Is a Prefab ADU Cheaper Than a Custom ADU in Los Angeles?

By Babak Mortazavi January 22, 2026

Quick fact: across LA, many prefab ADUs come in 10%–20% cheaper than traditional construction for the same size and finish, thanks to factory-built efficiency. The full picture, however, still depends on site preparation, utility connections, permits, and upgrades.

This guide explains how prefab ADU prices really work in Los Angeles, how they compare with traditional builds and garage conversions, and how LADU's architect-led team keeps your accessory dwelling unit on budget.

You'll learn:

Prefab ADU cost and unit pricing vs. total project costs for traditional construction in LA, with real ranges by size.
Every line item that affects the overall cost and how economies of scale lower per-square-foot pricing.
How prefab units built in a factory can shorten your ADU project and what that means for construction costs.
When a prefab ADU home is the right fit vs. a custom ADU, plus zoning basics and ADU plans that move through review faster.
How LADU streamlines design, ADU building permits, and build with fixed pricing. No Surprises, along with financing options and next steps to prefab ADU success.

By the end, you will know when a prefab ADU is cheaper than traditional builds on your lot, how to evaluate quotes from prefab ADU builders and prefab ADU companies, and how to avoid hidden costs.

At LADU, we make adding a prefab ADU to your property simple. We'll help you find the perfect ADU design that fits your space and allows you to meet your goals. Schedule your free site visit today, or call (213) 855-3334 to learn more.

ADUs Designed Better. Built Smarter.

Is a Prefab ADU Cheaper in Los Angeles?

The short answer is yes, a prefab ADU is cheaper based on the unit itself for many projects. Prefab ADUs are often 10%–20% cheaper than traditional construction on a per-square-foot basis.

A common range for a prefab ADU runs $150–$300 per square foot, whereas site-built or custom ADUs often fall between $250 and $400+ per sq. ft.

Total pricing depends on the full scope, including foundation, delivery, installation, utility connections, and permit fees through the City of Los Angeles or your local jurisdiction.

ADU Prefab Cost Ranges for LA Homeowners

Here are realistic price ranges many LA homeowners see when comparing prefab ADU cost against site-built options. These prices reflect typical factory specs with standard finishes. Upgrades, longer utility runs, or difficult access can move a quote higher.

400–500 sq. ft. studio or compact one-bedroom ADU: $80,000–$150,000 for a prefab unit, plus delivery, installation, utilities, and permits. Total project costs can land above that unit price depending on site conditions.
500–800 sq. ft. one-bedroom or large one-bedroom ADU with den: $150,000–$300,000 for the prefab unit, with strong value on simple footprints.
800–1,200 sq. ft. two-bedroom or two-bath ADU layouts: $250,000–$450,000 for the prefab unit, with better per sq. ft. math at the larger end due to economies of scale.
Garage conversion ADU: $100,000–$180,000 total is common in LA when the garage structure is viable and existing utilities are nearby, which can be the lowest total cost path on many lots.

Bigger footprints often lower per-square-foot costs on the unit. The percentage savings can narrow once cranes, access work, or extensive trenching come into play.

When Prefab ADU Cost Rises

There are cases where the overall cost for a prefab ADU home and the price to build an ADU end up being close. This often happens when:

Crane access is complex or requires street closures and traffic control.
Power, water, sewer, or gas lines sit far from the ADU location, driving trenching and paving repair costs.
Backyard access needs widening or removals of fences and trees.
Finishes, appliance packages, and window upgrades push the prefab spec toward custom-level selections.

Watch for hidden costs in any quote. Some advertised prefab ADU prices exclude delivery, foundation, set day crew, utility connections, permit intake, and local plan sets. Ask for each line item in writing so you can compare apples to apples.

Full Prefab ADU Cost Breakdown

Here is a line-by-line list you can use to build a complete prefab ADU cost comparison across vendors and scopes.

ADU Prefab Homes Pricing and Finishes

The factory price covers the building shell and interior finishes delivered complete or in modules. Standard specs often include cabinets, counters, plumbing fixtures, windows, doors, insulation, drywall, flooring, lighting, and a mini-split or similar HVAC.

Many prefab ADU companies offer upgrade menus for appliance brands, window packages, siding, roof profiles, tile, and hardware. These selections shift the price and can affect lead times.

Clarify what the base unit includes, and request a list of upgrades with costs. Ask if design fees apply for plan revisions, local site sheets, or Title 24 energy documentation.

Some vendors include a standard plan set for state approval and then charge for Los Angeles-specific sheets, fire notes, or revisions for your lot.

