Trusted Junior ADU & Interior Conversion for Pomona Homeowners
A Junior ADU & Interior Conversion in Pomona typically runs $85,000-$175,000 all-in, from measured drawings through final inspection, depending on whether you’re converting an existing room or building an attached addition. Most Pomona homeowners complete the full design-permit-build cycle in 8-14 months, with permit timelines driven by Los Angeles County’s ADU-specific review track. Ellery ADU Studio has designed, permitted, and built 900+ ADUs since 2015, every one with a written price before work started and a documented photo record when work was complete.
We’re not a contractor who outsources drawings. We’re a design-build studio, which means the same team that measures your existing space produces the permit set and manages construction. That matters in Pomona, where the Planning Department enforces California’s statewide ADU standards alongside local hillside overlay zones in neighborhoods north of Foothill Boulevard. When the designer and builder are the same entity, no one can point at the other when a setback or fire separation requirement changes your layout.
Call (657) 286-7915 to schedule your free estimate. A live person answers 24/7, and we offer a Free Second Opinion on any written estimate already in hand.
What Our Junior ADU & Interior Conversion Service Includes
Basement ADU
A basement ADU converts below-grade space into a permitted dwelling unit with its own kitchen, bathroom, sleeping area, and separate entrance. In Pomona, this works best for homes in the Ganesha Hills or Lincoln Park areas where basements were dug into the alluvial soil and have adequate ceiling height, typically 7 feet 6 inches minimum after finishes. We measure existing headroom, test for moisture intrusion, and produce a permit set that addresses Los Angeles County’s egress window requirements and ventilation standards. Our team has converted basements in Pomona’s older stock near downtown where original 1920s foundations require specific seismic anchoring details.
Above-Garage ADU
An above-garage ADU adds a new floor over an existing or replaced garage structure, creating a detached or attached unit depending on your lot configuration. This suits Pomona homeowners on the narrower 50-foot lots common south of the 10 Freeway, where setback rules prevent ground-level expansion. We evaluate the existing garage foundation for load capacity, design a structural package for the new floor, and coordinate the fire separation assembly between garage and living space. Our permit set includes the structural calculations Los Angeles County requires for this type of vertical addition, not just architectural drawings.
Room-to-ADU Conversion
A room-to-ADU conversion reconfigures existing interior space, typically a master suite, large bedroom, or unused den, into a self-contained Junior ADU with efficiency kitchen and separate exterior access. This is the fastest-permitting path in Pomona for homeowners who want rental income without new construction, often completing in 6-10 months. We verify that your existing floor area meets the 500-square-foot maximum for a Junior ADU under California Government Code Section 65852.22, design the kitchenette layout to code minimums, and ensure the separate entrance complies with Pomona’s emergency egress standards. Every conversion we design includes a fire-rated separation between the JADU and primary residence.
Attached Addition ADU
An attached addition ADU extends the primary residence with new construction that creates a separate dwelling unit sharing one wall. This fits Pomona lots where you have side or rear yard space but want to maintain the single-structure appearance preferred in neighborhoods like Phillips Ranch. We design the addition to match your existing roofline and exterior materials, produce full structural and MEP plans, and manage the California Energy Code compliance including Title 24 calculations. Our permit set addresses the fire separation between units, which Los Angeles County inspects at rough framing and final.
Interior JADU
An Interior JADU, or Junior Accessory Dwelling Unit, is the most compact permitted option: up to 500 square feet within the walls of your existing home, with an efficiency kitchen and exterior door. Pomona homeowners in the university district and near Cal Poly Pomona use these for graduate student rentals or aging parents. We identify the optimal room or rooms for conversion, verify that your lot allows a JADU under Pomona’s local implementation of state law, and produce a permit set that shows the required owner-occupancy covenant. Our drawings specify the separate electrical meter or sub-meter configuration you’ll need for legal rental.
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
We specify and coordinate prefab and modular systems from Plant Prefab and Boxabl for interior conversions where a factory-built module integrates with existing structure. Plant Prefab’s panelized system works well for attached additions in Pomona, where we can crane panels into a prepared opening and complete weathering in a single day. We’ve coordinated Boxabl’s compact casita units for above-garage installations where the module dimensions match the structural capacity of a reinforced garage foundation. Both brands require precise field measurements and a permit set that accounts for module connection details, which we produce in-house rather than delegating to the manufacturer.
