What Is the Cost of an Accessory Dwelling Unit in San Diego?

Many local and site-specific factors determine the cost of building an ADU in San Diego, including access to the backyard, topography, utility location, sewer or septic, school fees, permits, etc. USModular's starting cost for a 398 square foot, one bedroom ADU (Federal Building Code) is $78,000, which includes the ADU, transportation to the site, roll set/installation on a permanent foundation, and connection to utilities. Local fees generally range from 5-15% of the construction cost. Financing options are available.

Why Hire US Modular San Diego ADU Builders?

US Modular San Diego ADU builders offer construction that is better, faster, greener, and more cost-effective due to our prefabricated site construction approach. Unlike site-built projects that require months of construction, our prefabricated ADUs are set in your backyard in a single day, minimizing disruption. A small crew then completes finish work and utility connections.

Your ADU Contractor in Los Angeles

Q: How Many ADUs Can I Build?

On a residential lot, you may build one detached ADU and one junior ADU (up to 500 square feet and located within the home). On a multi-family lot, up to two detached ADUs are permitted.

Create More Space—or a New Income Stream—Without the Headaches

USModular Home Builders is the Accessory Dwelling Unit (ADU) contractor Los Angeles homeowners trust for turnkey backyard units that go up fast and look fantastic. We make adding a backyard cottage, granny flat, or rental unit remarkably simple. Our team brings 75+ years of combined experience in general contracting and real estate development to every Los Angeles ADU project, so you get expert guidance from the first site visit to final inspection.

Your brand-new unit is craned into place and weather-tight in a single day, minimizing disruption to the main house and the neighborhood. Curious about what a prefab ADU in Los Angeles costs or how ADUs compare to stick-built? We’ll walk you through every option and line item before we break ground.

Discover just how fast and stress-free a Los Angeles prefab ADU can be.

LET’S BUILD IT

Advantages of Adding an Accessory Dwelling Unit (ADU) in Los Angeles

An ADU is a secondary home built on the same lot as your primary residence. Thanks to updated California regulations, an ADU can be as large as 1,200 sq ft. Thousands of Los Angeles ADU projects are popping up because they slot new housing into existing neighborhoods with very little disruption. Here’s why an ADU Los Angeles prefab build might be a smart move for you:

More Affordable Housing: ADU construction typically costs less than buying or building a separate home, and you’re leveraging land you already own.
Multigenerational Living Made Easy: From aging parents to recent grads, an ADU prefab in Los Angeles lets families stay close while each generation maintains their privacy.
Built-In Rental Income: With LA’s steep home prices, many owners build ADUs to create a steady rental stream that helps offset the mortgage.
Minimalist & Sustainable: Smaller footprints, lower utility bills, less stuff. An ADU supports the growing movement toward simple, eco-friendly living—all within your favorite neighborhood.
Boosted Property Value: Buyers love flexibility. Appraisers now give solid credit for well-designed backyard units, so you can recoup your ADU’s cost with a higher resale value.
Wide Range of Styles & Sizes: Need a sleek studio or a single-family dwelling with up to four bedrooms? Our catalog covers it. Visit our sister site for all the available home models for your lot.
Versatility in Placement:
- Detached, stand-alone cottage
- Attached addition to the main house
- Junior ADU converted from existing space inside the home

Get inspired! Check out our Project Gallery featuring some of our newest ADUs.

How a Prefab ADU in Los Angeles Is Made

“Prefab” simply means “previously fabricated.” Your Los Angeles prefab ADU is constructed inside a climate-controlled factory, shipped in modules, then craned onto a permanent foundation and buttoned up on site—often within 24 hours. Because most of the work happens indoors, ADU construction timelines shrink dramatically, weather delays disappear, and quality control soars. USModular follows four clear phases to keep every project on budget and on schedule:

Phase 1 – Planning

Site visit to verify setbacks, utility locations, accessibility, and floor-area-ratio (FAR) rules unique to Los Angeles ADU codes.
Confirm ADU submittal requirements for city or county review.
Decide whether your unit is Modular (CBC/local) or Manufactured (HUD/federal).
Develop a transparent conceptual budget, including the cost for the unit and all site work.

Phase 2 – Construction Contract

Lock in the final budget and sign a fixed-price contract so there are no surprises.

