Trusted Garage Conversion ADU for Fontana Homeowners
Garage conversion ADUs in Fontana typically run $85,000-$165,000 all-in, from measured drawings through final inspection, with most projects permitted within 8-14 weeks and construction lasting 4-6 months. Since 2015, Ellery ADU Studio has designed, permitted, and built over 900 ADUs across the Inland Empire, every one at a written price agreed before any work started, per Haven Standard Clause 1. We serve Fontana homeowners in neighborhoods from Sierra Lakes to Southridge Village, from the older ranch tracts north of the 210 to the newer developments near Jurupa Hills. Call (909) 637-3715 to schedule your free estimate, or bring us any written estimate already in hand for a Free Second Opinion.
Fontana’s housing stock presents a specific opportunity. Thousands of homes built between 1960 and 1995 have attached two-car garages with adequate slab depth, existing electrical panels that can often be upgraded in place, and rooflines that simplify the conversion to conditioned living space. The city’s ADU ordinance, updated in 2020 and refined again in 2023, allows garage conversions by-right on most single-family lots, meaning no discretionary review if you meet objective standards. What derails most projects isn’t zoning, it’s the handoff between designer and builder. Ellery operates as a single-contract design-build studio, so the permit set, the construction documents, and the build itself are one scope, one price, one accountable party: us.
What Our Garage Conversion ADU Service Includes
Attached Garage Conversion
An attached garage conversion turns the structure already connected to your main house into a self-contained dwelling unit with its own kitchen, bathroom, sleeping area, and separate exterior entrance. In Fontana, these are the most common conversion type because the existing slab, roof, and at least one wall are already in place, reducing both structural complexity and cost. We see this most often in the North Fontana and Hunter’s Ridge areas, where 1980s and 1990s tract homes have 400-500 square foot two-car garages that convert cleanly to one-bedroom ADUs. Ellery measures your existing slab for thickness and reinforcement, determines whether your electrical panel can handle the additional load or needs a service upgrade, and produces a permit set that addresses the fire separation between units, a detail the city inspector will flag if it’s not drawn correctly.
Detached Garage Conversion
A detached garage conversion transforms a standalone structure into a separate dwelling unit, which means addressing utility runs across your yard and ensuring the building meets current energy code independently. Fontana’s older neighborhoods, particularly south of the 10 freeway and in the downtown-adjacent areas, have many detached garages on alley-accessed lots where this approach makes sense. The key challenge is typically the sewer lateral, if the garage was never plumbed, and the electrical service, which may need a new trench from the main meter. We handle the site plan, the utility coordination, and the PG&E or SCE service upgrade paperwork as part of our single contract, so you’re not hiring a separate civil engineer or waiting on utility approvals while your contractor stands idle.
Carport Conversion
A carport conversion starts with less structure, no walls and no garage door, but often gains flexibility because you’re not working around an existing enclosed box. In Fontana’s warmer pockets near the Jurupa Hills, where carports were common in 1970s construction, we regularly convert these to open-studio or bedroom-kitchenette ADUs by adding walls, insulation, and a proper roof assembly. The slab is the first question, carports often have thinner pours without footings, so we core-test to determine whether we can build on what’s there or need a perimeter foundation. Our permit set includes the structural calculations for this, not a guess that gets rejected at plan check.
Garage Partition & Bathroom Add
Some Fontana homeowners want to keep garage parking for one vehicle while converting the remaining space to an ADU, or add a bathroom and kitchenette to a portion of the structure without a full conversion. This requires careful space planning, the minimum ADU size in California is 150 square feet, but the practical minimum for a functional studio with bath is closer to 250. We draw the partition as a rated assembly, address ventilation for both zones, and ensure the remaining garage space still meets code for vehicle storage if that’s part of your plan. This is common in the Sierra Lakes area, where homes were built with oversized three-car garages that partition neatly.
Garage JADU
A Junior ADU, or JADU, is created within the walls of your existing home or attached garage, must be no more than 500 square feet, and requires owner-occupancy of either the main house or the JADU. In Fontana, garage JADUs work well for homeowners who want rental income or family housing without the full cost of a standalone ADU. The catch is the shared systems, your JADU can share a bathroom with the main house or have its own, but the kitchen must be “efficiency” style, and the entrance must be separate. We navigate these constraints in the permit set so you don’t discover them at inspection. Our drawings specify the door location, the kitchenette layout, and the owner-occupancy affidavit the city requires.
