Fast, Reliable New Detached ADU Across Brentwood
A new detached ADU in Brentwood typically runs $285,000-$485,000 all-in, from the first site measurement through final inspection, and the city’s architectural-review process adds roughly 4-6 weeks to the front of the schedule. We handle that submittal ourselves, staged so construction never starts before the committee signs off. Ellery ADU Studio Westchester has designed, permitted, and built ADUs across Brentwood’s planned subdivisions since 2015 - we know the palette, the height expectations, and the HOA grey zones that stall projects when they’re treated as afterthoughts. Call (213) 698-7591 to schedule your free estimate.
Our crews serve Brentwood from the San Francisco Bay Area office, with scheduling and permit coordination handled locally. We know the difference between a tract off Balfour Road and a master plan near the Delta, and we file accordingly.
Why Ellery ADU Studio Westchester Is Brentwood’s Preferred New Detached ADU Company
We’ve completed detached ADUs on the wide lots off Lone Tree Way, in the streets behind Veterans Park, and in the newer developments south of Marsh Creek Road. Brentwood’s 1990s-2000s building boom produced a housing stock almost unique in Contra Costa County: large-lot, 3-car-garage tract homes on 6,000-10,000+ sq ft lots with generous rear setbacks and side yards. That spatial profile means detached ADUs here are rarely killed by coverage math. The fight is almost always architectural review, and we’ve filed enough of those packets to know which roof pitches, siding samples, and color palettes sail through.
Our reviews from Brentwood clients consistently cite two things: the written price that didn’t change, and the photo record they received at every visit. Under Haven Standard Clause 1, every project is quoted with a written price before any work begins - no “call for a quote,” no range that widens once you’re committed. Our 365-Day Done Right Promise is backed in writing before the first shovel hits dirt.
Response time to Brentwood is typically next-day for site visits, with permit packets filed within 48 hours of contract signing. A live person answers calls 24/7 - no voicemail queue, no callback that doesn’t materialize.
We also offer a Free Second Opinion on any written estimate already in hand. If another design-build practice has quoted your Brentwood lot, send it over. We’ll tell you what’s solid, what’s missing, and whether the permit timeline they’ve promised matches what the city’s actually running.
Our New Detached ADU Services in Brentwood
Custom Built ADU
Custom built ADUs in Brentwood start around $320,000 and run to $485,000+ depending on square footage, foundation type, and finish level. The advantage on these lots is siting flexibility - we can orient for afternoon Delta breezes, set back from the main home’s sight lines, and design roof pitches that satisfy both the city’s architectural review and any lingering HOA CC&R clauses. Every custom project includes the full permit set, structural calculations, and the documented photo record on every visit.
Prefab ADU Installation
Prefab ADU installation in Brentwood typically ranges $285,000-$395,000 all-in, including site prep, foundation, utility tie-ins, and finish work. We specify and coordinate systems from Plant Prefab, Boxabl, and Tuff Shed within the same single contract that covers design and permitting - no finger-pointing between the box supplier and the local crew. On Brentwood’s flat, spacious lots, crane access and module delivery are usually straightforward, and we schedule the set day so the foundation cure and the architectural-review sign-off align.
Modular ADU
Modular ADUs in Brentwood fall in the $295,000-$420,000 range, with the factory build shaving 6-10 weeks off the overall calendar. The key local consideration is the architectural-review packet: modular suppliers often default to standard elevations that don’t match Brentwood’s palette, so we front-load the design phase to get committee approval before the factory cuts steel. We’ve coordinated Dvele and Mighty Buildings modules through this process - the factory build and the city review run parallel, not sequential.
Studio ADU
Studio ADUs in Brentwood run $285,000-$350,000 for detached units under 500 sq ft. These are popular with homeowners near the 94513 core who want rental income without the footprint of a 1-bed. Cooling is critical: Brentwood’s inland valley location produces summer highs routinely hitting 100-110°F, making mini-split sizing and insulation spec far more important than in coastal Contra Costa cities. We size the envelope for peak load, not average.
1-Bed & 2-Bed ADU
1-bed detached ADUs in Brentwood typically run $310,000-$395,000; 2-bed units run $365,000-$485,000. These are the workhorses of Brentwood’s ADU market - multigenerational families and long-term rental investors both want the separate bedroom count. On these larger units, the architectural-review scrutiny intensifies: height, roof pitch, and exterior material matching become the determining variables, and we submit the full elevation packet with James Hardie color-matched samples to head off revision cycles.
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.
Trusted Brands We Service in Brentwood
Ellery ADU Studio specifies and coordinates prefab and modular systems from Plant Prefab, Boxabl, and Tuff Shed, with James Hardie siding as our standard exterior finish for custom builds. We don’t drop-ship and disappear - every system is integrated into the same single contract that covers the permit set, site prep, and final inspection. For Brentwood clients, that means the panelized shell delivery is scheduled against the architectural-review calendar, not dropped onto a half-prepared site. Our crews have handled Boxabl set days on wide Brentwood lots where crane positioning is simple, and we’ve coordinated Plant Prefab installs where the factory finish had to be modified to match the city’s palette requirements. The parts are local, the knowledge is local, and the warranty is single-source.
