New Detached ADU in San Dimas - Design, Permits and Build Under One Contract

Fast, Reliable New Detached ADU Across San Dimas

A new detached ADU in San Dimas typically runs $185,000-$340,000 all-in, from permit-ready drawings through final inspection, with most projects completing in 8-14 months depending on site conditions and whether the structure is custom-built or prefab. We’re the New Detached ADU team at Ellery ADU Studio Pomona, and we’ve been designing, permitting, and building detached ADUs across the Pomona Valley since 2015. Our crews serve San Dimas directly, with dispatch and scheduling coordinated from our Los Angeles office. Call (657) 286-7915 to schedule your free estimate.

Call (657) 286-7915

Why Ellery ADU Studio Pomona Is San Dimas’s Preferred New Detached ADU Company

San Dimas homeowners know their lots. Many sit on generous parcels by LA County standards, especially in the older neighborhoods off Bonita Avenue and the foothill streets north of Foothill Boulevard, where detached garages and outbuildings are common. We’ve designed and permitted ADUs on those lots. Our 900+ ADU portfolio since 2015 includes projects throughout the San Gabriel Valley, and San Dimas’s specific conditions - the horse-zoned parcels near Puddingstone Reservoir, the Very High Fire Hazard Severity Zones in the northern hills, the cemented Puddingstone conglomerate that complicates trenching - are conditions we’ve worked through, not around.

Every project starts with a written price before any work begins, per Haven Standard Clause 1. No “call for a quote” here. You get a line-item scope, a documented photo record on every visit, and our 365-Day Done Right Promise in writing. A live person answers calls 24/7 at (657) 286-7915. And if you already have a written estimate in hand, we offer a Free Second Opinion - we’ll review the scope, the permit strategy, and the line items against what we’ve seen on San Dimas sites.

Our New Detached ADU Services in San Dimas

Custom Built ADU

Custom built ADUs in San Dimas typically range from $220,000-$340,000 all-in, depending on square footage, foundation type, and whether we’re trenching through the Puddingstone conglomerate for utilities. On the alluvial flats south of the 210 Freeway, where soils are softer and lots are flatter, costs trend toward the lower end. In the foothills north of Via Verde, fire-hardening requirements and rock excavation push projects toward the higher range. We handle the full permit set, the structural calcs, and the construction under one contract - no designer-builder blame gap when something doesn’t match.

Prefab ADU Installation

Prefab ADU installation in San Dimas runs $185,000-$280,000, including site prep, foundation, utility connections, and finish work. We specify and coordinate systems from Abodu, Cover, and other prefab manufacturers, integrating their production schedules with San Dimas’s permit timeline. The city requires full plan review even for factory-built units, and we manage that submittal as part of our single contract. On tight lots near the historic downtown corridor, crane access and staging become critical path items we address in the initial site survey.

Modular ADU

Modular ADUs differ from prefab in their structural certification and transport method, and in San Dimas they typically run $195,000-$295,000 all-in. The modular units we coordinate are built to CBC compliance in factory conditions, then set on permanent foundations. For hillside parcels in the Very High Fire Hazard Severity Zone, we specify James Hardie siding and other fire-resistant exterior finishes that satisfy both the modular manufacturer’s warranty and CAL FIRE’s local requirements. One contract covers factory coordination, transport, set, and finish.

Studio ADU

Studio ADUs in San Dimas - typically 350-450 square feet - run $185,000-$250,000 for custom construction, or $165,000-$220,000 for prefab or modular alternatives. These compact units are well-suited to the secondary outbuildings common on San Dimas’s larger lots, including the stables and tack rooms in the northern horse-zoned areas. Converting an existing agricultural structure to a residential studio ADU requires full habitability upgrades: insulation, egress windows, residential electrical and plumbing, and often a new foundation. We price that scope completely upfront, not as a “remodel plus surprises.”

1-Bed & 2-Bed ADU

One-bedroom detached ADUs in San Dimas typically run $210,000-$290,000; two-bedroom units run $260,000-$340,000. The bedroom count drives septic or sewer capacity calculations, especially on older properties near Bonita Avenue where sewer laterals may date to the 1960s. We verify utility capacity during the feasibility phase, before the permit set is drafted. For 2-bedroom units on tight lots, we also analyze setback variances - the extra distance the city requires between your new ADU and the property line - to confirm the buildable envelope before you commit to the project.

Trusted Brands We Service in San Dimas

We specify and coordinate prefab and modular systems from Abodu, Cover, Tuff Shed, and James Hardie, integrating their products into our single-contract design-build workflow. James Hardie siding is our standard specification for any San Dimas project in the Very High Fire Hazard Severity Zone - it satisfies CAL FIRE’s fire-hardening requirements without the maintenance liability of wood-based alternatives. For prefab units, we maintain active coordination channels with Abodu and Cover, which means their production schedules are visible to us during the San Dimas permit review period, so factory and city timelines don’t conflict. Every brand we specify is backed by our written warranty and our 365-Day Done Right Promise.

Common New Detached ADU Problems We See in San Dimas Homes

• Stable-to-ADU conversions treated as cosmetic remodels. On horse-zoned lots near Puddingstone Reservoir, we regularly see owners assume a 1970s tack room or stable needs only paint and flooring. These structures were built to agricultural standards, not residential code. Missing insulation, egress windows, or residential electrical and plumbing bring plan-check rejections that a standard garage conversion wouldn’t face.
• Trenching estimates based on flatland assumptions. The cemented Puddingstone conglomerate formation in the San Dimas foothills can stall excavation for sewer and water laterals for days. A quote written for alluvial-flat soils below the 210 will not survive first contact with this geology. We price trenching by soil condition, not by zip code.
• Fire-hardening overlooked in foothill zone permits. San Dimas’s northern parcels fall within CAL FIRE’s Very High Fire Hazard Severity Zone. ADU permits in these areas require fire-resistant exterior materials, ember-resistant vents, and often specific setback clearances. Ignoring this in the design phase means redesigning at plan check.
• Neighbor relations mismanaged on tight lots. San Dimas’s density-sensitive work-hour and noise ordinances, combined with party-wall notice expectations on narrow parcels, can turn a permitted project into a stop-work order. We sequence noisy work within permitted hours, stage materials to maintain neighbor access, and document our site cleanliness with the same photo record we provide to clients.

Pricing for New Detached ADU in San Dimas, CA

We Also Serve Cities Near San Dimas

Our crews work throughout the eastern San Gabriel Valley and western Inland Empire, including San Dimas, Glendora, Covina, Pomona, and Diamond Bar. Each city has distinct zoning, soil conditions, and fire hazard mapping, and we adjust our permit strategy and pricing accordingly. The Puddingstone conglomerate issue, for instance, is largely absent in Covina’s flatter terrain, while Diamond Bar’s hillside zones present their own access and staging challenges.

FAQs - New Detached ADU in San Dimas