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 detached ADU, with garage conversions landing between $30,000 and $80,000. Those numbers shift fast once you factor in Simi Valley’s hillside fire-zone codes, 1960s tract-home foundations, and the reality of opening up walls that haven’t been touched since the Carter administration. If you’re planning a second-story addition off the 118 or a garage conversion in 93063, call Barrett & Sons at (877) 610-1318 for a free estimate and a written scope before you commit to anything.
We’re Home Additions & ADU contractors who have spent years working the tract-home stock that defines Simi Valley, from Wood Ranch to the flats east of Tapo Canyon Road. Our crews know which neighborhoods sit on compacted fill, which hillside parcels trigger WUI Chapter 7A requirements, and why a foundation inspection belongs at the front of your scope, not after the slab cracks. Tom Barrett and his sons run the crews themselves, and every price change arrives in writing before a single nail moves.
Why Barrett & Sons Construction Is Simi Valley’s Preferred Home Additions & ADU Company
We founded Barrett & Sons Construction in 1998, and we have been owner-operated from day one. Tom Barrett puts his name, address, and license number on every contract. You can look it up yourself before you sign, and when you call (877) 610-1318, a live person answers, 24/7. Not a voicemail box, not an out-of-state call center.
Simi Valley homeowners tell us the same story over and over: they got a phone quote from a national outfit, then a different bill at the door. That doesn’t happen with us because every scope, every allowance, and every price change is a written change order issued before work proceeds. The permit inspector works for you, not for us, and that’s exactly why we pull permits on every eligible job and stand there while the inspection is signed.
Our work in Simi Valley is backed by the 90-Day Done Right Promise, written on every contract. If something isn’t done right, Tom comes back and makes it right, one call. He lives twenty minutes away. If something’s wrong, he wants to know about it.
Our Home Additions & ADU Services in Simi Valley
ADU Design & Permitting
An ADU in Simi Valley isn’t a shed with a sink. Depending on your parcel, you may be dealing with WUI fire-hardening requirements, hillside grading reviews, sewer lateral upgrades, and the city’s standard plan-check queue. We handle design and permitting as one package, so the drawings match what the inspector will actually sign off on. In the hillside zones north of the 118, that means ember-resistant vents and Class A roofing specified from the first draft, not bolted on after a plan-check rejection.
Garage Conversion ADU
Garage conversions in Simi Valley’s 93063 zip code run $30,000-$80,000, and the single biggest variable is the slab. Many of these 1970s garages were poured on compacted fill that has settled unevenly, so we order a foundation evaluation before we frame a single interior wall. Converting a Larwin-built garage on a cracked slab without addressing the soil movement underneath means cracked tile and binding doors within two years. We’d rather tell you before you pay for drywall.
New Detached ADU
New detached ADUs in Simi Valley land between $90,000 and $220,000, depending on size, site access, and whether the lot sits in a High or Very High Fire Hazard Severity Zone. Hillside parcels near Wood Ranch and the Knolls often require ignition-resistant siding, ember-rated vents, and non-combustible decking that add real cost but are absolutely not optional. We write those allowances into the contract up front, in dollars, not vague percentages.
Junior ADU & Interior Conversion
A junior ADU, often carved out of an existing bedroom or bonus room, is the fastest path to rental income in Simi Valley without touching the roofline. These projects still need permits, a separate entrance, and a kitchenette that meets state standards. We scope them the same way we scope a full addition: inspection first, written allowances for what we find behind the drywall, and every surprise priced in writing before it changes your budget.
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 don’t install mystery materials off the back of a van. On Simi Valley additions and ADU hardscape tie-ins, we carry Belgard and Techo-Bloc pavers, which hold up to the valley’s summer heat better than bargain concrete. We stock Cambridge Paver products for customers who want a specific color match to their existing patio. When we quote a material, you can look it up, compare it, and know exactly what’s going on your property. That’s the point.
Common Home Additions & ADU Problems We See in Simi Valley Homes
- Compacted fill and expansive clay under east-end slabs (93063). Homes built during the 1963-1985 build-out were often graded fast, and the fill has spent fifty years settling. We regularly see slab cracking, door-frame racking, and driveway heaving that has to be addressed before an addition can bear load.
