Trusted Junior ADU & Interior Conversion for Chino Hills Homeowners
A Chino Hills Junior ADU & Interior Conversion typically runs $85,000-$165,000 all-in, from the first measured drawing through final inspection, depending on whether you’re converting existing square footage or building an attached addition. Most projects we take on in Chino Hills move from signed contract to permit submission in 4-6 weeks, with construction lasting 3-5 months for interior work and 5-8 months for attached additions. Call (951) 456-4467 and we’ll schedule a site visit with a written price before any work starts.
Since 2015, Ellery ADU Studio has designed, permitted, and built over 900 ADUs across California’s inland corridor. We’re not a contractor who dabbles in drawings, or a designer who disappears once the permit is pulled. We hold the design-build contract ourselves: one written price, one accountable party, and a 365-Day Done Right Promise backed in writing under The Haven Standard. In Chino Hills specifically, we’ve worked through the city’s particular requirements for hillside grading, fire access in the Canyon Hills and Vellano areas, and the utility coordination headaches that come with older homes in the older central neighborhoods near Chino Avenue. Nadia Ellery founded the studio the same year California’s ADU laws began their major shift, and we’ve tracked every subsequent code change since.
What Our Junior ADU & Interior Conversion Service Includes
Basement ADU
A Basement ADU converts below-grade space into a permitted, habitable dwelling unit with its own kitchen, bathroom, sleeping area, and separate exterior entrance. In Chino Hills, this makes sense for homes built into hillsides, particularly in the western canyon areas where basements are more common and the slope creates natural daylight opportunities through walk-out entries. We assess ceiling height, ventilation requirements per the California Residential Code, and moisture barriers before quoting. Our permit set includes the egress window sizing, the mechanical ventilation plan for habitable basements, and the fire separation details that Chino Hills Building & Safety reviews closely.
Above-Garage ADU
An Above-Garage ADU adds a second story over an existing or expanded garage structure, creating a detached or attached dwelling unit depending on your property configuration. This works well in Chino Hills neighborhoods like Butterfield Ranch and Oak Tree Downs, where flat lots and standard garage footprints make structural stacking feasible. We evaluate the existing foundation’s load capacity, design the stair or exterior access route, and coordinate the utility separations. Our drawings specify the lateral bracing for Chino Hills’ seismic zone, and we handle the structural calculations in-house rather than outsourcing them to a separate engineer.
Room-to-ADU Conversion
A Room-to-ADU Conversion transforms an existing bedroom wing, in-law suite, or oversized bonus room into a fully permitted Junior ADU with kitchenette and private bathroom. This is the fastest path to rental income in Chino Hills, often completing in 3-4 months, because the envelope already exists. We verify that the space meets minimum square footage requirements, design the kitchenette layout around existing plumbing stacks where possible, and document the fire-rated separation from the primary residence. Our permit set includes the electrical load calculations showing that your panel can handle the additional circuits, or we specify the subpanel upgrade if needed.
Attached Addition ADU
An Attached Addition ADU extends the primary residence with new construction that creates a separate dwelling unit sharing one wall. In Chino Hills, this suits homeowners who want to keep the unit connected for family use or who lack the setback space for a fully detached structure. We design the addition to match your existing roofline and exterior materials, specify the one-hour fire-rated wall assembly between units, and navigate the side-yard setback requirements that vary by your specific zoning. Our single contract covers the architectural drawings, structural plans, MEP coordination, and construction, so there’s no gap between what was designed and what gets built.
Interior JADU
An Interior JADU, or Junior Accessory Dwelling Unit, is a specific California classification: a unit of 500 square feet or less contained entirely within the walls of the existing primary residence, with an efficiency kitchen and exterior access. Chino Hills allows these by-right on single-family lots, and they’re often the most cost-effective way to add rental income or house a family member. We identify the best candidate space, design the efficiency kitchen to code, and ensure the separate exterior door meets egress requirements. Our permit set documents the owner-occupancy requirement that comes with JADU classification, and we explain the implications for your property tax assessment before you sign.
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 Specify and Coordinate for Junior ADU & Interior Conversion
Ellery ADU Studio specifies and coordinates prefab and modular systems from James Hardie, Abodu, Cover, and Dvele within the same single-contract structure. For interior conversions and attached additions in Chino Hills, we often use James Hardie fiber-cement siding and trim to match existing exteriors, particularly in the newer developments where builders originally specified Hardie products. We maintain direct supplier relationships and can source matching profiles without the guesswork that delays other projects. For clients considering a hybrid approach, an Abodu unit as a detached companion to an interior conversion lets you maximize rental density on a single lot, and we coordinate both scopes under one written price and one permit timeline.
