A detached ADU in Los Angeles costs about $300 to $450 per square foot all-in during 2026. A garage conversion runs about $300 to $380 per square foot. The per-foot number falls as the unit gets bigger, because a 400 square foot studio carries the same kitchen, bathroom, permit and utility costs as an 800 square foot one-bedroom.
- Detached ADU
- $300 to $450 / sq ftAll-in, including permits
- Garage conversion
- $300 to $380 / sq ftReuses the structure
- Cheapest per foot
- Bigger unitsFixed costs spread further
- Excluded
- NothingThese numbers include soft costs
What it costs
| What | Typical Los Angeles range | Notes |
|---|---|---|
| 400 to 500 sq ft, detached | $150,000 to $200,000 | $375 to $400 per sq ft |
| 600 to 800 sq ft, detached | $200,000 to $250,000 | $310 to $333 per sq ft |
| 800 to 1,000 sq ft, detached | $250,000 to $300,000 | $300 to $313 per sq ft |
| 1,000 to 1,200 sq ft, detached | $300,000 to $350,000 | $292 to $300 per sq ft |
| Two-storey, up to 1,200 sq ft | $350,000 to $400,000 | $292 to $333 per sq ft |
| Garage conversion, 350 to 400 sq ft | $120,000 to $150,000 | $343 to $375 per sq ft |
Work out your own number. The adu cost calculator gives you a line-item range for your project in under a minute.
Why small units cost more per foot
An ADU has a fixed core regardless of size: one kitchen, one bathroom, one electrical service, one sewer connection, one set of drawings, one permit, one mobilisation of every trade. That core is roughly $90,000 to $120,000 before you have built a single extra square foot of floor.
Spread across 400 square feet, the core alone is $225 to $300 per foot. Spread across 1,000 square feet it is $90 to $120. The extra floor area costs much less per foot than the first 400 did, which is why going bigger almost always improves the per-foot figure and often improves the return.
Be careful which per-foot number you are reading
Most published per-square-foot ADU figures are construction only. They exclude drawings, structural engineering, the energy-code report, city permit and plan check fees, school fees, utility connection fees and site work. Those soft costs run $25,000 to $50,000 on a typical ADU, which on a 600 square foot unit is $40 to $80 per square foot on its own.
Every number on this page is all-in. If a builder quotes you $250 per square foot, ask in writing what is excluded before comparing it to anything here.
What moves the number within a size band
- Site access. If a concrete truck and a lumber delivery cannot get near the build, everything is carried by hand and labour goes up
- Slope and soil. A hillside lot can add $75,000 to $300,000 in foundation work before anything visible gets built
- Distance to the sewer, and whether the main line can take another unit
- Electrical panel capacity, and whether you want a separate meter for the tenant
- Finish level. Rental-grade to upgraded is roughly a 30 percent swing on the interior
- Demolition. Removing an old structure first costs $8,000 to $25,000
The number that matters more than cost per foot
Cost per foot is a comparison tool, not a decision tool. The decision is rent against total cost. A 400 square foot studio at $400 per foot costs $160,000 and might rent for $2,000. A 750 square foot one-bedroom at $320 per foot costs $240,000 and might rent for $2,900.
The bigger unit costs 50 percent more and returns 45 percent more rent, but it also appraises higher and widens your tenant pool. We model both against your actual lot before anyone draws anything.
Los Angeles County figures, reviewed 2026-10-29 by America General Contractors, California contractor licence CSLB 1083262. Planning ranges, not a quote, and not legal advice. We confirm the current rules for your parcel before anything is drawn.
Questions
Is $300 per square foot realistic for an ADU in LA?
At the larger end, yes, all-in. For a 400 square foot unit it is not, because the fixed costs cannot be spread far enough. Treat any quote below $280 per square foot all-in with real suspicion and ask what has been excluded.
Why are prefab ADUs advertised so much cheaper?
Because the advertised price is usually the box, delivered. It commonly excludes the foundation, the crane, site work, utility connections, permits, drawings and finishing on site. Those are the majority of the cost difference, and once they are added the gap narrows sharply.
Does a two-storey ADU cost more per foot?
Slightly, because of the stair, the extra structure and the second-floor framing. But it buys more unit on a small lot, which is often the point.
What is the cheapest legal ADU in Los Angeles?
A junior ADU inside the existing house, at $60,000 to $120,000 for up to 500 square feet. It reuses a bedroom and part of a hallway, so you are mostly paying for a kitchenette, a separate entrance and some electrical.
Related reading
- How much does an ADU cost in Los Angeles?
- What are the ADU setback and height rules in Los Angeles?
- What is a junior ADU (JADU)?
- Garage Conversion Cost in Los Angeles
- Does an ADU Raise Your Property Taxes?
- Pre-Approved ADU Plans in Los Angeles
