Trusted New Detached ADU for Simi Valley Homeowners
A new detached ADU in Simi Valley typically costs $220,000-$450,000 all-in, from permit-ready drawings through final inspection, depending on size, finish level, and whether you build custom or go prefab. Most projects take 8-14 months from signed contract to certificate of occupancy, with the permit phase running 3-6 months through Ventura County and the city of Simi Valley. Ellery ADU Studio has designed, permitted, and built over 900 ADUs since 2015, the year California’s ADU laws shifted, and every project starts with a written price before any work begins.
We’re Nadia Ellery’s design-build studio, independently owned and operated here in Simi Valley. Our crews are background-checked, uniformed, and state-licensed, and our license number appears on every page. We don’t hand you off from an architect to a builder who blame each other when the slab doesn’t match the drawings. One contract, one written price, one team accountable from the first site survey to the final walkthrough. If you’re weighing a detached ADU against a garage conversion, considering a New Detached ADU - Moorpark comparison, or wondering whether a prefab system makes sense for your lot in the Santa Susana foothills, call us at (820) 444-6584. We’ll give you a free estimate with real numbers, and a free second opinion on any written estimate you already have in hand.
What Our New Detached ADU Service Includes
Custom Built ADU
A custom built ADU is stick-framed on your property to your exact specifications, designed from foundation to finish by our in-house team. You need this when your lot has unusual topography, your design vision doesn’t fit a prefab module, or you want materials and layouts that aren’t available in factory-built systems. In Simi Valley, we regularly see custom builds on hillside lots in Wood Ranch and the Santa Susana Knolls, where the grade change and setback requirements demand a site-specific foundation and roofline. Our team produces the full permit set, including structural calcs, Title 24 energy compliance, and landscape integration plans, then builds from that same set so there’s no designer-versus-builder gap.
Prefab ADU Installation
Prefab ADU installation brings a factory-built module to your site, craned onto a prepared foundation and connected to utilities. You need this when speed matters, your lot is relatively flat and accessible, and you want factory precision on finishes and weather sealing. In Simi Valley, prefab works well on the flatter lots near Royal Avenue and the older neighborhoods south of Los Angeles Avenue, where crane access is straightforward and the soil is stable decomposed granite. Ellery coordinates the factory order, site prep, foundation, utility trenching, and final connections under the same single contract, so if the module arrives and the sewer lateral is 6 inches off, it’s our problem to solve, not yours to coordinate between vendors.
Modular ADU
A modular ADU is built in sections at a factory, transported to site, and assembled into a finished structure that meets California’s Factory Built Housing regulations. You need this when you want multi-room layouts or two-story designs that exceed single-module dimensions, or when you need the structural engineering review completed in a controlled factory environment rather than field-verified. We’ve specified and coordinated modular systems from Dvele and Mighty Buildings for Simi Valley clients who wanted two-bedroom layouts with vaulted ceilings and net-zero energy packages. The factory quality control means fewer weather delays and less on-site waste, but the coordination between factory production schedule and site readiness is critical. We manage that timeline in writing, with milestone dates tied to your contract.
Studio ADU
A studio ADU is a single-room detached unit with kitchenette and full bath, typically 300-450 square feet. You need this when your lot is limited on space, your budget is tighter, or you’re building for a single occupant, home office, or rental income stream. In Simi Valley’s older neighborhoods near Simi Hills and the original townsite, we’ve fit studio ADUs onto 5,000-square-foot lots where the rear yard setback leaves only 18 feet of buildable depth. Our permit sets for these projects include space-efficient kitchen layouts that meet CalGreen requirements, wet-wall plumbing clustering to minimize trenching, and exterior finishes that match the primary residence so the unit reads as part of the property, not an afterthought.