- WUI Chapter 7A fire-hardening triggers on hillside parcels. An addition or ADU north of the 118 can pull in full roof replacement, ember-resistant vent retrofits, and non-combustible siding requirements that a standard tract-home quote from outside the valley won’t include. We price them because we know they’re coming.
- Outdated wiring and failed waterproofing hidden behind stucco. Simi Valley’s original composition shingle roofs and stucco-over-wood construction hide decades of water intrusion and electrical work that was code-compliant in 1972 and isn’t anymore. A “structural” scope without written, line-item allowances becomes a dispute factory at inspection sign-off.
- Santa Ana wind damage to roofs and flashing. Simi Valley sits in an inland bowl that funnels some of the highest recorded wind speeds in the LA metro. Loose flashing and wind-driven ember intrusion aren’t cosmetic issues here. They’re life-safety issues during fire season, and they change how we detail additions and ADU roof connections.
Pricing for Home Additions & ADU in Simi Valley, CA
Here’s the honest range for Simi Valley’s market. No phone-quote games, no “well, it depends” without numbers attached.
| Project Type | Simi Valley Price Range |
|---|---|
| Home Addition | $45,000-$130,000 |
| ADU Construction | $90,000-$220,000 |
| Garage Conversion | $30,000-$80,000 |
What moves the number? Foundation condition on the original graded pads, whether your parcel triggers WUI Chapter 7A upgrades, the size of the addition, and what we find when we open the walls. We handle surprises the way Simi Valley homeowners tell us they wish their last contractor had: an allowance that isn’t on paper is a surprise waiting for a date. Call (877) 610-1318 for a free estimate and a written line-item quote. No change happens without a written change order first.
We Also Serve Cities Near Simi Valley
Our crews serve Simi Valley and the surrounding communities, including Oak Park, Moorpark, Thousand Oaks, and West Hills. If you’re just over the line in Ventura County or just across the hill, the same owner-operated crew shows up, the same written change order policy applies, and the same 90-Day Done Right Promise stands.
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
A grading evaluation is required on many Wood Ranch hillside lots because much of the original 1970s pad grading placed homes on compacted fill that has settled unevenly since construction. You can’t design a second-story addition on a foundation where one corner has dropped two inches and the other hasn’t moved. We pull the grading records, order a foundation inspection, and if the soils report calls for steel pier underpinning, that goes into the contract as a written change order before any framing starts. Call (877) 610-1318 if you’re planning a second story on a hillside lot, and we’ll walk the property with you.
WUI Chapter 7A compliance typically extends to the primary home’s roofing assembly, vents, and siding, not just the new structure. If your existing home has a wood shake or standard composition roof, plan on a Class A reroof. You’ll also need ember-resistant attic vents, ignition-resistant siding or stucco, and non-combustible decking on any new deck or balcony. These upgrades add real cost, so we write them into the initial scope rather than discovering them at plan check. Call (877) 610-1318 for a free estimate that includes a WUI compliance review.
We inspect first, write allowances into the contract, and stop work to price any surprise in writing before we touch it. When we open a 1968 stucco tract home and find aluminum wiring or rotted sill plates, you get a written change order with line-item costs and an explanation of what the inspector will require. Nothing happens without your signature. That’s how Tom Barrett has run jobs since 1998, and it’s why Simi Valley customers who got burned by phone-quote contractors call us the second time.
Often, yes. Garages in the 93063 zip code are frequently built on slab-on-grade foundations poured over compacted fill that has settled and cracked over decades. If the slab has moved, framing interior walls on it means cracked tile, binding doors, and water intrusion within a couple of years. We order a foundation evaluation before we commit to framing, and if the slab needs repair or replacement, it goes into the contract as a written line item. Call (877) 610-1318 to schedule a garage conversion estimate that includes a foundation check.
A draw schedule is a written payment plan that ties your money to completed, inspected work. For a Simi Valley home addition, that typically means payments tied to foundation, rough framing, rough electrical and plumbing, insulation and drywall, and final inspection. The city requires multiple inspections along the way, and your draw schedule means you’re not paying for work the inspector hasn’t approved. We put the draw schedule in writing on every contract, so there’s never a surprise invoice at the end. Call (877) 610-1318 and Tom or one of his sons will walk you through exactly how it works for your project.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Simi Valley and surrounding Southern California communities since 1998.