Phase 3 – Plan Design & Submittal

Draft a detailed site plan.
Secure state-approved third-party and City of LA approvals.
Fabricate the ADU in the factory while our field crew preps the foundation, utilities, and any required upgrades.
Coordinate inspections with Los Angeles building officials—your USModular project manager handles every call and checklist.

Phase 4 – Final Inspection & Handover

USModular walks through the finished unit with you, addresses any punch-list items, and obtains the Certificate of Occupancy.
We hand you the keys to a move-in-ready ADU

2025 Rules & Perks for Building an Accessory Dwelling Unit in Los Angeles

Recent state and city updates make Los Angeles ADU construction projects even easier. Here are the rules every homeowner, investor, and ADU contractor in Los Angeles should know. You can get detailed information on our City of Los Angeles ADU Rules & Regulations page.

Size Flexibility: Detached or attached ADUs may be built up to 1,200 sq ft—regardless of the main home’s size—as long as setbacks and floor-area-ratio limits are met. A junior ADU inside the primary home can be up to 500 sq ft.
Streamlined Setbacks: Side- and rear-yard setbacks are just 4 ft, opening up far more backyards for a Los Angeles prefab ADU.
Parking Relief: No on-site parking is required if your lot is within 1/2 mile of public transit (most of LA). Even when parking is required, converting an existing garage meets the rule.
No Owner-Occupancy Requirement: Through at least 2025, the state waives owner-occupancy, meaning investors can rent out both the main home and the new unit.
60-Day “Shot Clock”: Local building departments must approve or deny a complete ADU Los Angeles permit application within 60 days—or it’s deemed approved.
Impact-Fee Waiver: City and county development fees are waived for any prefab ADU Los Angeles cost that lands under 750 sq ft, shaving thousands off the budget.
Multifamily Bonuses: Duplexes, triplexes, and larger buildings can add at least one detached ADU, plus up to 25 % of the existing unit count as internal conversions.
Fire-Sprinkler Clarity: Sprinklers are only mandatory in your ADU if the primary dwelling already has them.

Frequently Asked Questions: ADU Contractor, Los Angeles

Below are a few of the questions we hear most often as ADU contractors in Los Angeles. Have something else on your mind? Reach out—our team is happy to walk you through your goals.

What is the cost of an accessory dwelling unit in Los Angeles?

Because every backyard is different, the cost depends on access, slope, utility tie-ins, school fees, and local permit charges. For reference, our 398-sq-ft, one-bedroom Los Angeles prefab ADU (built to HUD code) starts at around $78,000. That includes the unit itself, factory transport, crane set on a permanent foundation, and basic utility connections. City or county fees typically add 5–15 percent. If you need financing, we partner with lenders who understand ADU construction Los Angeles-style and can bundle site work and unit costs into one loan.

Why hire USModular as my ADU builder in Los Angeles?

Speed, certainty, and far less chaos. Traditional stick builds mean months of hammering, dumpsters, and a dozen tradespeople in your yard daily. With our approach, the unit is 90 percent finished in the factory. We crane it into place in one day, then a small crew spends a few weeks on utility hookups and final touches. In short: better quality control, faster move-in, greener construction, and often lower total cost. That’s why so many owners choose USModular as their ADU contractor.

How many ADUs can I build on my property?

On a standard single-family lot in LA, you’re allowed one detached ADU up to 1,200 sq ft plus one junior ADU of 500 sq ft or less inside the primary home. Own a multifamily property? Regulations let you add at least one—and sometimes two—detached units, plus convert up to 25 percent of existing interior space into additional apartments. Our team of ADU building experts will confirm exactly what your zoning allows and design a plan that maximizes your lot’s potential.

Build a Dream With USModular—Your ADU Contractor in Los Angeles

USModular turns backyard blueprints into beautifully finished living spaces that fit LA’s vibe and your budget. Whether you imagine a chic rental, a comfortable in-law suite, or a sleek studio to work from home, our ADU builders in Los Angeles guide you from first sketch to final key hand-off—fast, simple, and transparent. Let’s create the Los Angeles ADU that matches your lifestyle, boosts your property value, and starts earning income sooner than you thought possible. Questions? Call (888) 987-6638.

Build Your Prefab Home Now! Questions? Call (888) 987-6638