New Detached ADU Cost - Design, Permits and Build Under One Contract

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How Much Does New Detached ADU Cost in Woodland Hills?

A new detached ADU in Woodland Hills typically costs between $220,000 and $420,000 in 2026, with most homeowners landing in the $275,000 to $350,000 range for a 600 to 900 square foot unit. That includes design, permits, site work, construction, and a standard finish package. Prefab and modular options from brands like Abodu or Boxabl can bring the lower end down to about $180,000, while a fully custom 1,200 square foot two-bedroom ADU with premium finishes pushes past $450,000.

These numbers come from the bids we write every month for homeowners across Woodland Hills, from the flat streets south of Ventura Boulevard up into the hills where site conditions change everything. If you want a number for your specific lot, call (559) 249-3776 and we’ll walk the property and write you a real price before any work starts.

Key Takeaways

• Most Woodland Hills detached ADUs cost $275,000 to $350,000 all-in for 600-900 sq ft.
• Prefab ADUs from Abodu, Cover, or Boxabl typically run $180,000 to $280,000 including site work.
• Sloped lots in the hills south of Mulholland Drive add $25,000 to $60,000 in foundation and retaining costs.
• Permits in Los Angeles take 4-9 months and cost $8,000 to $18,000 depending on scope and plan check corrections.
• Every Seedling project gets a written price before work starts and is backed by the 365-Day Done Right Promise.

If you’re weighing a detached ADU against a garage conversion, this guide focuses on new construction. See our New Detached ADU in Woodland Hills page for the full process, or keep reading for line-by-line pricing.

New Detached ADU Cost Breakdown (2026)

Here’s what a new detached ADU actually costs in Woodland Hills when you break it into the pieces a builder prices. These are real ranges from bids written for local lots in 2026, not national averages.

Add those up and you’ll see why the honest range for Woodland Hills is $220,000 to $420,000. Anyone quoting below $180,000 for a new detached ADU on a flat lot is either leaving out permits, quoting a bare-bones shell, or planning to surprise you with change orders.

What Pushes the Price Up or Down

The two biggest cost drivers in Woodland Hills are lot slope and finish level. A 650 square foot one-bedroom on a flat lot south of Oxnard Street with standard finishes is a $260,000 project. Put that same ADU on a steep hillside lot above Mulholland and add a second bedroom, custom cabinets, and upgraded flooring, and you’re at $380,000 before you blink. Soil conditions matter too: some pockets of Woodland Hills sit on expansive clay that requires deeper footings, and a few hillside lots need caissons, which add $15,000 to $40,000 on their own.

Prefab changes the math. Working with Abodu, Cover, Dvele, Mighty Buildings, Boxabl, or Plant Prefab usually removes most framing and finish costs from the site-built side of the ledger. A prefab ADU from Abodu on a flat Woodland Hills lot typically lands at $220,000 to $280,000 all-in, including the factory-built unit, transport, crane, site work, and finish connection. The catch is customization: you work within the brand’s floor plans and finish packages rather than starting from scratch.

We carry all of those prefab lines, plus Tuff Shed for simpler studio structures and James Hardie for the exterior siding and trim on the site-built projects. That means when we write your price, it reflects the option that actually fits your lot, not just the one we prefer to sell.

What Affects New Detached ADU Pricing in Woodland Hills

• Lot slope and soil. Flat lots south of Ventura Boulevard are the cheapest to build on. Hillside lots above Mulholland Drive frequently need retaining walls, caissons, or both. We see foundation costs double on some hillside parcels compared to a flat lot two miles away.
• Utility trenching distance. The farther your ADU sits from the main electrical panel and sewer line, the more trenching you pay for. A detached ADU at the back of a deep Woodland Hills lot with the panel on the house can add $6,000 to $12,000 in trenching alone.
• Size and bedroom count. A 400 square foot studio runs $220,000 to $250,000. A 900 square foot two-bedroom runs $330,000 to $400,000. The sweet spot for resale value and rental income in this neighborhood is a one-bedroom around 500 to 650 square feet.
• Finish level. Home Depot stock cabinets, laminate counters, and basic LVP flooring keep finishes under $40,000. Custom cabinetry, quartz or stone counters, and engineered hardwood push finishes past $70,000. We write the line items separately on every bid so you see exactly what you’re paying for.
• Access for equipment. Some Woodland Hills backyards are tight. If a mini-excavator or crane can’t reach the build site, crews hand-dig footings and wheel materials in. That labor adds $8,000 to $20,000 depending on the distance and terrain.
• Fire zone requirements. Much of Woodland Hills below Topanga and along the hillsides is in a designated high fire hazard severity zone. That means specific venting, ember-resistant construction, and sometimes a five-foot non-combustible zone around the structure. Those requirements add $5,000 to $15,000 and are non-negotiable at permit review.