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 Garage Conversion ADU
Ellery ADU Studio specifies and coordinates prefab and modular systems from Cover, Dvele, Mighty Buildings, and Boxabl within the same single-contract design-build model we use for site-built work. With Cover, we’ve integrated their compact studio modules into garage conversion projects where the existing structure needs more than cosmetic work, using their panelized system to replace walls and roof while maintaining the original footprint. Dvele’s smart-home-ready units appeal to Fontana homeowners building for long-term rental income, and we coordinate their factory delivery with our site prep and utility tie-ins so the timeline doesn’t slip. Mighty Buildings’ 3D-printed polymer composite construction offers a faster weather-tight shell for detached garage replacements, and we’ve managed the crane-set and finish-out on several Inland Empire sites. Boxabl’s foldable Casita units, at 375 square feet, fit precisely into the footprint of a standard two-car garage and have become a popular option for homeowners who want a fully permitted, factory-built solution without the design ambiguity of a custom build.
Whether your project involves one of these systems or a conventional stick-frame conversion, our permit set addresses the structural, mechanical, and energy code compliance in full. We don’t hand you a manufacturer’s brochure and wish you luck with the city. The drawings are our product, and they carry the same written-price guarantee under Haven Standard Clause 1 regardless of construction method.
Before
AfterSigns You Need Garage Conversion ADU Right Now
- Your adult child needs housing but can’t afford Fontana’s market rents. A garage conversion ADU keeps family on the property without the friction of shared hallways and kitchens. The rental income, if you later choose to lease it, typically covers the project cost within 7-12 years at current Fontana rates.
- You’re carrying a mortgage rate from 2022-2024 and need additional income to stabilize payments. Many Fontana homeowners who bought at peak pricing are now exploring ADUs as a cash-flow strategy. A permitted, inspected garage conversion adds legal square footage that appraisers can count, unlike unpermitted work that creates disclosure problems at sale.
- The garage slab is cracking, the door is failing, and you’re facing $8,000-$15,000 in repairs anyway. In the Southridge Village and Oleander areas, we see 1970s slabs with significant spalling and rebar corrosion. Rather than pour money into a structure you’ll eventually replace, the same capital can convert it to income-producing space with a new foundation designed for residential load.
- Your property tax assessment is climbing and you want to maximize utility before a potential sale. California’s Proposition 19 allows homeowners over 55 to transfer their tax base, but buyers pay on the new value. A permitted ADU, documented in the permit history, is a feature that justifies asking price in Fontana’s competitive resale market.
- You’ve received a notice of violation for an unpermitted garage conversion already in progress. Fontana’s code enforcement division has stepped up inspections in response to state housing mandates, and red-tagging unpermitted units is increasingly common. We can assess what’s been done, determine what needs correction, and produce a permit set that brings the work into compliance, often without full demolition.
Our Garage Conversion ADU Process - Step by Step
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Site measure and feasibility review. We visit your Fontana property with a laser measure, moisture meter, and slab-core testing equipment if needed. Within 48 hours, you receive a written feasibility report: slab condition, electrical panel capacity, sewer lateral location, and any setback or height constraints specific to your zoning. This report includes a preliminary square footage and a rough budget range, so you know whether to proceed before spending on full drawings.
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Design and permit set production. Our architects produce construction documents that include floor plans, elevations, structural calculations, Title 24 energy compliance, and all Fontana-specific forms. The permit set is the core product, not an afterthought, and it undergoes internal peer review before submission. You receive a digital copy and one printed set for your records.
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Plan check and correction cycle. We submit to Fontana’s Building & Safety division and manage the correction cycle directly. Typical first review takes 4-6 weeks; our resubmittal addressing city comments usually clears in 2-3 weeks. We don’t charge extra for correction cycles, they’re built into our scope under Haven Standard Clause 5 (No Surprises).
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Construction at the written price. Once permitted, our crews begin with documented photos of existing conditions, then proceed through foundation repair or reinforcement, framing, MEP rough-in, insulation, drywall, finish carpentry, and final fixtures. Every visit generates a photo record you receive, showing what was found and what was done, not a summary of how it felt.
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Inspection, certificate of occupancy, and 365-Day Done Right Promise. We schedule all inspections, from rough to final, and don’t consider the project complete until the certificate of occupancy issues. After that, our written 365-Day Done Right Promise remains in effect: if the finished ADU is not built to the permitted drawings, we make it right, documented in your contract before work ever started.
How Much Does Garage Conversion ADU Cost in Fontana?
A typical attached garage conversion in Fontana runs $85,000-$125,000 all-in, from initial drawings through final inspection, as detailed in our Garage Conversion ADU cost guide. Detached garage conversions, with their additional utility trenching and often more extensive structural work, typically range $110,000-$165,000. Carport conversions start around $95,000 because you’re building walls and roof from scratch, though you may save on demolition. Garage partition projects, where you’re keeping some parking, run $45,000-$75,000 for the partial conversion. JADUs, with their smaller footprint and shared systems allowance, typically fall between $65,000-$95,000.