Common New Detached ADU Problems We See in Brentwood Homes
- Architectural-review palette mismatches. Brentwood’s review committee expects roof pitches, siding textures, and color schemes that harmonize with the existing tract architecture. Submitting a flat-roof modern box on a traditional subdivision street gets bounced back for revisions that add 3-4 weeks.
- HOA CC&R grey zones in master-planned communities. Several Brentwood developments, including 55+ communities like Trilogy at the Vineyards, carry CC&Rs recorded before California’s full ADU preemption statutes took effect. The city permit is clean, but the HOA enforcement threat can still stall construction if the design-review packet doesn’t explicitly address exterior-finish clauses.
- Undersized cooling for inland valley heat. Brentwood’s summer peaks of 100-110°F punish ADUs spec’d for coastal Bay Area loads. We see mini-splits that can’t maintain setpoint on the first August afternoon, forcing costly envelope upgrades after occupancy.
- Garage-truss structural complications. Brentwood’s 3-car garages are often tied into the main home’s truss system in ways that complicate ceiling height compliance for conversion ADUs - a framing quirk that makes detached new construction the cleaner path on many lots, even when the garage looks spacious.
Pricing for New Detached ADU in Brentwood, CA
A new detached ADU in Brentwood typically costs $285,000-$485,000 all-in, with the final number driven by square footage, foundation type (slab-on-grade vs. raised), utility run length, and finish level. Prefab and modular systems cluster at the lower end of that range; fully custom builds with premium finishes push the upper bound. What doesn’t change is the written price: under Haven Standard Clause 1, every project is quoted with a fixed, line-item price before any work begins. No change orders, no scope creep, no surprise foundation upgrade once the slab is cut.
Factors that move the needle on Brentwood lots: distance to sewer connection (some developments have stubbed but unactivated laterals), electrical panel capacity in 1990s-era homes that may need a service upgrade, and the architectural-review cycle itself - a well-prepared packet moves in 4-6 weeks; a bounced submission adds that time again. We front-load the design phase specifically to avoid the second scenario.
Call (213) 698-7591 for an exact quote on your lot. Estimates are free, and we provide a Free Second Opinion on any written estimate already in hand.
We Also Serve Cities Near Brentwood
Our crews handle New Detached ADU in Brentwood and surrounding communities including Sherman Oaks, Studio City, West Hollywood, and Beverly Hills. Scheduling and permit coordination are managed from our San Francisco Bay Area office, with local crews dispatched to each jurisdiction. The architectural-review expertise we apply in Brentwood translates directly to the design-review processes in these neighboring cities.
Serving Brentwood, CA - Our Local Coverage Area
We’re based in the Brentwood 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 Brentwood
Yes, Brentwood’s architectural review typically requires roof pitch, siding texture, and color palette that harmonize with the existing home and subdivision character. We submit elevation drawings and physical material samples - often James Hardie color-matched siding - as part of the initial packet to avoid revision cycles. Call (213) 698-7591 and we’ll review your specific street’s built context.
Brentwood’s architectural review adds roughly 4-6 weeks to the front of the schedule when the initial packet is complete; a bounced submission for palette or height issues adds another 3-4 weeks. We stage construction so the foundation and rough-in begin the week after sign-off, meaning no exposed framing sits waiting through the committee cycle. Call (213) 698-7591 to discuss your target move-in date.
On most Brentwood lots, yes - the 6,000-10,000+ sq ft parcels and generous setbacks mean detached ADUs are rarely constrained by coverage limits, unlike older, denser East Bay cities. However, Brentwood’s garages are often structurally tied into the main home’s truss system, complicating conversion ceiling-height compliance. Detached new construction avoids that framing quirk entirely. Call (213) 698-7591 and we’ll assess your specific lot and garage.
Brentwood’s inland valley location produces summer highs of 100-110°F, among the hottest in the greater Bay Area, while Walnut Creek’s closer proximity to the coastal influence moderates peaks significantly. That temperature gap means mini-split sizing, insulation R-value, and window SHGC ratings must be spec’d for peak load, not average conditions. We size every Brentwood ADU envelope for those August afternoons. Call (213) 698-7591 for a load calculation on your design.
We do - Ellery ADU Studio prepares and files the complete submittal, including site plan, elevations, structural calculations, and material samples, as part of our single-contract design-build service. The homeowner does not interface with the city planning counter or the HOA architectural committee directly. Under Haven Standard Clause 5 (No Surprises), the scope is locked at signing; no door-side upsells, no scope creep. Call (213) 698-7591 to start your packet.
Our crew just finished a 1-bed detached ADU on a wide side yard off a Brentwood tract lot, where the homeowner’s main concern was the HOA letter that arrived after the city had already stamped the plans. We front-loaded the design-review packet - site plan, elevations, and James Hardie color-matched siding samples that met both the city’s architectural review palette and the CC&R’s exterior finish clause - and staged the panelized shell delivery so the foundation and rough-in were done the week before sign-off, meaning nothing sat exposed while we waited. The result: no half-finished framing sitting in a Brentwood backyard through the committee cycle.
Ready to build? Call (213) 698-7591 to schedule your free estimate. Every project starts with a written price, a documented photo record, and the 365-Day Done Right Promise - backed in writing, before any work begins.
Written by Nadia Ellery, Owner at Ellery ADU Studio Westchester, serving Brentwood since 2015.