How Long Does a New Detached ADU Take in Woodland Hills?

Plan on 12 to 18 months from first design meeting to the day you get keys. That breaks down as roughly 3 to 5 months for design and plan check submittal, 4 to 9 months for Los Angeles Department of Building and Safety review, and 5 to 7 months of actual construction once the permit is issued. Prefab units from Abodu or Cover can shorten construction to 3 to 4 months on site, but the city’s plan check timeline stays the same regardless of how the building is built.

We know that’s a long runway. That’s why we keep a live person on the phone 24/7 during an active build. When you call at 9 p.m. to ask why the surveyor hasn’t shown up, you get an answer, not a voicemail.

How to Save on New Detached ADU

Saving money on a detached ADU in Woodland Hills usually comes down to three moves: keep the footprint modest, choose a prefab plan, and resist change orders once the permit is submitted. Every change after plan check approval costs you both design time and plan check correction fees, which stack up at $200 to $500 per round.

We also recommend building the ADU you’ll actually use. A 400 square foot studio with a proper kitchen and bath rents for $1,800 to $2,200 a month in Woodland Hills and costs $60,000 to $80,000 less to build than a 750 square foot one-bedroom. If the plan is rental income, smaller wins. If it’s an aging parent moving in, spend on the bathroom accessibility and skip the extra square footage.

Material choices are the easiest place to trim without hurting the structure. We’ll always spec the shell, roof, and exterior for longevity in this climate. Where you want to save, you can: laminate counters instead of quartz, stock cabinets instead of custom, a mid-range LVP floor instead of hardwood. Those three changes cut $12,000 to $18,000 from a typical bid. Ask for a line-itemed bid, which is how we write every Seedling price anyway, and you’ll see exactly where the money goes.

For a free written estimate on your specific lot, call (559) 249-3776. We’ll walk the property, measure, and give you a real number rather than a promise.

Prefab vs. Site-Built ADU Costs in Woodland Hills

Here’s the honest comparison, based on the bids we write for both options.

• Site-built 600 sq ft one-bedroom: $260,000 – $320,000. Full design freedom, 5-7 months of on-site construction, higher finish flexibility.
• Abodu 500 sq ft studio: $220,000 – $260,000. Fixed floor plans, 3-4 months on site, faster to permitting because the unit is pre-engineered.
• Cover 600-900 sq ft unit: $240,000 – $300,000. Panelized system, more design flexibility than Abodu, still faster than stick-built.
• Boxabl 400 sq ft Casita: $160,000 – $200,000. Smallest footprint and lowest cost, but limited layout and finish options. Great for a home office or guest space.
• Dvele or Plant Prefab 800-1,200 sq ft: $320,000 – $450,000. Premium prefab, near-custom finish quality, and the highest prefab cost per square foot.

One thing to know about prefab in Woodland Hills: the crane placement matters. If your lot has overhead power lines on the street or a narrow side yard, the crane may need a street closure permit or a longer reach, adding $3,000 to $8,000 to installation. We check that in the first site visit, not when the truck shows up.

Permit Costs and Timeline for Woodland Hills ADUs

Woodland Hills is part of the City of Los Angeles, so ADU permits run through LADBS. Expect $8,000 to $18,000 in total city fees, including building permit, electrical, plumbing, mechanical, sewer connection, and LAUSD school fees (which apply to ADUs under 500 square feet in some cases and are waived entirely past 500 square feet).

Plan check for a detached ADU in Los Angeles currently takes 4 to 9 months, with most of that sitting in the queue. Corrections add two to four weeks per round. We handle every submittal and resubmittal for you, and you’ll know where your permit stands at any point by calling the office.

Why Woodland Hills ADU Prices Differ From the Rest of Los Angeles

Woodland Hills sits in the transition zone between the flat San Fernando Valley and the Santa Monica Mountains. That geography shows up in your bid in two ways: foundation engineering and fire zone compliance. A lot in Northridge or Reseda rarely needs a retaining wall. A lot south of Dumetz Road often does. We bid retaining walls at $300 to $600 per linear foot depending on height, and a 30-foot wall at the back of a hillside lot is a $9,000 to $18,000 line item. That’s the difference between a $280,000 ADU and a $310,000 ADU on the same square footage.

The other local factor is soil. Some Woodland Hills neighborhoods, particularly east of Topanga Canyon Boulevard toward Tarzana, have expansive clay that expands and contracts with moisture. Standard footings in that soil crack over time, so engineers spec deeper footings and more rebar. It’s not a place to save money, and we won’t write a bid that does.

