ADU Builder & Home Additions in Stevenson Ranch, CA
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Last modified: 2026-09-24T00:00:00.000Z
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Image: Detached backyard ADU with wood siding and black-framed glass doors at dusk
- Stevenson Ranch
Design · Permit · Build
ADUs & Additions in Stevenson Ranch
Detached ADUs, garage conversions and additions, from plans to move-in.
Book a Consultation Call 818-300-2393
Built for Stevenson Ranch Homes
Stevenson Ranch is one of the West Ranch communities of unincorporated Los Angeles County, a master-planned neighborhood west of Interstate 5 and north of Pico Canyon Road that was built out in phases under a plan approved by the County. To the south, Pico Canyon holds Santa Clarita Woodlands State Park and the historic oil town of Mentryville, and the County's area plan notes significant stands of oak trees around West Ranch's developed areas.
With no city government of its own, Stevenson Ranch takes its building permits from County Public Works and its zoning from County Title 22, and inside the Stevenson Ranch HOA an Architectural Committee must approve pools, spas, hardscape and landscaping in writing before work begins.
Fire mapping sets much of the rest of the brief: about four in five single-family lots fall in a Very High Fire Hazard Severity Zone, which brings a County Fire landscape review into new structures and large additions and can narrow the ADU options on those lots.
Master-planned tract homes built out in phases, nearly all between 1987 and 2004 according to LA County Assessor records. Assessor parcel data puts the median single-family lot near 7,800 square feet, with the middle half between roughly 6,300 and 10,000 square feet, and most lots are zoned either RPD (Residential Planned Development) or R-1.
We are a design-build team, which means the people who draw your project are the people who build it. Design, engineering, permits and construction run through one project manager and our own crews, so nothing gets lost in a handoff between a salesperson and a subcontractor. We are licensed, bonded and insured, CSLB license #1119054 .
Permits in Stevenson Ranch: Stevenson Ranch is unincorporated, so building permits come from County Public Works through its Santa Clarita district office on Valencia Boulevard, and zoning follows County Title 22 rather than a city code. About four in five single-family lots fall in a Very High Fire Hazard Severity Zone on the current state maps; there, a new structure, an addition equal to at least half the existing square footage, or certain accessory structures over 120 square feet need a County Fire fuel modification plan approved before the building permit.
Under Title 22 Section 22.140.640, a lot in a Very High Fire Hazard Severity Zone as depicted in the County General Plan can add only a state-exempt ADU, meaning a conversion of existing space or a detached unit of up to 800 square feet with four-foot side and rear setbacks, unless it has two separate, non-overlapping vehicular routes to a highway, each at least 24 feet wide, or fronts a highway with direct vehicle entry.
Within the Stevenson Ranch HOA, pools, spas, hardscape, landscaping and patio covers also need written Architectural Committee approval before work starts.
Permit details checked September 2026 against LA County Planning , Los Angeles County Code and LA County . Rules change, so we confirm them again for your parcel.
What We Build
- HOA Architectural Committee submittals
- Fuel modification landscape plans
- Fire-zone ADU access and size review
- Geotechnical review in mapped landslide zones
- Detached ADUs, ground-up
- Garage conversions to living space
- Junior ADUs within the main house
- Room additions and bump-outs
- Second-story additions
- Full kitchens and bathrooms in the ADU
- Separate utility metering where required
- Private entries, patios and landscaping
- Plans, engineering and city submittals
- Title 24 energy compliance
Local Conditions
What to Know in Stevenson Ranch
These local conditions change the scope, the schedule and the budget.
01
About four in five single-family lots are mapped Very High Fire Hazard Severity Zone and more than nine in ten sit in a fire hazard zone of some severity; where a fuel modification plan applies, its zones out to 30, 100 and 200 feet from each structure, or to the property line, govern planting and layout.
02
More than a quarter of single-family parcels fall inside a state-mapped earthquake-induced landslide zone and about one in ten inside a liquefaction zone on the Newhall and Oat Mountain quadrangles, so soils findings belong at the start of pool and structure design.
03
An oak at least eight inches in trunk diameter, measured four and a half feet above grade, has a County protected zone reaching five feet beyond the dripline or 15 feet from the trunk, whichever is greater; encroaching into it takes an Oak Tree Permit, and approved digging there can be limited to hand tools or small power equipment.
04
In any Fire Hazard Severity Zone a County ADU must sit at least 200 feet from publicly dedicated open space, although the rule still allows a unit of 800 square feet with four-foot side and rear setbacks, which matters on lots that back onto open space.
Areas we serve in Stevenson Ranch:WestridgeDiamondheadMarbleheadPacific ColonyTreana
Investment
What It Costs in Stevenson Ranch
Real Southern California price ranges, not teaser numbers.
Detached ADU
$150,000 to $400,000+
What moves it: square footage, finish level, utility runs, and site access; garage conversions typically run well below a ground-up detached build
Garage conversion ADU
$80,000 to $180,000
What moves it: whether the existing slab and framing meet current code, how far utilities have to run, and the finish level of the kitchen and bathroom
Plans, drawings and permit management
$4,500 to $25,000+
What moves it: project type and size, whether structural engineering, Title 24 or a soils report is required, and how many jurisdictions or review bodies are involved
Your lot, access and finishes set the price. We walk the site, then show you where every dollar goes.
