Detached ADU Construction
A standalone backyard home with its own entry, sited around oaks, slopes and setback lines on Westlake lots of every size.
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ADU contractor, Westlake area
Westlake Village ADU Builder for Both Sides of the Lake
Our team designs, permits and builds accessory dwelling units for homeowners around Westlake Lake, from the City of Westlake Village to the Thousand Oaks and Ventura County neighborhoods that share its mailing address.
4 ftMost a city can require for ADU side and rear setbacks
60Days a city has to act on a complete ADU application
500Square feet: the size cap for a junior ADU
750Square feet: ADUs under this size skip impact fees
California ADU law (Government Code 66310-66342). Coastal, hillside and fire-zone lots can carry extra local rules.
ADU services
ADU Services in Westlake Village
Every unit type below follows the same path: we design it for your specific parcel, secure the approvals from whichever agency governs that address, and build it with our own coordination of trades, inspections and utility hookups. Choose a service to see how it plays out on Westlake lots.
Attached ADU Construction
A unit added onto the side or rear of the main house, sharing a wall but keeping a separate entrance and kitchen.
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Garage Conversion ADU
Turn an attached or detached garage into a legal unit. Inside City limits, LA County's pre-approved garage plan can shorten design.
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Junior ADU (JADU)
Existing rooms inside the house become a compact unit (500 square feet at most) that gets an efficiency kitchen and an outside door of its own.
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Above-Garage and Two-Story ADU
A second-story unit over an existing or new garage, useful where the yard is small or steep and building up beats spreading out.
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Prefab ADU Installation
Factory-built ADUs set on a site-built foundation. We handle the permits, crane access and utility connections a module still needs.
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Multifamily ADU Construction
Added units on condominium and apartment properties under current state rules for detached ADUs and converted storage or garage space.
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ADU Design and Plans
Plans drawn for your parcel and your permitting agency, with HOA review, oak protection and fire hazard rules worked in from the start.
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ADU Permits and Approvals
City Zoning Clearance, LA County plan check through EPIC-LA, or the Thousand Oaks and Ventura County equivalents, tracked to approval.
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ADU Foundations and Utilities
Foundations, grading, sewer laterals, water lines, panel upgrades and fire sprinklers where they are required for the unit.
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ADU Kitchens and Bathrooms
Compact kitchens and full bathrooms planned for small floor areas, with plumbing runs and ventilation sorted out before framing.
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Not sure which ADU fits your lot?
Tell us about the property and what you want the space for. We will reach out and talk through the options that fit your lot and local rules.
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ADU builders in Westlake Village
An ADU Contractor Who Knows Which Westlake Village You Live In
Westlake Village ADU Builder Pros handles a backyard or in-home unit from the first sketch to the final sign-off. We draw the plans, prepare the permit package, coordinate the utility work and build the unit. The work covers backyard cottages, additions that share a wall, converted garages, a JADU made from a spare bedroom suite, second-story units over a garage and factory-built units set on a new foundation.
The first thing we do on any Westlake job is confirm who actually permits the parcel. The address on your mail does not settle it. The incorporated City of Westlake Village sits on the Los Angeles County side of the lake, while much of the original master-planned community lies in Ventura County, inside the City of Thousand Oaks or in unincorporated county land around Lake Sherwood and Hidden Valley. Each of those agencies runs its own ADU process, and the drawings have to match the right one.
See How We Build ADUsADU project types
Westlake Village Lot Types and the ADUs That Suit Them
Below are the unit-and-lot combinations that come up most often across the Westlake area. They describe what tends to fit, not finished jobs. Your lot, your HOA and your permitting agency decide the final answer, and we confirm all three before drawing anything.
Garage Conversion ADU on an Original Westlake Tract Lot
The earliest Westlake streets have single-family homes with attached garages on relatively level lots. Because these parcels sit inside City limits, a garage conversion can start from Los Angeles County's pre-approved standard plan, which trims design time. State law also means the lost garage parking does not have to be replaced.
What is involved:
- Pre-approved plan
- Zoning Clearance
- Slab and insulation
- Egress windows
Detached ADU Among Oaks on a Larger North Ranch Lot
North Ranch lots around the country club are often wide enough for a detached guest unit, but they also carry mature oaks that Thousand Oaks protects. Siting the unit outside root zones and planning trenching around the trees is the main design task, along with HOA architectural review in the gated tracts.