Several factors push these ranges up or down. Foundation condition is the biggest variable, a slab that needs replacement adds $15,000-$30,000. Electrical service upgrades, common in pre-1990 Fontana homes with 100-amp panels, add $3,500-$8,000. Sewer lateral extensions to a detached structure can run $8,000-$18,000 depending on distance and trenching complexity. Roof replacement, if the existing structure won’t carry the insulation and finish loads, adds $12,000-$22,000. What doesn’t change is the price you receive before work starts. Under Haven Standard Clause 1, the written price is locked at signing. No door-side upsells, no scope creep, no “we found something unexpected” at 80% completion.
Every free estimate we provide includes a line-item breakdown: design and permitting, demolition, foundation, framing, MEP, insulation and drywall, finishes, and project management. You see where the money goes before you commit. Call (909) 637-3715 for your written estimate, or bring us any competitor’s written quote for a Free Second Opinion.
Garage Conversion ADU Near Fontana - Our Service Area
Ellery ADU Studio serves Fontana directly and the surrounding communities where ADU demand is strongest: Garage Conversion ADU in Rialto to the west, Garage Conversion ADU in Bloomington to the south, plus Rancho Cucamonga, Glen Avon, Sunnyslope, Rubidoux, Pedley, Mira Loma, Ontario, Upland, and Eastvale. Most Fontana properties receive their initial site measure within 3-5 business days of calling. If you’re in the northern neighborhoods near the 210 or the southern tracts toward Jurupa Valley, we’re regularly in your area and can often coordinate visits with nearby projects to reduce scheduling friction.
Serving Fontana, CA - Our Local Coverage Area
We’re based in the Fontana 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 - Garage Conversion ADU in Fontana
A garage conversion ADU transforms an existing garage into a legally permitted, self-contained dwelling unit with kitchen, bathroom, sleeping area, and separate entrance. In Fontana, this is the most cost-effective way to add rental income or family housing because you’re working with existing structure rather than building new. Ellery handles the full conversion as a single contract, from measured drawings through certificate of occupancy.
Most Fontana garage conversion ADUs take 8-14 weeks for permitting and 4-6 months for construction, for a total project timeline of 6-9 months. Detached conversions with utility extensions or projects requiring foundation replacement may extend toward the longer end. We provide a written schedule with your price, and updates if city plan check or inspection timing shifts. Call (909) 637-3715 for a timeline specific to your property.
Attached garage conversions in Fontana typically run $85,000-$125,000 all-in; detached conversions range $110,000-$165,000; JADUs fall between $65,000-$95,000. Your specific price depends on foundation condition, electrical service capacity, and whether the existing roof structure can carry the new loads. Every Ellery estimate is a written, line-item quote before any work starts, per Haven Standard Clause 1. Call (909) 637-3715 for your exact number.
Yes. Ellery specifies and coordinates Cover, Dvele, Mighty Buildings, Boxabl, and other prefab systems within our single-contract model. We don’t sell you a module and disappear, we produce the site-specific permit set, manage utility tie-ins, and handle finish integration so the factory build and site work connect properly. The written price covers the complete scope, not just the box.
Yes. We regularly assess unpermitted work in Fontana, document what’s been done versus code requirements, and produce a permit set that brings the project into compliance. In some cases we can preserve significant portions of the existing work; in others, correction is more extensive. The feasibility review, with our findings and recommended path, is part of our standard site visit. Call (909) 637-3715 to schedule.
Every Ellery garage conversion ADU carries our 365-Day Done Right Promise: if the finished unit is not built to the permitted drawings, we make it right, in writing, before the project starts. This is backed by Haven Standard documentation, not a verbal assurance. We also pass through all manufacturer warranties on fixtures, appliances, and any prefab systems installed.
Gather any existing property surveys, your latest tax bill (which confirms APN and zoning), and if available, your original building plans. Note any known issues with the garage slab, roof, or electrical panel. We’ll measure everything ourselves, but your advance information speeds the feasibility assessment. The estimate itself is free, written, and delivered within 3-5 business days of our site visit. Call (909) 637-3715 to schedule.
Schedule Your Garage Conversion ADU Service in Fontana Today
Call (909) 637-3715 to schedule your free estimate. A live person answers 24/7, no voicemail queue. You’ll receive a written, line-item price before any work starts, a documented photo record on every visit, and the 365-Day Done Right Promise in writing. Bring us any competitor’s written estimate for a Free Second Opinion. Ellery ADU Studio has operated as a design-build studio since 2015, and we’ve delivered over 900 ADUs across the Inland Empire, every one at a price agreed in advance and documented at completion.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Fontana since 2015.