1-Bed & 2-Bed ADU
A one-bedroom or two-bedroom ADU adds dedicated sleeping quarters, a separate living area, and full kitchen facilities, typically 500-1,200 square feet. You need this when the unit will house family long-term, serve as a premium rental, or accommodate aging parents who need privacy and space. In Simi Valley, we’ve built two-bedroom detached ADUs in the Sycamore Canyon and Big Sky areas, and a New Detached ADU in Thousand Oaks, for clients whose adult children needed independent housing after buying at peak prices between 2018 and 2022. These projects require careful attention to parking replacement rules under Simi Valley’s municipal code, bedroom egress window sizing, and HVAC zoning for comfort. Our permit set addresses each of these in detail, and our build team constructs from those drawings without deviation.
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.
Brands We Service for New Detached ADU
Ellery ADU Studio specifies and coordinates prefab and modular systems from the leading factory builders, integrated into the same single-contract design-build model that governs all our work. We’ve placed multiple Cover units on Simi Valley lots, managing their steel-frame chassis and integrated MEP systems through Ventura County’s plan check process. Cover’s platform requires precise foundation tolerances, within a quarter-inch, and we prep those pads with laser-level verification and documented photo records at every pour. We’ve also coordinated Dvele’s net-zero modular systems for clients in the Santa Susana foothills who wanted solar-ready roof structures and battery backup integration. Dvele’s factory completion level, including finished interiors and appliances, means the on-site phase is primarily utility connection and final inspection, but the coordination between their production schedule and our site prep timeline is where projects succeed or stall. We lock those dates in writing before either side commits capital.
Our team has worked with Mighty Buildings’ 3D-printed polymer composite panels for studio and one-bedroom configurations, navigating the alternative materials approval process with Simi Valley’s building department. Mighty’s system prints complex geometries that reduce thermal bridging, but the documentation package for plan check is specialized, and we’ve developed that submittal template through direct project experience. We’ve also evaluated Boxabl’s foldable module system for clients with tight access constraints, though we only recommend it where the lot geometry genuinely favors their transport and crane requirements. Whether you arrive with a brand preference or want us to recommend the right system for your lot, soil, and budget, we evaluate it honestly. If prefab doesn’t make sense for your property, we’ll tell you before you spend money on a deposit, and we’ll quote the custom build alternative at the same time.
Signs You Need New Detached ADU Right Now
- Your household needs separate living space that doesn’t exist. Maybe your adult child moved back after buying at a 2021 peak, or you’re expecting aging parents to need ground-floor access within two years. In Simi Valley, where median home prices remain above $700,000, building an ADU is often cheaper than buying a separate property, and it keeps family on the same lot. The longer you wait, the more construction costs tend to rise, and Ventura County’s ADU fee waivers have already sunset for some project types.
- You’re leaving rental income on the table. Simi Valley’s rental market supports $1,800-$2,800 monthly for a permitted one-bedroom ADU, depending on finish level and neighborhood. If you have a flat rear yard sitting unused, that’s a revenue stream you’re not capturing, and California’s ADU laws prevent cities from blocking rental ADUs on owner-occupied lots. The financial case improves with each year of missed rent, and the tax treatment of ADU depreciation is favorable compared to most home improvements.
- Your garage conversion won’t work. Some Simi Valley garages have structural issues, ceiling heights below 7 feet 6 inches, or locations that don’t meet setback requirements for conversion. Others are actively used for parking, storage, or workshop space that the household genuinely needs. A new detached ADU solves these constraints by starting fresh on a different part of the lot, with full design flexibility and no compromise on the existing garage function.
- You need the unit to match a specific design vision. Prefab and modular systems have fixed dimensions, finish palettes, and rooflines. If you want a Spanish Colonial Revival exterior to match your 1980s Wood Ranch home, or a modern flat roof with clerestory windows facing the Santa Susana Mountains, custom design-build is the path. The permit set becomes the blueprint for that vision, and our team builds exactly to those drawings under the 365-Day Done Right Promise.
- Your lot has challenging conditions that rule out simple solutions. Hillside grades, expansive clay soils, oak tree protection zones, or utility easements can make prefab delivery impossible or garage conversion impractical. We’ve designed detached ADUs on Simi Valley lots with 15% slopes, requiring stepped foundations and retaining walls that no factory module could accommodate. These projects demand site-specific engineering, and our in-house team produces that documentation as part of the standard scope.
