Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Simi Valley
Home additions and ADU construction in Simi Valley typically run $45,000-$130,000 for a room addition and $90,000-$220,000 for a full detached ADU, with garage conversions landing between $30,000-$80,000. Those numbers reflect what it actually costs to build in this city, because Simi Valley’s 1960s-1980s tract housing brings specific conditions to every job: compacted fill, WUI fire-code requirements, and aging stucco-over-wood framing. We’re Barrett & Sons Construction, and we’ve been opening up Simi Valley walls long enough to know what’s behind them before the first permit gets pulled. Call (877) 610-1318 for a free estimate, and we’ll walk your property with you.
Why Barrett & Sons Construction Is Simi Valley’s Preferred Home Additions & ADU Company
Tom Barrett founded this company in 1998, and he still answers his own phone. That matters in Simi Valley, where homeowners have been burned by outfits that quote one price on the phone and show up with another. Our Home Additions & ADU team works under Tom’s name, which is published right next to his license number. Look it up before you sign anything. We’d want you to.
We’re not a franchise dispatching strangers to Simi Valley. Tom’s sons run the crews, and they’re on-site most days. When you call about a second-story addition in the Wood Ranch hills or a garage conversion off Erringer Road, the person who picks up knows the project. Every scope, every allowance, every price change arrives as a written change order before work happens. That’s not a tagline; it’s how Tom has operated for 29 years.
Simi Valley customers also get our 90-Day Done Right Promise, written on every contract. If something isn’t right, one call brings Tom back. No fine print. No voicemail maze. Just a live person, 24/7, at (877) 610-1318.
Our Home Additions & ADU Services in Simi Valley
ADU Design & Permitting
We handle the full design and permitting path for ADUs in Simi Valley, including the Chapter 7A WUI fire-hardening requirements that apply to hillside-adjacent parcels. If your lot sits north of the 118 or backs up to canyon open space, your ADU plans will need ember-resistant vents, specific roofing assemblies, and fire-rated siding. We draw it right the first time so the plan checker doesn’t bounce it back twice.
Garage Conversion ADU
Converting an attached or detached garage in Simi Valley’s 93062 and 93063 neighborhoods is often the fastest path to rental income or a family suite. But before framing starts, we verify the existing footing. Many of these garages were built on slabs poured decades ago without rebar or proper compaction. Skipping that check causes deflection and drywall cracks within a year. We don’t skip it.
New Detached ADU
A new detached ADU on a Simi Valley lot means running utilities, grading, and setting foundations on soil that ranges from rocky outcroppings to settled fill. We handle site prep and utilities in-house, so you’re not juggling three contractors. And every permit gets pulled. The inspector works for you, not for us, which is exactly why we want him on the job.
Junior ADU & Interior Conversion
A junior ADU inside your existing Simi Valley home is the most affordable way to add a legal dwelling unit, typically by converting a bedroom, bonus room, or attached garage wing. In older tract homes in the east end of the valley, this often means addressing slab cracks, door-frame racking, and outdated wiring before the conversion is code-compliant. We scope it, allow for it in writing, and keep you posted on every change before it happens.
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 Simi Valley
We carry premium brands across the trades because you should be able to look up what’s going into your home. On additions and ADUs in Simi Valley, that means materials like Techo-Bloc for hardscape transitions and Oldcastle for retaining and drainage work where your new foundation meets the slope. We don’t install mystery brands off a van. If a brand name isn’t one you can verify, it doesn’t go on your job.
Common Home Additions & ADU Problems We See in Simi Valley Homes
- Compacted fill settlement. Much of Simi Valley’s hillside tract housing was built on fill pushed from pad grading in the 1960s and 1970s. That fill settles unevenly, which is why we do foundation and grading evaluations before any structural work on lots that back up to canyon grades.
- WUI fire-code triggers. Homes in the High and Very High Fire Hazard Severity Zones, especially north of the 118, must meet Chapter 7A standards when an addition or ADU changes the building envelope. That means ember-resistant vents, specific siding materials, and fire-rated deck construction. It’s a life-safety issue in this valley, not a formality.