What the Seedling Process Looks Like

Ben Ortega leads our Woodland Hills team, and the process he’s built is designed around one thing: you should know what the project costs before you commit to it, and you should know the house will be cared for while the crew is there.

Here’s what to expect when you call (559) 249-3776:

1. Phone conversation. A live person answers, day or night. We talk about your lot, your goals for the ADU, and whether a site visit makes sense.
2. Free site walk. We measure the yard, check access, locate utilities, and look at slope and drainage. This is where we catch the things that change pricing before they become surprises.
3. Written line-item bid. You get a price in writing that shows every component: design, permits, foundation, structure, systems, finishes, and landscape restoration. No allowance games, no “we’ll figure it out later.”
4. Design and permitting. We handle the architecture, engineering, and LADBS submittals. You approve the design before anything goes to the city.
5. Construction. Background-checked, uniformed technicians do the work. Shoe covers and drop cloths go down every time a crew member steps into your house. Pet-safe products are used where there’s a choice. You get a photo of the clean-up before the crew leaves each day. The promise is called the Cedarwell Care Promise, and it applies to every Seedling project.
6. Completion and walkthrough. We walk the finished ADU with you, check every system, and hand over the keys with the 365-Day Done Right Promise in writing: if it’s not done right, we make it right.

Ben’s team also works with the ADU brands serious homeowners research before calling anyone: Abodu, Cover, Dvele, Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie for exterior materials. If a prefab unit is the right answer for your lot, we’ll tell you. If site-built is better, we’ll tell you that too. The bid reflects what’s right for the property, not what we prefer to sell.

FAQs – New Detached ADU Cost

How much does a new detached ADU cost in Woodland Hills in 2026?

A new detached ADU in Woodland Hills costs $220,000 to $420,000 all-in, with most projects landing between $275,000 and $350,000 for a 600 to 900 square foot unit. Prefab options from Abodu, Cover, or Boxabl start around $180,000 including site work. Call (559) 249-3776 for a written line-item estimate on your specific lot.

What is the cheapest way to build a detached ADU in Woodland Hills?

The cheapest route is a prefab studio under 500 square feet, which runs $160,000 to $240,000 depending on the brand and your site conditions. A Boxabl Casita or Tuff Shed studio on a flat lot with minimal trenching is the lowest-cost path. Keep in mind that permits still cost $8,000 to $18,000 regardless of how cheap the structure is.

Is it cheaper to convert a garage or build a detached ADU in Woodland Hills?

A garage conversion is typically $80,000 to $150,000 cheaper than a detached ADU, landing around $140,000 to $250,000 for a 400 square foot conversion. You save the cost of foundation, framing, and exterior walls. The tradeoff is losing garage storage and a smaller footprint. If the garage is in good condition and you don’t need the parking, converting it is the better value.

How much does a 2-bedroom detached ADU cost in Woodland Hills?

A 2-bedroom detached ADU of 800 to 1,000 square feet costs $330,000 to $420,000 site-built in Woodland Hills. Prefab 2-bedroom units from Cover or Dvele run $280,000 to $400,000 depending on finish level. Add $25,000 to $60,000 on top if your lot is on a hillside with retaining wall needs.

Can a detached ADU be built in the hills of Woodland Hills?

Yes, and it happens regularly. Hillside lots above Mulholland Drive cost $25,000 to $60,000 more than flat lots due to foundation engineering, retaining walls, and sometimes caissons. Fire zone rules add another $5,000 to $15,000 in ember-resistant construction requirements. We walk every hillside lot before quoting so the number reflects the actual site, not an assumption.

How long does it take to build a detached ADU in Woodland Hills?

Total timeline is 12 to 18 months: 3-5 months for design, 4-9 months for city plan check, and 5-7 months of construction. Prefab units cut construction to 3-4 months but don’t change the city’s review timeline. Call (559) 249-3776 and we’ll give you a realistic schedule for your specific project.

Ready to Put a Number on Your ADU?

You don’t have to guess what a detached ADU costs on your Woodland Hills lot. Call (559) 249-3776 and Ben Ortega or a member of his team will walk the property, take real measurements, and hand you a written line-item price before any work starts. No deposits to get a number. No pressure to sign. Just a clear picture of what a new home on your lot will cost, built by a crew that treats your house the way you do.

Pricing reflects the Woodland Hills market as of 2026. Seedling ADU Woodland Hills offers free estimates – call (559) 249-3776.

Written by Ben Ortega, Owner at Seedling ADU Woodland Hills, serving Woodland Hills and the San Fernando Valley.