Get a line-item price for your Stevenson Ranch property
The Process
How We Work in Stevenson Ranch
01
Feasibility
We check lot size, setbacks, utilities and access to confirm what your property will actually support.
02
Design & 3D
Layout, elevations and finishes, modeled in 3D so you approve the unit before submittal.
03
Plans & Permits
We prepare the full drawing set, handle engineering and Title 24, and manage the city submittal and corrections. In Stevenson Ranch that submittal goes to Los Angeles County Public Works, Building and Safety Division (Santa Clarita District Office).
04
Foundation & Framing
Site prep, foundation, framing and dry-in by our own crews.
05
Systems & Finishes
Electrical, plumbing, HVAC, insulation, then kitchen, bath and interior finishes.
06
Final Inspection
We pass final inspection, walk the unit with you and hand over the keys.
Questions
What Stevenson Ranch Homeowners Ask
Who issues the permits for this work in Stevenson Ranch?
Los Angeles County Public Works, Building and Safety Division (Santa Clarita District Office). Stevenson Ranch is unincorporated, so building permits come from County Public Works through its Santa Clarita district office on Valencia Boulevard, and zoning follows County Title 22 rather than a city code.
About four in five single-family lots fall in a Very High Fire Hazard Severity Zone on the current state maps; there, a new structure, an addition equal to at least half the existing square footage, or certain accessory structures over 120 square feet need a County Fire fuel modification plan approved before the building permit.
Under Title 22 Section 22.140.640, a lot in a Very High Fire Hazard Severity Zone as depicted in the County General Plan can add only a state-exempt ADU, meaning a conversion of existing space or a detached unit of up to 800 square feet with four-foot side and rear setbacks, unless it has two separate, non-overlapping vehicular routes to a highway, each at least 24 feet wide, or fronts a highway with direct vehicle entry.
Within the Stevenson Ranch HOA, pools, spas, hardscape, landscaping and patio covers also need written Architectural Committee approval before work starts. We prepare the drawings, make the submittal and handle plan-check corrections ourselves, so you are not the one chasing plan check.
What makes building in Stevenson Ranch different?
Master-planned tract homes built out in phases, nearly all between 1987 and 2004 according to LA County Assessor records. Assessor parcel data puts the median single-family lot near 7,800 square feet, with the middle half between roughly 6,300 and 10,000 square feet, and most lots are zoned either RPD (Residential Planned Development) or R-1.
One local condition that shapes the work: About four in five single-family lots are mapped Very High Fire Hazard Severity Zone and more than nine in ten sit in a fire hazard zone of some severity; where a fuel modification plan applies, its zones out to 30, 100 and 200 feet from each structure, or to the property line, govern planting and layout.
Which parts of Stevenson Ranch do you work in?
All of it, including Westridge, Diamondhead, Marblehead and Pacific Colony. Our crews run every job out of our Cahuenga Pass base in Los Angeles, with our own people on site.
What does an ADU or addition cost in Stevenson Ranch?
Detached ADU: generally $150,000 to $400,000+ across Southern California. What moves it is square footage, finish level, utility runs, and site access; garage conversions typically run well below a ground-up detached build. We give line-item pricing after seeing the site rather than quoting a number over the phone.
How long does an ADU take start to finish?
Plan a realistic year. Design and engineering typically take one to three months, city plan check and corrections add several more, and construction usually runs four to eight months depending on size and site access.
Is a garage conversion cheaper than a detached ADU?
Usually yes, and often substantially, because the foundation, walls and roof already exist. The trade-offs are that you lose the garage, and older slabs and framing sometimes need upgrading to meet current code.
Can I rent the ADU out?
California ADU law is designed to allow long-term rental, and an ADU is one of the few ways to add rentable square footage to a single-family lot. Short-term rental rules vary by city, so confirm your local ordinance before counting on that income.
Do you handle the permits?
Yes. Plans, engineering, Title 24 and the city submittal are all handled in-house, including responding to plan-check corrections. That is a service we sell on its own, so it is not something we hand off.
More Services in Stevenson Ranch
Pool & Spa Remodeling in Stevenson Ranch Backyard & Outdoor Living in Stevenson Ranch Everything we build in Stevenson Ranch
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Planning Guides
Before You Build in Stevenson Ranch
Costs, materials and process notes from our own projects.
ADU Cost Breakdown by Size in Los Angeles A detached ADU in Los Angeles runs $150,000 to $400,000-plus. Here is the real cost broken down by unit size, with the soft costs, utility work and finish decisions that move the number. Read guide Garage Conversion to ADU: The Step-by-Step Build A garage conversion runs $80,000 to $180,000 in Southern California. Here is the real sequence, from slab testing and plan check to the raised floor, the mini-split and final sign-off. Read guide ADU Rental Income Math in the San Fernando Valley A one-bedroom ADU in the San Fernando Valley rents for roughly $2,100 to $2,900 a month. Here is the honest arithmetic on payback, carrying costs and what the unit adds to the property. Read guide Second Story Addition vs Building Out: Which Costs Less Building out runs $350 to $500 per square foot. Going up runs $450 to $700. Here is when the cheaper option is actually the wrong one, and what drives each number. Read guide
Planning an ADU in Stevenson Ranch?
Sit down with your project manager and get an accurate estimate. We call you back within one business day.
Book a Consultation 818-300-2393
Licensed, bonded & insured · CSLB license #1119054
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