Fast, Reliable New Detached ADU Across Claremont
A new detached ADU in Claremont typically runs $285,000-$475,000 all-in, from permit set through final inspection, with construction lasting 8-14 months depending on site conditions and whether your lot falls within the High Fire Hazard Severity Zone. We’re the New Detached ADU team at Ellery ADU Studio, and we handle the full design-build chain - drawings, permit set, and construction - under one written contract at one written price. Our Los Angeles office coordinates scheduling and dispatch for Claremont projects, and crews are on local streets weekly from the Village to the northern foothills. Call (657) 239-4865 to schedule your free estimate.
Why Ellery ADU Studio Diamond Bar Is Claremont’s Preferred New Detached ADU Company
We’ve designed, permitted, and built ADUs across Claremont since 2015 - the same year California’s ADU laws opened the floodgates - and we know the difference between a flatland permit on Foothill Boulevard and a foothill plan check that triggers Chapter 7A fire compliance. Our license number appears on every page, our crews are background-checked and uniformed, and every Claremont project receives a documented photo record on every visit, not a summary of how it felt.
Claremont homeowners come to us after other bids have blown up mid-project. The 365-Day Done Right Promise, backed in writing before we start, means if the finished ADU doesn’t match the permitted drawings, we make it right. Under Haven Standard Clause 1, the price you sign is the price you pay - no door-side upsells, no scope creep. We also offer a Free Second Opinion on any written estimate already in your hand.
A live person answers our line 24/7. No voicemail queue, no callback that doesn’t materialize.
Our New Detached ADU Services in Claremont
Custom Built ADU
Custom built ADUs are our core work in Claremont, especially on the larger foothill lots north of Baseline Road where a site-specific design can capture mountain views and maximize rental income from the college market. We produce the full permit set in-house, coordinate with Claremont’s planning and building counter directly, and build from that same set - no designer-versus-builder blame gap when something doesn’t line up. A typical custom detached ADU in Claremont runs $320,000-$475,000 all-in, depending on square footage, fire-zone requirements, and utility tie-in complexity.
Prefab ADU Installation
Prefab ADU installation in Claremont makes sense when speed and predictability outweigh bespoke design. We specify and coordinate prefab systems from Mighty Buildings, Plant Prefab, and Tuff Shed within the same single contract that covers site prep, foundation, utility connections, and finish work. On flatland lots without fire-zone triggers, a prefab studio ADU in Claremont typically runs $285,000-$380,000 installed. On foothill parcels, we engineer the prefab shell for Chapter 7A compliance before it ever reaches your lot - no mid-project surprises at plan check.
Modular ADU
Modular ADUs differ from prefab in their construction standard - built to IRC or UBC rather than HUD code - and we coordinate modular systems from Dvele, Boxabl, and Plant Prefab for Claremont clients who need a full-permanent structure with financing advantages. Modular units arrive 80-90% complete, which compresses on-site construction time, but the foundation, utility trenching, and Claremont’s specific fire-zone engineering still require local expertise. We handle all of it under one written price.
Studio ADU & 1-Bed & 2-Bed ADU
Studio ADUs dominate the rental market near the Claremont Colleges - graduate students and visiting scholars want efficient, private space within walking distance of campus. We design studios starting at 350 sq ft with full kitchens and separate meters so the owner can capture top rent without sharing utilities. For north Claremont’s larger lots, 1-bed and 2-bed ADUs command even stronger rents from faculty and post-docs who stay longer and pay more. A 1-bed detached ADU in Claremont typically runs $340,000-$420,000; a 2-bed, $380,000-$475,000. Every quote includes the written price guarantee under Haven Standard Clause 1.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
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.
Trusted Brands We Service in Claremont
We specify and coordinate prefab and modular systems from Mighty Buildings, Boxabl, Plant Prefab, and Tuff Shed, plus we clad custom builds with James Hardie siding systems that satisfy Chapter 7A ignition-resistant requirements on Claremont’s foothill parcels. Our relationships with these manufacturers mean we can source lead times and warranty terms upfront, fold them into the written contract, and avoid the “call the factory yourself” handoff that derails other projects. For Claremont homeowners, this translates to one point of contact, one schedule, and one written price from foundation to final inspection.
Common New Detached ADU Problems We See in Claremont Homes
- Mid-century electrical and plumbing on flatland ranches. Homes built 1950s-1970s near Foothill Boulevard and south of the Village often carry original Zinsco or Federal Pacific panels and galvanized water supply lines. The ADU permit forces a main-house service upgrade and supply-line replacement that a walk-through bid never catches. We inspect the panel and plumbing before we quote, write line-item allowances into the contract, and price any surprises in writing before we cut lumber.
- Chapter 7A fire compliance on northern foothill lots. Parcels near Thompson Creek and the wilderness interface sit in California’s High Fire Hazard Severity Zone. Standard plan sets get kicked at plan check for missing ember-resistant soffit venting, Class A roofing assemblies, or ignition-resistant exterior cladding. We engineer for HFHSZ from the first permit drawing - no re-engineering, no timeline shock.
