A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateFast, Reliable ADU Builders Across Simi Valley
Adding an ADU in Simi Valley usually costs $180,000 to $420,000 for a detached unit, while garage conversions run $120,000 to $280,000 before permit fees. Those are real working numbers for this market, not national averages. Our ADU Builders team knows Simi Valley’s housing stock well: single-family homes built between 1960 and 1990, many on large lots with attached two-car garages. We also know what hides inside those walls, because we have opened enough of them. Call (805) 309-3020 for a free estimate and we will walk your lot with you before anything gets priced.
Why Fielding ADU Thousand Oaks Is Simi Valley’s Preferred ADU Builders Company
We are an independently owned member of the Garrison Partners family, and we build additions and ADUs to a standard most Simi Valley homeowners have never seen put in writing. That standard is simple: a written price before any work starts, permits pulled by the book, and a one-year written guarantee on the completed job. Reed Calloway runs Fielding ADU Thousand Oaks, and he signs off on every project we take in Simi Valley.
The Garrison Code is how our crews operate on every Simi Valley job: show up in the window, price in writing, build by the book, leave it clean, stand behind it for a year. No allowances that balloon. No framing opened and then left exposed while the quote “gets revised.” Homeowners here have dealt with enough of that. We hand you the number before we drive a nail, and the number on your final invoice matches the number you approved on day one.
JADU in Simi Valley
A JADU in Simi Valley is a junior accessory dwelling unit, typically a 150 to 500 square foot conversion carved out of an existing home: a garage bay, a spare bedroom with its own entrance, or a den that shares a wall with the main house. Simi Valley homeowners pursue JADUs when an attached single-car garage on an east side tract home is too tight for a full ADU but still large enough for an efficiency unit with a kitchenette and its own bath. A JADU here typically runs $85,000 to $160,000 depending on foundation condition, plumbing runs, and whether the electrical panel needs upgrading.
Garage Bay JADU Conversions
Many Simi Valley homes built in the 1960s and 1970s have oversized two-car garages with a tandem bay. Converting that third bay or a sectioned-off portion into a JADU costs less than pouring a new slab and framing a detached unit. The catch is the existing slab and the wall framing, which we inspect before quoting. A slab without rebar does not kill the project; it just changes the scope and the number on the page.
JADU With Separate Entrance
The Simi Valley planning department allows JADUs with their own exterior door, which changes how the unit feels for a tenant or family member. We frame the new opening, weatherproof it, and match the existing exterior finish. If the home has Mediterranean styling with stucco, we patch and blend to match; if it is ranch-style with wood siding, we use primed trim that takes paint the same way.
ADU Plans in Simi Valley
ADU Plans in Simi Valley means a full architectural drawing set sealed for permit submission, including site plan, structural calcs, title 24 energy compliance, and the fire-resistance details the city reviews because of Santa Ana wind exposure. A complete plan set for a Simi Valley detached ADU typically runs $6,000 to $12,000; a garage conversion plan set runs $4,000 to $8,000. We do not hand you a folder of concepts and tell you to figure out the rest. We deliver plan sets that Simi Valley’s counter staff will actually accept.
Sealed Drawings and Permit Submission
When we prepare ADU Plans for a Simi Valley project, we walk the lot, measure the existing structure, and check the city’s current ADU ordinance against what you want to build. Setback variance (the city’s written permission to build closer to the property line than the standard rule allows) is a real document, and we pull it when needed rather than skipping it and hoping the inspector does not notice. Plans go in with the permit application, and we stay on top of plan-check comments so the review does not stall.
Structural Calcs for Older Simi Valley Homes
East side Simi Valley homes on original concrete slabs without rebar need structural engineering before a second story goes over the garage. That calc package is part of the plan set, not an add-on we spring on you later. A neighboring Thousand Oaks home built in 1995 might not need it. A Simi Valley home built in 1965 very often does. We tell you that at the first walkthrough, before the plan set gets drafted, so you are pricing the real job.
Trusted Brands We Service in Simi Valley
We install and finish ADUs built on major prefab and modular platforms, including Abodu, Cover, and Dvele, and we also do conventional builds using James Hardie siding. When a Simi Valley homeowner wants a faster path than stick framing, a prefab unit from Abodu or Dvele can cut months off the schedule. We handle the site work, foundation, utility connections, and the finish details that the factory does not. For conventional builds, James Hardie plank holds up to the dry heat and Santa Ana conditions better than wood lap siding, and we have crews who install it daily.
Common ADU Builders Problems We See in Simi Valley Homes
- Original slab foundations without rebar. Many east side tract homes sit on concrete slabs poured without reinforcing steel. Adding a second-story ADU above the garage triggers mandatory seismic retrofitting, and an honest quote includes it from the start. A dishonest one adds it after demo when you have no leverage.