We also specify James Hardie fiber-cement siding for exterior finishes on attached additions and above-garage units, matching Pomona’s aesthetic requirements in hillside overlay zones where wood-composite products face fire-risk restrictions. Whether your project involves Plant Prefab, Boxabl, James Hardie, or any other system, we coordinate material specifications within the same single contract that covers your permit set and construction. No separate purchase orders, no blame gap if the finish doesn’t align with the drawings.
Signs You Need Junior ADU & Interior Conversion Right Now
- Your mortgage payment has outpaced your income growth. Pomona homeowners who bought between 2018 and 2022 are seeing interest rate resets or simply stretched budgets. A permitted JADU generating $1,400-$1,900 monthly in the Pomona rental market changes your household math within months of completion, not years.
- An aging parent needs proximity, not a facility. The cost of assisted living in Los Angeles County exceeds $5,000 monthly. A room-to-ADU conversion with zero-step entry and grab-bar blocking keeps family close at a fraction of that, with the equity staying in your property.
- You have underused space that costs money to maintain. A basement that floods lightly every winter, a garage packed with storage, a den that hasn’t hosted guests in years. These spaces incur property tax, heating, and repair liability without generating return. Conversion turns liability into asset.
- Your employer has mandated return-to-office and your remote-work setup is obsolete. The home office you built in 2021 now sits empty. An Interior JADU repurposes that square footage for rental income while preserving a smaller workspace if needed. We design for flexibility: the same electrical rough-in supports office or residential use.
- You’re holding a written estimate that feels vague or incomplete. Estimates without line-item scope, without permit fees identified, without a completion guarantee. Under Haven Standard Clause 1, our written price includes every line item from drawings through final inspection. Bring us your existing estimate for a Free Second Opinion.
Our Junior ADU & Interior Conversion Process - Step by Step
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Site measure and feasibility study. We visit your Pomona property with laser measure, moisture meter, and camera. We record existing conditions, identify structural constraints, and verify setback, height, and lot coverage against Pomona’s zoning code. You receive a documented photo record of what we found, not what we felt, within 48 hours.
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Written price and scope. Within one week of measurement, we deliver a line-item written quote: design and permitting, construction, utilities, finishes, and a contingency line for unforeseen conditions. Under Haven Standard Clause 1, this price is locked at signing. No door-side upsells, no scope creep. We also note what the price explicitly excludes, so there’s no ambiguity.
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Permit set production. Our in-house designers produce architectural, structural, MEP, and Title 24 energy calculations as a single coordinated package. Los Angeles County’s ADU review track requires complete submittal; missing sheets trigger rejection and delay. We submit only after internal cross-check against Pomona’s most recent zoning interpretations.
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Construction and inspection. Our background-checked, uniformed crews execute the build according to the permitted drawings. A project manager visits weekly with camera, uploading progress to your client portal. We pull all permits and schedule all inspections, including the fire separation inspection that trips many Pomona conversions.
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Final walk and 365-Day Done Right Promise. At completion, we walk every room with you against the permit set and photo record. If the finished ADU is not built to the permitted drawings, we make it right, in writing, before you sign final acceptance. The promise is backed by Haven Standard Clause 5, not a handshake.
How Much Does Junior ADU & Interior Conversion Cost in Pomona?
A typical Interior JADU or room-to-ADU conversion in Pomona runs $85,000-$125,000 all-in, drawings through final inspection. Basement ADUs trend higher at $110,000-$155,000 due to moisture mitigation, egress window cutting, and slab work. Above-garage units range $130,000-$175,000 depending on whether the existing foundation requires reinforcement. Attached additions fall between $120,000-$165,000 based on square footage and finish level.
| Conversion Type | Typical Range in Pomona | Primary Cost Drivers |
|---|---|---|
| Interior JADU / Room-to-ADU | $85,000 - $125,000 | Kitchenette scope, separate meter, egress door |
| Basement ADU | $110,000 - $155,000 | Ceiling height, moisture, egress window, ventilation |
| Above-Garage ADU | $130,000 - $175,000 | Foundation capacity, structural framing, stairs |
| Attached Addition ADU | $120,000 - $165,000 | Square footage, utility extension, roof tie-in |
What moves your number within these ranges: existing conditions we discover during measurement, your finish selections, and whether your lot requires a setback variance or other entitlement. We price for the actual project, not a hypothetical average. Under Haven Standard Clause 1, the written price you receive before work starts is the price you pay, contingent only on change orders you initiate.