- Dry-rot and failed waterproofing in pre-war homes near the Village. Craftsman and Spanish Colonial Revival bungalows from the 1920s-1940s hide failed waterproofing and undersized joists behind intact stucco. Opening walls for the ADU’s utility tie-in turns up framing damage that an exterior bid can’t predict. Our field team documents everything with photos, presents line-item repairs in writing, and waits for approval.
- HVAC undersizing in a 105°F summer climate. Claremont’s San Gabriel Mountain foothill location produces sustained triple-digit heat. An ADU built with standard flatland insulation and a 1-ton undersized mini-split becomes unrentable by July. We size envelope and mechanical systems for actual local conditions, not code minimum.
Pricing for New Detached ADU in Claremont, CA
| ADU Type | Typical All-In Range (Claremont) | Key Cost Drivers |
|---|---|---|
| Studio ADU (prefab, flatland) | $285,000-$340,000 | Utility distance, foundation type, panel upgrade |
| Studio ADU (custom, flatland) | $320,000-$380,000 | Finish level, roof complexity, meter separation |
| 1-Bed ADU (custom or modular) | $340,000-$420,000 | Square footage, kitchen spec, fire-zone engineering |
| 2-Bed ADU (custom, foothill) | $380,000-$475,000 | Chapter 7A cladding, Class A roof, larger foundation |
These ranges reflect what we’ve written on actual Claremont contracts since 2015. What moves the number: your lot’s fire-zone status, the condition of existing electrical and plumbing, foundation requirements (slab-on-grade vs. raised on a sloped foothill parcel), and whether the city requires off-street parking mitigation. Under Haven Standard Clause 1, the price we write before work starts is the price you pay - no change orders without written approval. Call (657) 239-4865 for your free estimate.
We Also Serve Cities Near Claremont
Our crews work throughout the eastern San Gabriel Valley, including Claremont neighbors Montclair, Upland, Ontario, and Pomona. Each city carries its own planning quirks - Montclair’s utility coordination, Upland’s historic district overlays, Ontario’s fire-district boundaries - and we adjust the permit set accordingly rather than submitting the same plan five times.
Serving Claremont, CA - Our Local Coverage Area
We’re based in the Claremont area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - New Detached ADU in Claremont
Yes. North Claremont parcels in the High Fire Hazard Severity Zone must comply with California Building Code Chapter 7A, requiring ember-resistant soffit venting, Class A roofing assemblies, and ignition-resistant exterior cladding - none of which trigger on flatland lots south of Baseline Road or across the border in Montclair. We engineer for Chapter 7A from the first permit drawing so the plan check clears without re-submittal. Call (657) 239-4865 for an exact quote - estimates are free.
Because a walk-through bid can’t see inside walls. On a mid-century ranch near the Village with a detached garage on a ~8,000 sq ft lot, our crew tore out for a new detached ADU and found a 1960s Zinsco panel feeding undersized knob-and-tube branch wiring, galvanized supply lines, and a rear stem wall with dry-rot framing below grade. We wrote the panel upgrade, supply-line replacement, and framing repair as line-item allowances in the contract, ran them past the owner in writing as soon as the walls opened, and only cut lumber once approvals came back - then wrapped the shell in James Hardie cladding with ember-resistant soffit venting to satisfy the local fire requirements. The price only moves if you approve it in writing first. Call (657) 239-4865 for an exact quote - estimates are free.
The seven Claremont Colleges generate near-zero-vacancy demand that Pomona and Upland can’t match, so ADUs here rent faster and at higher rates - but the tenant profile shapes the design. Graduate students and visiting scholars want studios and 1-bed units with private entrances, full kitchens, and separate utility meters. Faculty and post-docs pay premium rents for 2-bed units with dedicated parking. We size and lay out the ADU for the actual rental market on your specific block, not a generic template. Call (657) 239-4865 for an exact quote - estimates are free.
Three paths: convert the garage to a Junior ADU (cheaper, faster, size-capped), demolish and replace with a new detached ADU (full rental income, no size cap), or keep the garage and build a new detached ADU elsewhere on the lot (best for rental yield, requires adequate setbacks). On the 7,000-10,000 sq ft lots common near the Village, we often see enough depth for a new detached ADU behind the garage while preserving off-street parking. We survey the lot, check setbacks against Claremont’s zoning, and present the buildable options with written prices for each. Call (657) 239-4865 for an exact quote - estimates are free.
We do all three - custom, prefab, and modular - under the same single contract. Prefab from Mighty Buildings or Plant Prefab works well on flatland lots without fire-zone triggers. Modular from Dvele or Boxabl suits clients who need IRC-compliant structures for conventional financing. Custom builds dominate foothill parcels where Chapter 7A engineering and site-specific design are non-negotiable. We specify the right system for your lot, your timeline, and your budget, with one written price before work starts. Call (657) 239-4865 for an exact quote - estimates are free.
Ready to see what a new detached ADU looks like on your Claremont lot? Call (657) 239-4865 to schedule your free estimate. Nadia Ellery and our team will walk the property, photograph existing conditions, and return a written line-item quote with no obligation to proceed.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Claremont since 2015.