What is involved:
- Oak tree review
- Thousand Oaks permits
- Utility trenching
- HOA review
Attached or Above-Garage ADU on a Sloped Hillside Lot
Southshore Hills homes step down hillsides south of the lake, which leaves little flat yard for a backyard cottage. Building onto the house or over the garage uses the existing pad instead of cutting into the slope. Expect a structural review of the garage, a soils report and attention to fire hazard construction rules.
What is involved:
- Structural design
- Soils report
- Fire-rated materials
- Thousand Oaks permits
Detached ADU With Well and Septic on a Ranch Parcel
Hidden Valley parcels run 20 acres and up, so room is rarely the issue. Water and wastewater are. Homes there rely on private wells, so the ADU's supply has to come from the existing well or a new one, and a septic system must handle the added flow. Ventura County reviews both alongside the building plans.
What is involved:
- Well capacity
- Septic design
- Fire access
- Ventura County permits
Westlake Village ADU Permits: Zoning Clearance, Then an LA County Building Permit
Inside City limits, an ADU needs two approvals in sequence. The City of Westlake Village grants a Zoning Clearance, and Los Angeles County Building and Safety issues the building permit. Under state law, the agency must say within 15 business days whether an application is complete, and must rule on a complete application inside 60 days if a house already stands on the parcel.
How ADU permits work in Westlake VillageThree Stages of a Westlake Village ADU Project
Each project moves through three stages. The order never changes, but what happens inside each stage depends on which agency permits your address and what the lot looks like once we measure it.
01
ADU Plan and Design
We confirm the parcel's jurisdiction, review setbacks, trees, slope and utilities, and check your HOA's architectural rules. Then we draw floor plans and elevations, refine them with you, and prepare the engineering the permit set will need.
02
ADU Permits and Approvals
We submit to the right agency, whether that is the City's Zoning Clearance followed by County plan check, Thousand Oaks, or Ventura County. We answer corrections, track the state review deadlines and keep you posted until the permit issues.
03
Build and Final Inspection
Construction runs from foundation through framing, utilities, insulation, drywall and finishes, with inspections at each required stage. The job closes when the inspector signs off the final and the unit can be legally occupied.
Why build an ADU in Westlake Village
Why an Accessory Dwelling Unit Makes Sense in Westlake Village
Westlake grew up as a planned suburb of single-family tracts, golf course neighborhoods and lakefront lots. That housing stock leaves a lot of room for a second unit: three-car garages, generous side yards on corner lots, and finished bonus rooms that can become a separate home. State law now lets most of these properties add a unit by right, so the question is less about whether you can build and more about what fits your lot.
- Space for aging parents or adult children who want to stay close to Conejo Valley and Las Virgenes schools
- Long-term rental income, since state law bars owner-occupancy requirements for ADUs
- A by-right path: ministerial review, no public hearing, and a state deadline for the decision
- Garage and spare-room conversions that can use LA County's pre-approved standard plans inside City limits
- Added living space without moving out of a neighborhood that rarely has homes for sale
Westlake Village Lots, Jurisdictions and ADU Rules
Inside the City of Westlake Village, an ADU is approved administratively through a Zoning Clearance from the City's planning staff, based on the standards in Municipal Code section 9.14.070. Construction permits then come from Los Angeles County Building and Safety, which the City contracts with. Plan check runs through the County's EPIC-LA online portal, and the local County office is on Agoura Road in Calabasas. Two agencies, two sets of comments, one set of drawings that has to satisfy both.
In February 2026 the state housing department (HCD) wrote to the City noting that the most recent Westlake Village ADU ordinance on file was from 2022 and may not line up with current state law. Where a local rule conflicts with the state statute, the state rule controls. We check the City's current standards during design rather than assume the older ordinance still governs every detail.
Lots across the area vary more than the tidy street names suggest. The flatter tracts near the lake and along the valley floor suit garage conversions and single-story backyard units. Hillside streets south of the lake and in North Ranch bring grading, retaining walls and fire hazard rules. Mature oaks are everywhere, and the City requires a Protected Tree Permit before work affects an oak or a designated heritage tree, so a detached unit is often sited around the canopy rather than through it.