To avoid overpaying, compare line-item scope, not headline numbers. An estimate that omits permit fees, utility connection, or final cleaning will grow. Ours doesn’t. Call (657) 286-7915 for an exact quote on your specific property. Estimates are free, and we offer a Free Second Opinion on any written estimate already in hand.
Junior ADU & Interior Conversion Near Pomona - Our Service Area
We design, permit, and build Junior ADUs and interior conversions throughout the Pomona Valley and western San Gabriel Valley, including Montclair, San Dimas, Diamond Bar, Upland, Covina, Glendora, Chino, Chino Hills, West Covina, Ontario, and Rowland Heights. Most Pomona properties receive initial site measurement within one week of call scheduling. Properties in hillside zones north of Foothill Boulevard or within the Ganesha Hills Specific Plan may require additional geological review, which we identify during feasibility and price into the written scope.
Our permit set experience spans Los Angeles County’s unincorporated areas and the individual city departments in each of these jurisdictions, so we file correctly the first time rather than learning your city’s process at your expense.
Serving Pomona, CA - Our Local Coverage Area
We’re based in the Pomona 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 Pomona
A Junior ADU is a specific type of small, permitted dwelling unit created within the walls of an existing single-family home, up to 500 square feet, with an efficiency kitchen and separate exterior access. An interior conversion is the broader category that also includes converting basements, above-garage space, or rooms into fully independent ADUs, such as our Diamond Bar Junior ADU & Interior Conversion projects. At Ellery ADU Studio, we handle both under one contract, producing the permit set and managing construction so no gap exists between design intent and built result.
Most Interior JADUs in Pomona complete in 8-12 months, with 3-4 months for permit set and city review, 4-6 months for construction, and 2-4 weeks for final inspection and certificate of occupancy. Basement and above-garage conversions often extend to 10-14 months due to additional structural and MEP complexity. Under Haven Standard Clause 3, we provide a written schedule at contract signing and update it monthly. Call (657) 286-7915 for a timeline estimate based on your specific conversion type.
Interior JADUs and room conversions in Pomona typically run $85,000-$125,000 all-in; basement, above-garage, and attached addition projects range $110,000-$175,000 depending on structural requirements and finish level. Every project receives a line-item written price before work starts, per Haven Standard Clause 1, with no obligation to proceed. Call (657) 286-7915 for an exact quote on your property.
Yes. We specify and coordinate Boxabl, Plant Prefab, and other modular systems within the same single contract that covers your permit set and construction. Our permit set includes module connection details, crane access plans, and utility rough-in specifications that generic contractors often omit. Whether you have a specific brand in mind or want us to recommend based on your site constraints, we integrate the system into a cohesive build. Call (657) 286-7915 to discuss prefab options for your conversion.
ADU conversions are planned construction, not emergency work, so we do not promise same-day or overnight response. We do prioritize clients facing hard deadlines, such as loan rate locks or lease expirations, with accelerated permit set production and inspection scheduling where city capacity allows. Our live person answers calls 24/7 to discuss timeline pressure and determine what acceleration is realistically achievable. Call (657) 286-7915 to discuss your deadline.
Our 365-Day Done Right Promise covers every conversion: if the finished ADU is not built to the permitted drawings, we make it right, in writing, before you sign final acceptance. Beyond that, standard manufacturer warranties apply to fixtures, appliances, and materials we specify. We document every product warranty in your closeout package so you have single-point accountability, not a folder of manufacturer phone numbers. This promise is Haven Standard Clause 5, not a verbal assurance.
Gather any existing property surveys, recent appraisals, or previous architectural drawings you have. Note any known issues with the space you want to convert: moisture, foundation cracks, electrical panel capacity. We’ll measure everything ourselves, but prior documentation speeds feasibility analysis. If you have a written estimate from another firm, bring it for our Free Second Opinion. Call (657) 286-7915 to schedule; a live person answers 24/7.
Schedule Your Junior ADU & Interior Conversion Service in Pomona Today
Call (657) 286-7915 to schedule your free estimate. You’ll receive a site measurement, documented photo record, and line-item written price before any work begins, guaranteed under Haven Standard Clause 1. A live person answers our line 24/7. If you already have a written estimate in hand, ask for our Free Second Opinion. Nadia Ellery and the team at Ellery ADU Studio have served Pomona since 2015 with one contract, one written price, and one point of accountability from permit set through final inspection.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Pomona since 2015.