Fast, Reliable New Detached ADU Across San Dimas
A new detached ADU in San Dimas typically runs $210,000 to $385,000 all-in for a 500 to 800 square foot unit, drawings through final inspection. That range reflects the city’s two distinct permit paths: standard flat-lot parcels along Bonita Avenue and the equestrian-zoned foothill properties where fire-hardening and slope engineering add real cost. If you’re on a horse-zoned lot north of Arrow Highway or east of San Dimas Canyon Road, your project will follow the stricter wildland-urban interface rules. Call (971) 497-2402 and we’ll tell you exactly which path applies to your parcel before you spend a dollar.
Why Ellery ADU Studio Is San Dimas’s Preferred New Detached ADU Company
We’ve designed and permitted detached ADUs across San Dimas since 2015, and the projects here split into two clear camps. The first is the classic 1960s ranch off streets like Calle Alegre or Via Verde, where a standard detached unit goes through plan check cleanly. The second is the foothill parcel north of Foothill Boulevard, where the city’s building department expects a Very High Fire Hazard Severity Zone submittal and the reviewer will ask about your roof assembly before they ask about your floor plan.
Nadia Ellery runs our design-build studio, and she reviews every San Dimas permit set before it leaves our office. That matters here because the city’s plan check staff will not accept a generic Southern California ADU drawing set on a VHFHSZ parcel. They want to see Class A roofing specified, ember-resistant vent callouts, and fire-rated exterior assemblies on the elevations. We submit it right the first time, and the photo record we document on every visit proves what got built matches what got approved.
Our written price comes before any work starts, per Haven Standard Clause 1. You’ll see the full scope, the permit line items, and the fire-hardening line items on paper before you sign. No door-side additions later. If the finished unit isn’t built to the permitted drawings, our 365-Day Done Right Promise says we make it right, in writing, before the project starts.
Our New Detached ADU Services in San Dimas
Custom Built ADU
Custom detached ADUs in San Dimas run $240,000 to $385,000 depending on square footage and site conditions. On flat parcels near Lone Hill Avenue or the neighborhoods around San Dimas High School, a custom 1-bed or 2-bed unit follows a predictable path: engineered foundation, standard framing, stucco or Hardie siding, and a clean final inspection. On foothill lots off San Dimas Canyon Road, the custom route adds retaining walls, engineered foundations for slope, and fire-rated exterior assemblies that flat-valley cities like Covina never see.
Prefab ADU Installation
Prefab and modular units from Cover, Dvele, and Boxabl are a strong fit for San Dimas because the factory-built envelope arrives with consistent fire-rated assemblies. A prefab detached ADU here typically runs $190,000 to $310,000 installed, including the foundation, utility trenching, and city inspections. We coordinate the factory order, the crane, and the permit set under one contract, which means the fire-class documentation you need for your VHFHSZ parcel comes from the manufacturer and lands in your permit file, not lost between a dealer and a separate GC.
Modular ADU
Modular detached ADUs in San Dimas run $200,000 to $320,000 for a 1-bed or 2-bed unit with full kitchen and bath. The advantage on San Dimas’s larger equestrian lots is that the modular sections drop onto a prepared foundation in days, leaving more of your budget for the fire-hardening line items the city requires. We’ve specified Mighty Buildings and Cover panels on parcels where the owner wanted the speed of modular without sacrificing the documented compliance trail.
Studio ADU
A studio detached ADU in San Dimas runs $165,000 to $260,000 all-in. This is the most common choice for owners near the historic downtown along Bonita Avenue, where detached garages sit close to the house and the lot doesn’t allow a larger footprint. On foothill parcels, a studio still triggers the same Class A roof and ember-resistant vent requirements, so we always include those line items in the written price rather than discovering them at roof inspection.
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.
Common New Detached ADU Problems We See in San Dimas Homes
- Foothill lots with undocumented fill or slope conditions. We see this on parcels above Foothill Boulevard regularly. A standard slab spec fails the city’s drainage review, and the owner pays for rework. We pull the soils report before we quote.
- Old stables and tack rooms with no permit history. San Dimas has more accessory structures than most of the San Gabriel Valley. If the city building department can’t verify the structure’s legal status, the change-of-use to an ADU stalls. We pull that history before you buy materials.
- Roof assemblies below Class A on VHFHSZ parcels. A cheap bid will carry a standard composition roof on paper, then get rejected at plan check or hit a stop-work at roof inspection. Our San Dimas quotes include Class A from the start.