Whether your project involves Abodu, Cover, Dvele, James Hardie, or any conventional stick-built assembly, we design to the system’s specifications rather than forcing a generic solution. Our permit sets include the manufacturer’s structural details, the fire-resistance ratings, and the installation sequences that Chino Hills Building & Safety expects to see. If you’re comparing estimates that mention these brands without showing the corresponding documentation, we offer a Free Second Opinion on any written estimate already in hand.
Before
AfterSigns You Need Junior ADU & Interior Conversion Right Now
- Your adult child has moved back home and needs independent space. The “boomerang” pattern is common in Chino Hills, where high entry-level home prices keep younger adults in the family home longer. A JADU or room conversion creates privacy without the cost of a second mortgage, and the rental income you forgo from a market tenant is replaced by household stability.
- You’re carrying a mortgage rate above 5.5% and need supplemental income. Homeowners who bought or refinanced between 2015 and 2022 in Chino Hills are seeing their total housing cost eat into savings. A permitted ADU generates $1,800-$2,800 monthly in this market, turning dormant square footage into a revenue stream that the lender recognizes for qualification purposes.
- Your aging parent needs proximity, not dependence. The “granny flat” origin of ADU law still drives many conversions. A room-to-ADU or basement ADU lets you provide care without sacrificing your household’s routines, and the separate address supports Medicaid and VA benefit applications that require independent living documentation.
- You’ve received a notice from the city about unpermitted living space. Chino Hills Code Enforcement periodically identifies garage conversions or bonus rooms used as dwellings without permits. The path to compliance is a retroactive permit set, which we prepare from as-built measurements, or a full conversion to meet current code. Either way, the unpermitted use stops the clock on fines and liability.
- Your property tax assessment hasn’t captured the ADU potential. Under California’s Prop 13 framework, adding a JADU typically triggers only a supplemental assessment on the new construction value, not a full reset. The window to build at current cost bases narrows as material and labor inflation continues. Permitting now locks in your tax treatment before further reassessment cycles.
Our Junior ADU & Interior Conversion Process - Step by Step
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Site Visit and Feasibility Assessment. We measure your existing space, photograph conditions, and check setback, height, and coverage against Chino Hills Municipal Code. You receive a documented photo record of what we found, not a summary of how it felt. Within 48 hours, we deliver a written feasibility memo with a preliminary dollar range.
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Design Development and Permit Set Preparation. Our architects produce the full construction documents: floor plans, elevations, structural calculations, MEP plans, and the Title 24 energy compliance package. For Chino Hills, we include the specific fire department access details that the city requires for hillside zones. The permit set is the core product, not an afterthought.
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Fixed-Price Contract Under The Haven Standard. We present a written price before any work starts, per Haven Standard Clause 1. The scope is locked at signing under Clause 5 (No Surprises): no door-side upsells, no scope creep, no “we found an issue” calls that add 20% to the total. You know the full cost before you commit.
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Permit Submission and City Coordination. We submit to Chino Hills Building & Safety and manage all plan-check corrections. Our familiarity with the city’s reviewers, particularly on hillside grading and utility tie-in questions, shortens this phase compared to first-time filers. We don’t start construction until permits are in hand.
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Construction, Inspection, and Final Documentation. Our background-checked, uniformed crews build to the permitted drawings. Every site visit generates a documented photo record that you receive. Final inspection passed, certificate of occupancy issued, and the 365-Day Done Right Promise begins. If the finished ADU is not built to the permitted drawings, we make it right, in writing, before the project starts.
How Much Does Junior ADU & Interior Conversion Cost in Chino Hills?
A typical Interior JADU in Chino Hills runs $85,000-$125,000 all-in, from measured drawings through final inspection. A Room-to-ADU Conversion with existing bathroom access falls at the lower end; a Basement ADU with new egress windows, mechanical ventilation, and moisture remediation falls at the higher end. An Attached Addition ADU typically runs $140,000-$195,000 depending on square footage and foundation requirements. Above-Garage ADUs range $125,000-$165,000, with the structural upgrade to the existing garage foundation as the largest variable.
| Project Type | Typical Range in Chino Hills | Primary Cost Drivers |
|---|---|---|
| Interior JADU | $85,000-$125,000 | Kitchenette scope, electrical panel capacity, exterior door location |
| Room-to-ADU Conversion | $90,000-$130,000 | Bathroom addition, plumbing rerouting, fire separation |
| Basement ADU | $110,000-$165,000 | Ceiling height, egress windows, moisture barrier, ventilation |
| Above-Garage ADU | $125,000-$165,000 | Foundation reinforcement, stair access, utility routing |
| Attached Addition ADU | $140,000-$195,000 | Square footage, foundation type, roof tie-in complexity |
What moves you within these ranges? Three factors: the condition of existing utilities (a 100-amp panel needs upgrading, a 200-amp panel may not), the accessibility for material delivery (steep driveways in Canyon Hills add labor hours), and the finish level you select. We quote each line item separately in our written estimate, so you see where the money goes before you sign. To avoid overpaying, get a second opinion on any estimate already in hand, ours is free. Call (951) 456-4467 for an exact quote on your specific property.
