New Detached ADU in Fontana - One Fixed Price, Permits Handled

Fast, Reliable New Detached ADU Across Fontana

A new detached ADU in Fontana typically runs $185,000-$340,000 all-in, from permit-ready drawings through final inspection, depending on whether you choose a custom stick-built structure or a prefab system like Mighty Buildings or Boxabl. Most Fontana projects move from signed contract to permit submittal in 6-10 weeks, with construction lasting 4-8 months for custom builds or 2-4 months for prefab installations. Call (909) 637-3715 to schedule your free estimate - every project receives a written price before any work begins, per Haven Standard Clause 1.

Call (909) 637-3715

We’ve designed, permitted, and built ADUs across Fontana since 2015, from the compact 1950s worker tracts near the old Kaiser Steel corridor in 92335 to the sprawling master-planned subdivisions of North Fontana in 92336. Our crews coordinate dispatch from our Inland Empire office, and we know the difference between a South Fontana lot where every square foot of coverage counts and a North Fontana parcel with room for a 1,200 sq ft detached unit plus parking. That local knowledge shows up in your permit set, not just our conversation.

Why Ellery ADU Studio Fontana Is Fontana’s Preferred New Detached ADU Company

Fontana homeowners have left us reviews citing the documented photo records we deliver after every site visit - evidence of what we found, not a summary of how we felt about it. Our 900+ ADUs designed, permitted, and built since 2015 include dozens in Fontana proper, and our 365-Day Done Right Promise is backed in writing before your project starts: if the finished ADU doesn’t match the permitted drawings, we make it right.

Response time matters here. When you call (909) 637-3715, a live person answers 24/7. We can typically walk your Fontana lot within 48 hours of first contact, and we bring a preliminary coverage analysis based on your parcel’s zoning - no waiting for a callback that doesn’t materialize.

What separates us from contractors who “also do ADUs” is our single-contract design-build model. The drawings, the permit set, and the construction are one scope at one written price. When our New Detached ADU team finds a shared-panel wiring layout on a North Fontana garage conversion, we don’t point at an architect who isn’t on the job. We redesign the electrical and keep the project moving.

Our New Detached ADU Services in Fontana

Custom Built ADU

Custom stick-built detached ADUs are what most Fontana homeowners picture: framed on-site, tied to your existing utilities, designed to match your main home’s stucco-and-tile aesthetic. In North Fontana’s 1990s-2000s tracts, we regularly spec these at 600-1,000 sq ft with full kitchens and in-unit laundry. The trade-off is time - typically 6-8 months construction - and the advantage is flexibility on a lot with slope, setback, or utility complications that prefab can’t accommodate. We price these at $220,000-$340,000 all-in for Fontana, including the dedicated permit submittal to the city’s own building department.

Prefab ADU Installation

Prefab systems from brands like Plant Prefab or Boxabl arrive in modules and set in days, not weeks. For Fontana’s Santa Ana wind corridor, we specify hot-dip galvanized or stainless connection hardware - never the coastal-grade electroplated fasteners that rust through in two seasons here. A typical prefab studio or 1-bedroom in Fontana runs $185,000-$260,000 installed, with permit timelines shortened because the manufacturer provides engineered drawings the city has seen before. This is where we often steer South Fontana homeowners on tighter lots who need speed and predictability.

Modular ADU

Modular construction - built in-factory to California Building Code, then transported and craned onto your foundation - splits the difference between custom and prefab. Mighty Buildings’ 3D-printed fiber-reinforced polymer panels are one system we coordinate under our single contract. Fontana’s 105-112°F summer highs make factory-controlled construction attractive: no rain delays, and the thermal performance is tested before delivery. Modular detached ADUs in Fontana typically range $200,000-$290,000.

Studio ADU

The studio detached ADU - one open room, bath, kitchenette, 300-450 sq ft - is the most common starting point for Fontana’s multigenerational households seeking a casita for parents or adult children. We’ve built these across the city, from compact South Fontana lots where we max out at 400 sq ft under coverage rules to North Fontana parcels where a 450 sq ft studio with a small patio is straightforward. Studios run $185,000-$240,000 in Fontana, and the smaller footprint keeps Title 24 HVAC costs manageable even with our upsized cooling spec.

1-Bed & 2-Bed ADU

One-bedroom detached ADUs (500-700 sq ft) and two-bedroom units (700-900 sq ft) are where Fontana’s North Fontana lots shine. The 7,000-10,000+ sq ft parcels common in subdivisions near Summit Avenue and the 210 corridor accommodate these comfortably with parking and setbacks intact. A 1-bedroom detached ADU in Fontana typically runs $240,000-$290,000; a 2-bedroom, $290,000-$340,000. Both require the enhanced Title 24 insulation and HVAC sizing we spec for Fontana’s climate - under-sizing here means a unit that’s unusable in July and August.

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Trusted Brands We Service in Fontana

We specify and coordinate prefab and modular systems from Mighty Buildings, Boxabl, Plant Prefab, and Tuff Shed within the same single contract that covers your custom design-build work. For Fontana’s Santa Ana wind corridor, we order these systems with upgraded fastener packages - stainless or hot-dip galvanized roof clips, marine-grade door hardware, sealed paver joints - because we’ve seen coastal-grade electroplated screws rust through on railings and fence posts within two seasons here. The factory ships what we specify; we don’t accept substitutions at the site. That materials discipline is part of why our Fontana projects pass inspection clean and hold up over time.

Common New Detached ADU Problems We See in Fontana Homes

• Santa Ana wind abrasion destroys coastal-grade hardware. The grit-laden gusts that blow through Fontana’s corridors strip electroplated fasteners on roofing, railings, and fence posts within a few seasons. We specify hot-dip galvanized or stainless hardware on every detached ADU we build here, and we seal paver joints against wind-driven sand infiltration. The upfront cost difference is modest; the replacement cost is not.
• LA County ADU forms submitted to Fontana’s San Bernardino County building department. Fontana runs its own municipal building department, entirely separate from LA County’s streamlined pathways. Homeowners who downloaded LA-centric checklists arrive at the counter with wrong forms, wrong setback assumptions, and wrong utility-separation requirements. Our permit sets are submitted to Fontana’s specific requirements from day one.
• Title 24 cooling loads underestimated for 105-112°F summers. A 500 sq ft detached ADU in Fontana needs insulation and HVAC capacity sized for extremes that coastal projects never see. We regularly review competitor estimates that spec 1.5-ton systems where 2.5 tons are required; our permit sets include Manual J load calculations that hold up at Fontana’s plan check.
• North Fontana shared-panel garage wiring complicates electrical scope. The three-car attached garages common in North Fontana’s 1990s-2000s tracts often share the main home’s electrical panel in a configuration Fontana’s permit technicians flag on nearly every submittal. For detached ADU projects that tie into existing service, we pull a dedicated sub-panel before framing starts - a line item that’s often underestimated in initial budgets.

Pricing for New Detached ADU in Fontana, CA

We Also Serve Cities Near Fontana

Our crews work throughout the Inland Empire, including Fontana and neighboring Bloomington, Rialto, Mira Loma, and Rancho Cucamonga. Each city operates under its own building department with distinct submittal requirements - San Bernardino County’s unincorporated areas differ from Fontana’s municipal process, and Rancho Cucamonga’s is separate again. We maintain current permit sets and relationships with plan checkers across all five jurisdictions.

FAQs - New Detached ADU in Fontana