New Detached ADU in West Hills - Plans, Permits & Build, One Fixed Price

Fast, Reliable New Detached ADU Across West Hills

A new detached ADU in West Hills typically costs between $230,000 and $410,000 all-in, from permit set through final inspection. In the VHFHSZ blocks near the Santa Monica Mountains foothills, expect the fire-hardening requirements to add $12,000 to $28,000 compared to a flatland Canoga Park build. That’s the honest range. Call (971) 497-2402 and we’ll write you a fixed price before any work starts, per Haven Standard Clause 1.

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We’ve designed, permitted, and built detached ADUs across West Hills since 2015, the year California’s ADU landscape opened up. Our crews know which West Hills inspectors check which details, which hillside lots trigger geotechnical review, and which 1960s ranch homes still carry original 100-amp panels. That local knowledge is exactly what a detached ADU bid needs here because West Hills is not the rest of the Valley.

Why Ellery ADU Studio Is West Hills’s Preferred New Detached ADU Company

We run a design-build studio, not a contractor brokerage. The drawings, the permit set, and the construction sit under one contract at one written price. That matters in West Hills because the VHFHSZ overlay demands coordination between your architect’s fire-hardening details and your builder’s material order. When those are two different companies, someone points at the other. With us, there’s no one to point at.

Nadia Ellery leads every West Hills project. Since 2015, our studio has designed, permitted, and built 900+ ADUs across greater Los Angeles, each one with a written price before work began and a documented photo record when work ended. That record is not a courtesy. It’s evidence of what we found, what we did, and what passed inspection. West Hills homeowners who’ve had a previous contractor fail framing inspection over ember-resistant vents tell us that evidence is what made them call.

Our crews serve West Hills directly. Scheduling is coordinated from our Los Angeles office, but the people who show up know the Castle Pines tract, the hillside lots south of Roscoe, and the flatland pockets near Platt Avenue. They know the LADBS inspectors who serve this area and what those inspectors flag. A live person answers our phones 24/7 at (971) 497-2402, so when you call about your West Hills ADU, you reach a person, not a voicemail queue.

Our New Detached ADU Services in West Hills

Custom Built ADU

A custom detached ADU on a West Hills lot gives you full control over layout, roofline, and elevation. Most of our West Hills clients are working with 8,000 to 14,000-plus square foot lots, which gives a real rear-yard footprint for a 700 to 1,000 square foot unit. On post-war ranch lots, we typically site the ADU along the western or southern property edge, but every placement starts with a setback check against the VHFHSZ-adjacent hillside conditions that LADBS applies to canyon-side parcels.

Prefab ADU Installation

Prefab speeds up the build, but West Hills fire requirements still apply to the foundation and the site work under it. We specify and coordinate prefab systems from Cover, Dvele, and Mighty Buildings within our single contract, so the prefab factory and the local crew answer to one written scope. On a West Hills lot inside the VHFHSZ, we handle the ember-resistant venting, Class A roof integration, and fire-rated exterior detailing that the factory unit alone doesn’t cover.

Modular ADU

Modular construction works well on West Hills lots with clear crane access from the street. The westernmost Valley blocks are flatter and more accessible; the hillside-adjacent lots south of Victory often are not. We assess that at the first site visit and tell you plainly whether modular makes sense or whether a stick-built custom unit will actually cost less once crane logistics and fire-hardening adjustments are priced. The written quote reflects the West Hills site, not a generic modular catalog price.

Studio ADU

A studio ADU, typically 350 to 500 square feet, is the most cost-efficient detached unit for a West Hills rental or a quiet workspace. Most of our studio builds in this area run $180,000 to $290,000. On a 1960s West Hills ranch, the studio ADU often pairs with a panel upgrade and a small utility trench, and we write both into the same fixed price before we start digging.

Trusted Brands We Service in West Hills

We install, specify, and coordinate prefab and modular systems from Cover, Dvele, and Mighty Buildings for West Hills clients. When we quote a prefab or modular ADU, the brand’s unit price and the local West Hills site work appear as separate lines on the same written proposal, so you see exactly what the factory charges and exactly what the fire-hardening, foundation, and utility work costs here. We coordinate directly with the manufacturer, which means you don’t get stuck between a factory in another state and a local inspector with West Hills-specific requirements.

Common New Detached ADU Problems We See in West Hills Homes

• Fire-hardening inspection failures on standard Valley-spec framing. Out-of-area contractors frame with standard eave vents and standard roofing, then fail LADBS inspection in the VHFHSZ blocks because the vents aren’t 1/16-inch ember-resistant mesh and the roof isn’t a full Class A assembly. We spec West Hills fire requirements from the permit set onward, so the framing inspection passes the first time.
• Original 100-amp panels that can’t carry an ADU. The majority of 1950s-to-1970s West Hills ranch homes still carry a 100-amp service. LADBS requires a 200-amp upgrade before most detached ADUs get signed off. We write the panel upgrade as a line item in your original fixed price, not as a door-side surprise after rough-in.
• Hillside-adjacent lots triggering geotechnical review. On the southern and western margins of West Hills where the terrain starts climbing toward the Santa Monica Mountains, LADBS frequently requires a geotechnical report before a detached ADU foundation can be permitted. We identify that risk at the first site visit, not after plans are rejected.
• Rotted sill plates and failed waterproofing on older exterior walls. When we open a 1960s West Hills garage wall to connect a new detached unit or run a utility trench, we commonly find water-damaged sill plates and compromised flashing. We write allowances for these conditions into the contract before work starts, and every change is priced and approved in writing before we proceed.

Pricing for New Detached ADU in West Hills, CA

We Also Serve Cities Near West Hills

Our crews serve West Hills and the surrounding Valley communities. If you’re in West Hills or the nearby areas of Canoga Park, Woodland Hills, Chatsworth, or Northridge, our New Detached ADU team covers your project with the same written-price guarantee and the same local permit knowledge.

FAQs - New Detached ADU in West Hills