworth, Panorama City, Winnetka, and San Fernando. Each city applies California’s baseline ADU law with local amendments, and our permit sets are customized to each jurisdiction’s specific plan check requirements. If you’re unsure whether your property falls within our service area, call (747) 294-4817 and we’ll confirm based on your address.
Serving Santa Clarita, CA - Our Local Coverage Area
We’re based in the Santa Clarita 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 Santa Clarita
A Junior ADU, or JADU, is a self-contained living unit of up to 500 square feet created within your existing home, with a separate entrance, efficiency kitchen, and either its own bathroom or shared bathroom access. An interior conversion is the broader category that includes JADUs plus basement ADUs, above-garage ADUs, room conversions, and attached additions that create new rental units from existing or expanded square footage. Ellery ADU Studio handles all types under one contract with one written price. Call (747) 294-4817 for a free estimate on your specific property.
Most interior JADU conversions in Santa Clarita take 4-6 months from permit application to final inspection, while above-garage and attached addition ADUs typically run 6-9 months. Permit processing accounts for 6-10 weeks of that timeline, with construction duration depending on existing conditions and finish complexity. Ellery ADU Studio’s design-build model compresses the typical designer-to-builder handoff delay by 3-4 weeks. For a timeline specific to your property, call (747) 294-4817.
Interior JADU conversions in Santa Clarita typically run $85,000-$125,000 all-in, above-garage ADUs $120,000-$175,000, and attached additions $150,000-$220,000 depending on structural requirements and finish level. Every Ellery ADU Studio project receives a written price before any work begins, per Haven Standard Clause 1, with no “call for a quote” opacity. Call (747) 294-4817 for an exact quote on your property - estimates are free.
Yes, Ellery ADU Studio specifies and coordinates Cover, Dvele, Mighty Buildings, and Boxabl systems where their components integrate efficiently with interior or attached-addition projects. Cover’s panelized walls work well for above-garage rebuilds, while Dvele’s pre-wired systems reduce electrical subcontractor coordination in room conversions. We evaluate brand fit during the feasibility phase and quote integration in the written price if appropriate. Call (747) 294-4817 to discuss whether prefab integration makes sense for your Santa Clarita property.
Yes, and we offer a Free Second Opinion on any written estimate or permit set already in hand. We frequently review competitors’ drawings for Santa Clarita homeowners who discovered that their “complete” permit set was missing Title 24 calculations, structural details, or Santa Clarita-specific setback verifications. If the set is buildable, we’ll quote construction from it. If it’s deficient, we’ll explain exactly what’s missing and what it would cost to complete. Call (747) 294-4817 to schedule a review.
Every project is backed by our 365-Day Done Right Promise: if the finished ADU is not built to the permitted drawings, Ellery ADU Studio makes it right at no additional cost. This is Haven Standard Clause 7, agreed in writing before construction starts, not a verbal assurance. Beyond the one-year promise, individual trades carry manufacturer warranties on materials, and our workmanship on structural, electrical, and plumbing systems is documented in your final project binder. Call (747) 294-4817 for warranty details specific to your project type.
Gather your property’s original floor plans if available, a recent utility bill showing your electrical service size, and any HOA correspondence about ADU rules. We’ll need access to the space being considered for conversion, your electrical panel, and your water heater location. No cleaning or preparation of the space is necessary; we’re assessing structure and systems, not decor. The visit takes 45-90 minutes, and you’ll receive your written price within 10 business days. Call (747) 294-4817 to schedule.
Schedule Your Junior ADU & Interior Conversion Service in Santa Clarita Today
Call (747) 294-4817 to schedule your free estimate. A live person answers 24/7, and you’ll receive a written price before any work begins, per Haven Standard Clause 1. Bring any existing estimate for a Free Second Opinion. Nadia Ellery and the team at Ellery ADU Studio have served Santa Clarita since 2015, and we’ll document every condition, specify every material, and warrant every detail in writing.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Santa Clarita since 2015.