Our New Detached ADU Process - Step by Step
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Site Survey and Feasibility Study. We visit your Simi Valley property with a survey-grade measuring device, document existing structures and setbacks with a documented photo record, and pull the parcel map and zoning designation from Ventura County records. Within one week, you receive a written feasibility report: what you can build, where it can sit, and what the known constraints are. This report is free and carries no obligation.
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Design Development and Permit Set Production. Our architects produce schematic designs based on your program and budget, then develop the full permit set including floor plans, elevations, sections, structural calculations, Title 24 energy compliance, and landscape plans. For Simi Valley projects, we submit simultaneously to the city planning department and Ventura County building and safety, coordinating any required fire department access reviews or school district impact fees. The permit set is the core product of this phase, and you own it outright.
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Fixed-Price Contracting Under Haven Standard Clause 1. Once the permit set is approved, we issue a written line-item quote covering every phase: site prep, foundation, framing, MEP, finishes, and final inspection. Under Haven Standard Clause 1, this price is fixed before any work begins. No change orders unless you request a scope change in writing. No “discoveries” that inflate the budget mid-project. The scope is locked at signing.
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Construction with Documented Photo Records. Our background-checked, uniformed crews build from the approved permit set, with a project manager on site weekly minimum. Every visit produces a documented photo record, uploaded to your client portal: what was found, what was done, and what comes next. If the foundation pour reveals unexpected soil conditions, you see the photo evidence and our recommended solution before any additional work proceeds.
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Final Inspection and 365-Day Done Right Promise. We walk every finished ADU with you using a punch list tied to the permit drawings, then coordinate final inspection with Simi Valley’s building department. After occupancy, the 365-Day Done Right Promise remains in force: if any element of the finished unit is not built to the permitted drawings, we make it right, in writing, with a response timeline specified in your contract. This is not a handshake. It’s Haven Standard Clause 7, signed before construction starts.
How Much Does New Detached ADU Cost in Simi Valley?
For a sense of overall investment, see our New Detached ADU cost guide; a typical studio ADU in Simi Valley runs $220,000-$290,000 all-in, drawings through final inspection. A one-bedroom unit typically runs $280,000-$360,000. A two-bedroom detached ADU, or a custom design with premium finishes, typically runs $350,000-$450,000. Prefab and modular systems can land at the lower end of these ranges for standard configurations, but site conditions, foundation requirements, and utility trenching lengths often narrow that gap.
Several factors move the price within these ranges. Soil conditions matter: Simi Valley’s decomposed granite is generally stable, but hillside lots in Wood Ranch or the Santa Susana Knolls may require engineered fill or retaining walls that add $15,000-$40,000. Utility distance is significant; if your sewer lateral is 80 feet from the proposed ADU location, trenching and connection run higher than a 20-foot span. Finish level affects the interior budget substantially, with appliance packages, flooring, and cabinetry representing 15-20% of total cost. Roof complexity, second-story construction, and covered parking requirements also shift the number.
What affects the price most is the design-build integration. When architects and builders operate separately, the builder’s field conditions force redesigns that cost time and money. Our single-contract model eliminates that friction. The permit set is produced by the same team that builds from it, so the foundation dimensions match the module specs, the window openings align with the structural headers, and the electrical panel location accounts for the actual trenching path. This coordination is why we can offer a written price before work starts and stand behind it.
To avoid overpaying, compare written estimates line by line, not just bottom-line totals. One quote that seems lower may omit permit fees, utility connection costs, or the final inspection phase. Our estimates include every known cost, and we flag contingencies separately with a dollar cap. The free estimate includes a written scope, a proposed timeline, and a clear explanation of what is fixed and what is variable. Call (820) 444-6584 to schedule yours.