Junior ADU & Interior Conversion Near Chino Hills - Our Service Area
We design, permit, and build Junior ADUs and Interior Conversions throughout the Chino Hills sphere and surrounding cities: Chino, Yorba Linda, Anaheim, Diamond Bar, Pomona, Eastvale, Montclair, Ontario, Rowland Heights, Corona, and Upland. Typical response time for a site visit in Chino Hills proper is 2-3 business days; for Corona or Eastvale, 3-4 days. We’ve worked with Chino Hills’ Building & Safety department specifically on hillside grading plans, fire access in the Vellano and Canyon Hills areas, and the utility coordination that comes with older homes near the original town center. That familiarity shortens permit timelines compared to firms that file here occasionally.
Serving Chino Hills, CA - Our Local Coverage Area
We’re based in the Chino Hills 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 Chino Hills
Our Junior ADU & Interior Conversion in Pomona follows the same approach: the transformation of existing interior space within a single-family home into a separate, permitted dwelling unit, or the addition of new attached square footage for the same purpose. In Chino Hills, this includes JADUs (500 sq ft max, within existing walls), room conversions, basement ADUs, and attached additions. Ellery ADU Studio handles the architectural drawings, structural engineering, permit submission, and construction under one contract at one written price. Call (951) 456-4467 to discuss which type fits your property.
Most Interior JADUs and Room-to-ADU Conversions in Chino Hills take 3-5 months from signed contract to certificate of occupancy, with permit processing adding 6-10 weeks. Basement ADUs and Attached Addition ADUs typically run 5-8 months due to structural and utility complexity. Our permit set preparation is the pacing item we control; Chino Hills Building & Safety’s plan-check timeline varies seasonally. We don’t start construction until permits are in hand, so the schedule we quote is the schedule you get.
Interior JADUs in Chino Hills typically run $85,000-$125,000 all-in; Attached Addition ADUs run $140,000-$195,000. The exact figure depends on your existing conditions, the scope of kitchen and bathroom work, and any structural or utility upgrades needed. Every Ellery ADU Studio project is quoted with a written price before any work starts, per Haven Standard Clause 1. Call (951) 456-4467 for a site visit and exact quote on your property.
We specify and coordinate Abodu, Cover, Dvele, and James Hardie systems within our single-contract model, though prefab brands are more commonly used for detached ADUs than interior conversions. For attached additions and above-garage ADUs, we may integrate a modular unit or use conventional framing with James Hardie exterior finishes to match existing materials. We design to the manufacturer’s specifications and include their details in the permit set. If your estimate mentions a brand without showing the corresponding documentation, bring it in for a Free Second Opinion.
Junior ADU & Interior Conversion is planned construction, not emergency repair, so we do not offer same-day dispatch. A live person answers our phones 24/7 to schedule site visits and answer questions about active projects. If you have an urgent safety issue, such as a structural concern or gas leak during construction, we have protocols to address it within hours. For planned projects, we book site visits within 2-3 business days in Chino Hills.
Every project carries our 365-Day Done Right Promise: if the finished ADU is not built to the permitted drawings, we make it right, backed in writing before construction starts. This covers workmanship, material installation, and compliance with the approved plans. Manufacturer warranties on appliances, fixtures, and specified products run separately and are transferred to you at completion. The Haven Standard documentation you receive spells out exactly what is covered and for how long.
Gather your property’s legal description or recent tax bill, any previous architectural drawings, and a rough idea of your budget range. We measure everything ourselves, so you don’t need to prepare dimensions. If you’ve received estimates from other firms, bring them for our Free Second Opinion. We’ll photograph conditions, check zoning constraints, and deliver a written feasibility memo with a preliminary price range within 48 hours. Call (951) 456-4467 to schedule.
Schedule Your Junior ADU & Interior Conversion Service in Chino Hills Today
Call (951) 456-4467 to schedule your free site visit. A live person will answer, 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 in writing. No voicemail queue, no callback that doesn’t materialize, no obligation until you see the full scope and cost. Nadia Ellery and the team at Ellery ADU Studio have served Chino Hills since 2015.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Chino Hills since 2015.