Site Preparation and Foundation

Most prefab ADUs need a slab, stem wall, or pier foundation. Scope can include grading, excavation, trenching for utilities, and compaction. Access planning for cranes or roll-in delivery often starts here, since paths, turning radii, and overhead lines affect layout.

Typical site preparation in LA ranges from $10,000–$40,000 based on slope, soil, and distance to utilities.

Delivery, Installation, and Craning

Delivery covers transport from the factory to your street, plus staging and the set day crew to place the unit.

Craning costs vary with tonnage, reach, and site constraints. Narrow streets, steep drives, and overhead power can push costs up, since a larger crane or more traffic control may be required.

Delivery and installation can run five figures on many LA projects, and it is worth confirming if escort cars, street permits, or police details are included.

Utilities, Permits, and Impact Fees

Utility connections cover new or upgraded electric service, sub-panel runs, water line and meter sizing, sewer or septic tie-ins, and gas lines if the model is not all electric. Panel upgrades are common when the main house has limited capacity.

Permitting includes application intake, plan review, corrections, and inspections. In Los Angeles, permit costs and plan check fees often land in the low thousands for smaller units, with school impact fees applying for ADUs 750 sq. ft. and larger.

Development impact fees are waived up to 750 sq. ft. under state rules, and some agencies assess fees for larger units.

LADU's ADU Building Permit Services handle all permitting requirements for you, and we explain all utility and impact fees upfront so there are no surprises down the road.

Checklist To Get an Accurate Prefab ADU Price

Use this list with any vendor to capture the complete scope for installing a prefab ADU in Los Angeles.

Scope Line Items To Request

Unit spec sheet with make, model, dimensions, insulation, window package, HVAC, and finish schedule.
Foundation type and thickness with engineering, anchor details, and termite barrier.
Delivery and crane plan, route survey, and traffic control if needed.
Installation and set day crew, including weather contingency.
Utility connections for power, water, sewer, gas, and panel upgrade if required.
Permit handling, plan submittal, corrections, and inspection coordination.
Finals, punch list, and warranty handoff.

Site Prep and Utility Allowances

Ask for clear dollar allowances for grading, trenching, compaction, electrical upgrades, sewer tie-in, water meter work, and paving repair. Pricing clarity reduces change orders and keeps your budget predictable.

Delivery, Access, and Schedule

Confirm the delivery route, staging area on site or on the street, set date window, and contingency days. Get the crane size and reach in writing with any required permits.

Sample Line Items

Prefab unit, Model X, 620 sq. ft. – $____ per unit
Foundation, slab on grade, 620 sq ft – $____ per sq. ft.
Crane, 200-ton, 6-hour set – $____ lump sum
Electrical, 125A sub-panel, 120-ft. trench – $____ per linear foot
Sewer, 6-inch tie-in, 80-ft. trench – $____ per linear foot
Permits and plan check – $____ allowance
Paving repair, 200 sq. ft. – $____ per sq. ft.

Prefab ADU vs. Traditional Construction

Prefab ADUs and traditional builds achieve the same goal with different processes. Here is how those differences show up in time, labor, disruption, and quality.

Timeline and Labor Costs

Prefab units are built in a factory at the same time the foundation and utilities are built on site. This parallel path shortens the calendar and reduces labor costs in your backyard.

Typical prefab timelines run 2–6 months from order to final inspection, depending on lead times and permit windows. Traditional construction often runs 6–9+ months since every trade builds on the last trade in sequence.

Disruption and Schedule Risk

Factory production avoids weather for much of the build and reduces days with large crews at your home. You still have trenching and foundation work on site, but that period is shorter with prefab units, which reduces the impact on daily life.

Plan for manufacturing lead times and inspection windows, since those items set the project rhythm.

Quality Control With Factory Builds

Units built in a factory benefit from repeatable processes and tight tolerances. Jigs, controlled environments, and consistent crews lead to stable quality. With a clear scope and fixed specs, homeowners also see fewer change orders, which improves price predictability.

Size, Layout, and Economies of Scale Impact Prefab ADU Prices

Size and layout drive pricing for prefab ADU homes. Larger footprints spread fixed costs across more square feet, which can lower the per-square-foot number.

Studio ADU Around 400 Square Feet

Studio ADUs pack a sleeping area, kitchenette, and bath into a compact footprint. Typical prefab ADU prices for a studio fall near $80,000–$150,000 for the unit, with range driven by window packages, cabinetry, and tile selections.

A simple finish package keeps totals down. Premium tile, wide glazing, and built-ins push totals up.