- Failed waterproofing on west-facing elevations. On a 1972 Larwin-built tract home in the Wood Ranch hills, we opened a wall for a second-story addition and found the original stucco-over-wood framing had failed waterproofing at the west elevation, with dry rot traveling down the load-bearing king studs. Our crew scoped the damage, wrote a change order for reframing and a WUI-compliant ember-resistant vent upgrade, and got inspection sign-off before closing. The homeowner saw exactly what changed and why before we touched the structure.
- Slab cracking in the east end. Older homes in 93063 frequently show slab cracks, door-frame racking, and driveway heaving tied to the original grading. Adding a room over a slab that’s already moving means the new footprint follows the settled grade and the door racks within a year unless you address the foundation first.
Pricing for Home Additions & ADU in Simi Valley, CA
Here’s what we quote in Simi Valley for the most common projects:
| Project | Typical Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What moves these numbers in Simi Valley specifically: whether your parcel falls inside a WUI zone, the condition of your existing foundation, and how much grading work the lot requires. We write every allowance into the contract up front. If we find something inside the wall that wasn’t on the scope, you get a written change order with a price before we touch it. Call (877) 610-1318 to schedule a free estimate. We’ll give you a written line-item quote, no vague ranges, no surprise invoices.
We Also Serve Cities Near Simi Valley
Our crews work throughout the Conejo Valley and surrounding areas, including Simi Valley and the nearby communities of Oak Park, Moorpark, Thousand Oaks, and West Hills. If you’re just over the grade in Moorpark or up in Thousand Oaks, the same crew, same written change orders, same 90-Day Done Right Promise applies.
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 - Home Additions & ADU in Simi Valley
Your addition must comply with California Building Code Chapter 7A WUI standards, which govern roofing assemblies, ember-resistant vents, siding materials, and deck construction. That means specific materials and installation details that don’t apply to homes in the flatlands of Moorpark or Thousand Oaks. We scope these requirements into the permit drawings from day one, so the plan check goes through without rework. Call (877) 610-1318 and we’ll tell you exactly which WUI measures apply to your specific Simi Valley parcel.
Yes, but the foundation has to be evaluated before any ADU work starts. Slab cracking and door-frame racking in the east end of Simi Valley usually point to settlement from the original grading, not a structural failure. We assess the existing foundation, scope any needed repairs or reinforcement, and write that into the contract before we pull permits. Adding load to a slab that’s already moving will only make it worse, so we don’t skip this step. For an exact quote on your property, call (877) 610-1318.
For 1960s-1980s tract homes in Simi Valley, we recommend budgeting 10-15% of the total project cost as a contingency allowance for conditions you can’t see until the wall is open: outdated wiring, undersized framing, failed waterproofing, or dry rot. The key is that every dollar of that allowance arrives as a written change order before we spend it. An allowance that isn’t on paper is a surprise waiting for a date. That’s why we write the allowance into the contract up front and price every discovery in writing before work proceeds. Call (877) 610-1318 for a free estimate and we’ll walk you through a realistic allowance for your specific home.
Yes. Any legal junior ADU in Simi Valley requires a building permit, and the conversion must meet current code for egress, ventilation, and fire separation. Skipping the permit means you don’t have a legal dwelling unit, which becomes a problem when you sell or if an insurer asks questions. We pull permits on every eligible job and we’ll never tell you permits are optional. That’s the kind of thing the last contractor told people. Call (877) 610-1318 to get your JADU permitted and built properly.
Santa Ana winds hit Simi Valley hard, with some of the highest recorded gusts in the LA metro. That means second-story additions here need heavier framing connections, lapped flashing sealed against wind-driven rain, and ember-resistant vent detailing on every attic penetration. We over-build the flashing because the wind will find any gap. We frame to meet or exceed the local wind design loads, and we use WUI-rated vents on every opening that faces the open space. Call (877) 610-1318 and we’ll explain what this means for your specific addition.
What Actually Happens Inside Simi Valley’s Tract Walls
Here’s what we know from opening up hundreds of 1960s-1980s Simi Valley homes: the wiring is outdated, the waterproofing has failed somewhere, and the original grading left compacted fill that settled unevenly under the slab. A generic remodel template doesn’t account for any of that. Before we start any addition or ADU in Simi Valley, we do an inspection first, then we write allowances into the contract for what that inspection turns up. Any surprise gets priced and approved in writing before we touch the structure. That’s how you avoid the quote that moves. That’s how Tom Barrett has done it since 1998.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Simi Valley and the surrounding communities.