- Santa Ana wind exposure on north-facing eaves. Foothill properties get genuine wind-load challenges the flat neighborhoods don’t. We spec wind-rated hold-downs and shear details that a generic framing package won’t include.
Trusted Brands We Service in San Dimas
We specify and coordinate prefab systems from Cover, Dvele, and Boxabl for San Dimas projects. On VHFHSZ parcels, Cover’s panelized system carries documented fire-rated assemblies that satisfy the city’s plan check without custom engineering. Dvele’s envelope arrives with Class A roofing and ember-resistant detailing already specified. We keep the permit documentation for any brand we install in your project file, so the compliance trail is complete when your insurer asks for it. That documentation matters exactly as much as the structure itself.
Pricing for New Detached ADU in San Dimas, CA
Here are the honest ranges for San Dimas’s current market. A studio ADU on a flat parcel runs $165,000 to $260,000. A 1-bed detached ADU runs $200,000 to $310,000. A 2-bed on a foothill parcel with retaining work and full fire-hardening runs $280,000 to $385,000. What moves your number: whether your parcel is in the Very High Fire Hazard Severity Zone, whether you have slope, whether you’re converting an existing accessory structure, and what finish level you want. Every quote includes a written price before work starts, per Haven Standard Clause 1. No verbal estimate. No change orders later. Call (971) 497-2402 for your written quote.
We Also Serve Cities Near San Dimas
Our team works across the eastern San Gabriel Valley. From our Los Angeles office we serve San Dimas and dispatch crews locally to La Verne, Glendora, Covina, and Azusa. If you’re on a horse-zoned parcel in any of these foothill cities, the fire-hardening rules differ by jurisdiction, and we know which ones apply where. Visit our New Detached ADU service page for the full scope of what we build.
Serving San Dimas, CA - Our Local Coverage Area
We’re based in the San Dimas 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 San Dimas
Yes, if your parcel sits in the Very High Fire Hazard Severity Zone, which covers the northern and eastern foothill areas of San Dimas, including parcels off San Dimas Canyon Road and the streets above Foothill Boulevard. The city will require a Class A roof assembly, ember-resistant vents, and fire-rated exterior walls on the ADU. These requirements do not apply to similar ADUs a few miles south in Covina. To check your parcel’s zone, we can pull the city’s fire hazard map during a free estimate. Call (971) 497-2402 and we’ll confirm it in writing.
Yes, but only if the structure’s legal permit status can be documented with the city’s building department. San Dimas has a high number of equestrian-zoned parcels with existing stables, tack rooms, and hay barns that already carry active water meters and electrical panels. The city’s planning staff will require the original permit history before approving a change-of-use. We run that research first, because if the structure was never permitted, the conversion path closes and you’re looking at new construction instead. Call (971) 497-2402 for an exact answer on your structure.
Foothill parcels north of Foothill Boulevard need engineered wind-load hold-downs and shear details rated for the site’s exposure category, typically a step above what the flat neighborhoods require. Santa Ana winds channel through San Dimas Canyon and hit north-facing eaves with real force. Our permit sets specify the correct hold-downs and shear wall schedule from the start, so plan check passes without revision. A cheap quote that skips this line item gets returned at review and you eat the delay.
If your ADU is damaged and the insurer asks whether the structure met code, the answer comes from your permit file. If the Class A roof, ember-resistant vents, and wind-rated hold-downs are documented in the approved plans and the photo record from construction, the claim processes cleanly. If the work was done informally, the insurer may reduce or deny the payout. We provide a documented photo record on every visit and the final approved drawings at closeout, so the compliance trail is complete. That’s why we treat the permit set as the core deliverable.
Often yes. Foothill lots above Foothill Boulevard carry enough slope that a standard slab will fail the city’s drainage and slope review. The fix is an engineered foundation and, in many cases, a retaining wall before the ADU slab goes in. We include this cost in the written quote, not as a surprise after excavation. Call (971) 497-2402 for a site walk and a written price that covers the retaining work, the foundation, and everything else.
If you’re weighing a detached ADU in San Dimas, start with the parcel. We’ll tell you which fire zone you’re in, whether that old stable can become a unit, and what the whole project costs in writing. Call (971) 497-2402 to schedule a free estimate. Nadia Ellery will review your permit set personally.
Written by Nadia Ellery, Owner at Ellery ADU Studio, designing and permitting detached ADUs across San Dimas and the eastern San Gabriel Valley since 2015.