One-Bedroom ADU 500–800 Square Feet

One-bedroom layouts add a full kitchen, defined living space, and storage. Many families include laundry rooms. Price bands for the unit often land at $150,000–$300,000.

Price per square foot can drop as you move from 500 to 800 sq. ft., since framing, shipping, and setup include fixed costs that do not scale one to one with size.

Two-Bedroom ADU 800–1,200 Square Feet and Two-Story Options

Two-bedroom layouts bring higher totals but better per-square-foot economics. Stairs, structural requirements, and added baths increase cost.

Two-story options often track closer to a custom build since structural and craning needs increase and city review can be more involved for height and fire access.

Site Conditions That Change Prefab ADU Pricing in LA

Flag these cost drivers early. A short site walk with an expert can save weeks and protect your budget.

Sloped or Narrow Lots and Crane Access

Slope can trigger retaining needs or more excavation. Narrow lots, tight alleys, and overhead lines affect crane selection, street permits, and set day timing. This is one of the fastest ways for construction costs to climb if missed in the estimate.

Utility Connections Distance and Upgrades

Long sewer runs across the yard, undersized water meters, or main panel upgrades can add work. If the ADU is far from the utility tie-ins, count on more trenching and paving repair. All-electric models may also need higher service capacity to run HVAC and appliances.

Soils, Drainage, and Driveway Access

Soft soils, high groundwater, or poor drainage can require thicker footings, subdrains, or soil remediation. Delivery paths sometimes need driveway widening or temporary removals of gates or trees.

Permits, Zoning, and Prefab Approvals in Los Angeles

Prefab units still pass through local review for the site. LADU's team coordinates the submittal and tracks comments with your plan checker.

Size Limits, Setbacks, Height, and Fire Access

Los Angeles follows state ADU size rules that allow detached units up to 1,200 sq. ft. in most residential zones. Standard setbacks are small for ADUs, and height limits apply.

Fire department access, street width, gates, and hydrant spacing can affect placement, and hillside areas may have added rules.

Plan Review for Prefab Units and Local Compliance

Many prefab ADUs use state or third-party approvals for the building itself. The city still reviews your site plan, foundation, utility sheets, grading, and any local notes for fire and energy.

LADU prepares the full package, responds to corrections, and coordinates the installer so the site plan and the factory plan align.

Fees, Impact Charges, and Grants

Expect plan check and permit fees, plus school impact fees for units 750 sq. ft. and larger. Local development impact fees are waived for ADUs up to 750 sq ft under state law.

Some homeowners qualify for the California ADU Grant Program that can offer up to $40,000 toward soft costs.

Financing and ROI for Prefab ADU Homes

A clear plan for funding and payback turns a quote into a project. LADU helps you run the numbers so your ADU supports your long-term goals.

Financing Options for LA Homeowners

Popular options include HELOCs, cash-out refinance, and construction loans. LADU can connect you with financing options that fit your timeline and credit profile.

Rental Income Ranges and Payback Math

Detached prefab ADU homes in LA often rent in the following ranges, with variation by neighborhood and finish level:

Studio: Roughly $1,900–$2,600 per month
One-bedroom: Roughly $2,300–$3,200 per month
Two-bedroom: Roughly $3,000–$4,200 per month

Simple payback sketch: a $220,000 project financed at a blended monthly cost of $1,600–$1,900 including mortgage, insurance, and maintenance can pencil with a one-bedroom that rents near $2,600–$3,000 per month.

Vacancy, management, and reserves should be included in your model.

When a Custom ADU or Garage Conversion Is a Better Choice

Prefab is not the best fit on every lot. Reusing a sound garage structure can reduce foundation work and shorten utility runs, which lowers totals more than a detached prefab unit in many cases.

Tricky access, strict HOA rules, or a tailored layout can also point to a custom ADU. A custom build can shape the plan to match heritage trees, privacy needs, or a second story that aligns with views and setbacks.

How LADU Streamlines Prefab ADUs in LA

LADU is built for Los Angeles ADUs. Our architect-led ADU Design Services map zoning, utilities, and access on day one, and then we permit your project in house and arrange construction through vetted, licensed prefab ADU builders.

Fixed Pricing. No Surprises.

Flat-fee design packages, clear allowances, and guaranteed construction pricing protect you from scope creep and surprise change orders. You see the numbers up front and keep them stable.

Ready To Begin Your ADU Project?

Ready to discover your property's true potential and map your next steps with a local expert? Schedule your free site evaluation today, or call (213) 855-3334 to connect with our team to discuss prefab ADU design options, permitting timelines, and site preparations.

Design + Permitting + Build = LADU.