Most Westlake homes also sit under a homeowners association. State law limits how far an HOA can block an ADU, but associations still review exterior colors, roof materials and placement in many tracts. We plan for that review so it does not hold up the permit.
Westlake Village ADU Cost Factors
Prices are not listed here for a reason: identical-size ADUs on neighboring Westlake lots can end up far apart. The type of unit matters most. Converting a garage or an unused part of the house reuses a slab, a roof and walls, while a new detached unit starts from bare ground. Size is next, followed by finish level, the number of bathrooms and how much kitchen you want.
Site conditions are the cost drivers people underestimate. A sloped backyard can need a stepped or caisson foundation, a soils report and retaining walls. A long run from the house to a backyard unit means more trenching for the sewer lateral, water line and electrical feed. An older main panel may need a service upgrade with Southern California Edison before a new unit with its own kitchen can be added. Fire hazard zones add ignition-resistant construction requirements.
Fees are another variable. Under state law, a unit at or below 750 square feet carries no impact fees, and on junior ADUs up to 500 square feet, so keeping a unit under that line can change the budget. Plan check, permit, school and utility connection charges still apply depending on the agency. On the Ventura County side, a well or septic system on a large rural parcel adds its own studies and approvals. We walk through each of these items before you commit to a design.
Westlake Village service areas
ADU Builders Across Westlake Village
We work in First Neighborhood, Three Springs and Lakeshore inside the City of Westlake Village, on Westlake Island where the city line splits the parcels, in Southshore Hills and North Ranch under Thousand Oaks rules, and in Lake Sherwood and Hidden Valley in unincorporated Ventura County. Each area page explains what its lots and permits mean for an ADU.
Westlake Village area
ADU Builder in First Neighborhood
See First Neighborhood
Westlake Village area
ADU Builder in Three Springs
See Three Springs
Westlake Village area
ADU Builder in Lakeshore
See LakeshoreFAQs
Westlake Village ADU Questions
Does my Westlake Village address mean the City of Westlake Village permits my ADU?
Not necessarily. Only the Los Angeles County portion of the original Westlake community is the City of Westlake Village. Many homes with Westlake Village mailing addresses are in the City of Thousand Oaks, and some are in unincorporated Ventura County. We look up the parcel before any design work.
How long do ADU permits take in Westlake Village?
It depends on the agency and how complete the submittal is. The agency owes you a completeness answer within 15 business days, then a yes or no within 60 days of a complete file, as long as a house is already on the lot. Inside City limits, the City's Zoning Clearance comes first and LA County plan check follows, so allow for both steps.
Can I rent out an ADU in Westlake Village?
Yes. Owner occupancy cannot be made a condition of building or renting an ADU. Junior ADUs and units built under the state by-right provisions can only be rented for terms longer than 30 days, and local rules can restrict short stays in other ADUs too. Your HOA may have its own leasing rules, which we suggest you read early.
Does an ADU change my property tax bill?
Generally only the new unit is assessed, and that added value is layered onto what the home is already assessed at. The main house is not reassessed simply because an ADU was built. The county assessor sets the added value, so ask them for specifics on your parcel.
Can my HOA stop me from building an ADU?
State law prevents associations from banning ADUs or junior ADUs outright or imposing rules that make them unreasonably hard to build. An HOA can still apply reasonable architectural standards, such as colors, materials and roof style. We plan the design so it can pass that review.
How close to the property line can an ADU be built?
State law allows a new ADU with side and rear setbacks of four feet. Front setbacks and other local standards still apply in some cases, and an oak tree, an easement or a slope can push the unit further in. We map all of that before choosing a footprint.
Do I need to add parking for an ADU?
At most, one space per unit or one per bedroom (the smaller number) can be required, and tandem spots on a driveway count. No parking is required for a unit created inside the existing house or a garage, and parking lost to a garage conversion does not need to be replaced.
ADU consultation
Start a Westlake Village ADU Consultation
Describe the lot, the house and the job you want the unit to do. We will check who permits your parcel and reach out within 24 hours.
- Design
- Permits
- Construction