If you search for what an ADU costs in Los Angeles, you'll find answers that don't overlap. That's not because someone is lying. It's because "ADU cost" can mean a garage conversion or a new two-story unit, a flat lot or a hillside, and "per square foot" can include or exclude design, permits and utility work.
What published 2026 ranges say
We looked at five Los Angeles builder and consultant pages published in 2026. Treat these as marketing pages, not benchmarks, and note how far apart they are:
| Source | Detached ADU | Garage conversion |
|---|---|---|
| Arc Design Build | $220–$400 per sq ft; 600–800 sq ft typically $175,000–$280,000 | $80,000–$180,000 |
| CCS Inc. | $280–$400 per sq ft | not stated in the excerpt |
| Gaga Construction | $300–$450 per sq ft all-in (custom stick-built $350–$450) | $285–$400 per sq ft |
| NP Line Design | $275–$350 standard, $325–$400 premium | $200–$275 per sq ft |
| MY Cali Builders | $480–$780 per sq ft; $300,000–$540,000 total | $155,000–$265,000 |
Read that table as a warning, not an answer. The highest per-square-foot figure here is nearly four times the lowest, and these pages define "cost" differently or not at all. Anyone who quotes you one clean number before seeing your lot is guessing.
Why the numbers disagree
What's included. Some figures are construction only. Others add design, engineering, permits and fees, and utility connections. Ask any range or quote: does it include architect and structural fees, plan-check and permit fees, school fees, and utility work?
The lot. The same builders point to the same big swings: a sloped or hillside lot adds grading, retaining walls and engineered foundations. Access matters too. A narrow side yard can make deliveries and concrete work harder. Arc Design Build puts sloped lots at roughly 8–18% more and hillside at 20–35% or more; treat those as one builder's opinion.
Detached, attached or conversion. A garage conversion reuses the slab, walls and roof, so it generally costs less per square foot than a new detached unit. It can still need a new foundation edge, insulation, electrical service and a sewer connection.
Utilities. New electrical service, a separate sewer lateral or gas and water lines can be one of the largest "surprise" lines. They depend on what's already at your property.
Finishes. Stock cabinets and LVP flooring versus custom millwork and stone is a bigger lever than most owners expect.
Fees you can check yourself
State law exempts ADUs of 750 square feet or less of interior livable space from impact fees, and school districts can charge fees on ADUs over 500 square feet but not on smaller ones (HCD ADU Handbook). Plan-check and permit fees come from LADBS. Check the current schedule rather than a ballpark; our LA ADU permit guide walks through the steps.
How to get a number you can trust
- Pick a type and a size. Garage conversion, attached or detached, and a target square footage.
- Write a scope with inclusions and exclusions. See our guide to writing a scope that gets comparable bids.
- Get at least three bids on the same scope. The California Contractors State License Board recommends three (CSLB). Our step-by-step on getting three bids covers how.
- Ask what's excluded. Scaffolding, permits, utility upgrades and landscaping are the usual gaps.
- Keep a contingency. Ask your contractor what they'd set aside for unknowns on your specific lot.
If you'd rather compare bids side by side, you can post your ADU project on Bidroom for free and see what licensed contractors send back. If you're deciding between a conversion and a new build, start with our garage conversion guide.
Prices change quickly. This page was last reviewed in October 2026.
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