- Undersized or termite-damaged framing. Simi Valley’s dry climate does not stop termites, especially in older wood-frame homes near the open hillsides along Madera Road. We regularly find sill plates and headers that looked fine behind drywall and could not carry a second story once exposed.
- Aluminum branch wiring and undersized panels. Homes built between 1960 and 1975 in Simi Valley often have aluminum wiring or 100-amp panels. A new ADU with a kitchenette, mini-split, and water heater will not pass with that panel. The code upgrade is mandatory, and our contracts carry a written electrical allowance so the permit does not stall when the electrician opens the panel.
- Water intrusion from dry-rot framing around garage doors. Simi Valley gets most of its rain in a few winter months, and the areas around old garage door openings are common failure points. When we convert a garage to a JADU, we open the wall, check the sill plate, and replace anything rotted before insulation goes in.
Pricing for ADU Builders in Simi Valley, CA
Here are the working ranges for Simi Valley:
- Detached ADU (1 bed, 1 bath, 600 – 800 sq ft): $180,000 – $420,000
- Garage conversion to ADU (400 – 600 sq ft): $120,000 – $280,000
- JADU (150 – 500 sq ft, attached): $85,000 – $160,000
- Second-story ADU over garage (500 – 800 sq ft): $200,000 – $450,000, including seismic work on the existing slab
- ADU Plans, sealed for permit: $4,000 – $12,000
What moves the number in Simi Valley: slab condition and seismic retrofitting, electrical panel age and capacity, fire-resistant exterior requirements, and whether the lot allows a detached unit under current setback rules. We price in writing before any work starts, and the figure you approve is the figure on the final invoice. Call (805) 309-3020 for a free estimate on your specific lot.
We Also Serve Cities Near Simi Valley
Our crews serve Moorpark, Oak Park, Thousand Oaks, and Westlake Village as well. If you are in one of those cities and have questions about an ADU, garage conversion, or room addition, the same written-price policy and one-year guarantee apply. Call (805) 309-3020 and we will schedule a walkthrough.
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.
FAQs About ADU Builders in Simi Valley
Yes, if the existing slab has no rebar, Simi Valley’s building code requires seismic retrofitting before a second-story ADU is added above the garage. A single-story garage conversion on the existing slab usually does not trigger the same requirement, but if you add height or a second level, the retrofit goes into the structural calcs and the permit set. We include that cost in the written quote before we start, not after demo. Call (805) 309-3020 and we will check your foundation before you commit to a number.
Yes, many Simi Valley homes have oversized two-car garages with a tandem bay, and the city allows a partial conversion as long as the remaining space still meets the minimum parking requirement. We section off the bay with a fire-rated wall, add a separate entrance, and leave the rest of the garage for storage or a vehicle. The exact layout depends on your home’s dimensions and where the existing garage door sits. Call (805) 309-3020 and we will measure your garage and tell you what fits.
Probably not. Most Simi Valley homes from the 1960s and 1970s have 100-amp panels, and a new ADU with a mini-split, kitchenette circuit, water heater, and lighting will exceed that. Our contracts include a written electrical allowance for panel replacement and branch wiring, so the cost is in the quote from day one. If we open the wall and find aluminum wiring, we photograph it, send you a change order, and get your written approval before any new material goes in. Call (805) 309-3020 for a free estimate.
Yes, Simi Valley’s wildfire-prone hillside areas and Santa Ana wind exposure mean the city’s plan-check staff will require fire-resistant exterior materials, ember-resistant vents, and sometimes a Class A roof assembly on the ADU. For detached units, James Hardie plank or stucco are common approved choices. We build to the stricter standard regardless of your exact zone, because the Santa Ana season here does not care where the property line ends. Call (805) 309-3020 for a walkthrough and we will tell you what your lot actually triggers.
We write a repair allowance into the contract before we open the first wall. That allowance covers framing repair, termite-damaged sill plate replacement, and the electrical work that older Simi Valley homes so often need. On a 1970s ranch near Madera Road, our crew opened a garage wall to convert it into an ADU and found original knob-and-tube wiring hidden behind drywall, plus termite-damaged sill plates along the foundation. Because our contract had a written allowance for electrical replacement and framing repair, we shot photos, sent a change order for approval, and had the new JADU insulated and drywalled in four weeks. That is how the job is supposed to go. Call (805) 309-3020 to schedule your free estimate.
Written by Reed Calloway, Owner at Fielding ADU Thousand Oaks, serving Simi Valley homeowners with written-price ADU construction and garage conversions.