New Detached ADU Near Simi Valley - Our Service Area
Ellery ADU Studio builds detached ADUs throughout Ventura County and the west San Fernando Valley, with regular project volume in Moorpark, West Hills, Agoura Hills, Chatsworth, Thousand Oaks, Canoga Park, Calabasas, Winnetka, Northridge, Tarzana, and Reseda. From our Simi Valley base, typical drive time to Moorpark or West Hills is under 20 minutes, and we schedule site visits across this radius without travel surcharges. Each city has distinct ADU ordinances, setback requirements, and fee structures, and our permit sets are customized to the specific jurisdiction rather than templated. Whether your lot is in the Simi Valley proper or in a neighboring community with different parking replacement rules, we produce documentation that passes plan check the first time.
Serving Simi Valley, CA - Our Local Coverage Area
We’re based in the Simi Valley area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
Frequently Asked Questions - New Detached ADU in Simi Valley
A new detached ADU is a separate, ground-up residential structure built on your property, not connected to your main house, while a garage conversion repurposes an existing garage into living space. Detached ADUs offer full design flexibility, separate utility metering, and no loss of garage function, but they typically cost more and require more site work. In Simi Valley, detached ADUs are permitted under both state law and local ordinance, with specific setback and height limits that vary by zoning district. Call (820) 444-6584 for a free feasibility study on your lot.
Most new detached ADUs in Simi Valley take 8-14 months from signed contract to certificate of occupancy, with design and permitting representing 3-6 months and construction 5-8 months. Prefab and modular systems can compress the construction phase by 1-2 months, but the permitting timeline remains similar because the same plan check and inspection sequence applies. Delays most often come from incomplete permit submittals or utility coordination issues, which our single-contract model is designed to prevent. Call (820) 444-6584 for a timeline specific to your project type and lot conditions.
A new detached ADU in Simi Valley typically costs $220,000-$450,000 all-in, depending on size, construction type, and site conditions. Under Haven Standard Clause 1, your price is written and fixed before any work begins, with no change orders unless you request a scope change in writing. We separate known costs from contingencies, cap the contingency amount, and document every assumption that underlies the quote. Call (820) 444-6584 for a written estimate with real numbers.
Yes, we specify and coordinate Cover, Dvele, Mighty Buildings, and other prefab and modular systems within the same single-contract design-build model. Our team has direct project experience with each brand’s foundation tolerances, utility connection requirements, and plan check documentation, so we can evaluate whether a given system fits your lot and budget honestly. If prefab doesn’t make sense for your property, we’ll say so and quote the custom alternative at the same time. Call (820) 444-6584 to discuss which construction method fits your project.
We offer a free second opinion on any written estimate you already have in hand, with no obligation to hire us. We’ll review the scope line by line, identify omissions or assumptions that could affect your final cost, and explain where our approach differs. This service exists because many Simi Valley homeowners receive estimates that understate permitting costs, omit utility connection fees, or assume site conditions that haven’t been verified. Call (820) 444-6584 to schedule your free second opinion.
Every new detached ADU is backed by our 365-Day Done Right Promise: if the finished unit is not built to the permitted drawings, we make it right, in writing, with a response timeline specified in your contract. This is Haven Standard Clause 7, agreed to before construction starts, not a vague post-completion offer. We also carry general liability and workers compensation insurance, and our state license number appears on every page for verification. Call (820) 444-6584 for a copy of the Haven Standard terms.
Gather your property’s assessor parcel number, any existing survey or plot plan, and a rough sense of your budget range and intended use, rental income, family housing, or home office. We’ll handle the zoning research, setback calculations, and feasibility analysis from there. If you have inspiration images or specific finish preferences, bring those too, but they’re not required for the initial consultation. Call (820) 444-6584 to schedule your free estimate, and we’ll send a brief preparation checklist in advance.
Schedule Your New Detached ADU Service in Simi Valley Today
Call (820) 444-6584 to schedule your free estimate for a new detached ADU in Simi Valley. You’ll receive a written feasibility report, a line-item quote with a fixed price before any work begins, and a clear timeline from permit set to final inspection. A live person answers calls 24 hours a day, and we offer a free second opinion on any written estimate you already have. There’s no obligation, no deposit required to receive the quote, and no designer-versus-builder gap to navigate. One contract, one written price, one team accountable from start to finish.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Simi Valley since 2015.