What's the Cost per Square Foot for an ADU in Los Angeles?
ADUs in Los Angeles in 2026 run $425-$675 per square foot for detached new construction, $350-$525 per square foot for garage conversions, and $525-$800 per square foot for smaller footprints under 500 square feet where fixed costs get spread across less area. A typical 800 sq ft detached ADU lands at $340k-$540k all-in, including design, permits, utilities, and site work under state ADU law.
Why $/sqft Ranges So Widely
The per-square-foot number is misleading if taken as a single figure because fixed costs — utility hookups, permits, kitchen, one bathroom, HVAC — do not scale down proportionally with size. A 400 sq ft studio ADU still needs a full kitchen, bathroom, electrical service, and connection to sewer or a new lateral. Spread across 400 sq ft, those costs push $/sqft into the $600-$700+ range. Spread the same fixed costs across 1,000 sq ft and the number drops to $400-$450. Bigger ADUs cost more in total dollars but less per square foot.
Detached New Construction: $425-$675/sqft
A ground-up detached ADU in LA — new foundation, new framing, new roof, new utility runs — sits at $425-$675 per square foot for a typical build in baseline neighborhoods. West-side premium hoods (Brentwood, Pacific Palisades, Bel Air) push toward the top of the band and beyond. The full stack includes site prep and grading, foundation, framing, roofing, all trades, finishes at mid-to-upper level, appliances, permits, design, and utility work. Hillside parcels under the LADBS Hillside Ordinance add geotech and grading costs that can push $/sqft up another 15-25%.
Garage Conversion: $350-$525/sqft
Converting an existing detached garage to an ADU is the lowest-cost path because the shell already exists. Typical range is $350-$525 per square foot on a 400-500 sq ft footprint. Work includes insulation, drywall, new floor system over slab, kitchen, bath, HVAC, electrical service upgrade, replacement of the garage door with wall and windows, and code-compliant egress. The catch is that older garages often need foundation repairs, new roofing, or complete re-framing once opened up, which can push a garage conversion toward new-construction pricing. One reconciliation, because our own garage-conversion page publishes a market band starting at $75k and the per-square-foot maths above cannot get below roughly $140k. Both are right, and they are not describing the same job. Every figure on this page is for converting a garage into an ADU: an independent dwelling with its own kitchen, bathroom, heating and utility connections. A garage converted into a home office, studio, gym or guest room is not a dwelling, needs none of that, and is what sits at the bottom of the wider band. The moment a kitchen and a separate entrance go in, the project moves into the range on this page and stays there.
Small Footprint Penalty: 500 sq ft and Under
ADUs under 500 sq ft carry the highest $/sqft because the kitchen, bathroom, and utility hookups are essentially fixed costs. Expect $525-$800/sqft for a 300-450 sq ft studio ADU. State law under state ADU law makes ADUs up to 800 sq ft ministerial (no discretionary review), so many homeowners size to 750-800 sq ft to get more livable space for a proportionally smaller cost jump. Going from 500 to 800 sq ft typically adds 30-50% to total cost but 60% more space.
What Is (and Is Not) in the $/sqft Number
A defensible LA ADU $/sqft number includes: design and engineering, LADBS permits and fees, site work and grading, foundation, framing, roofing, all trades roughed and finished, standard cabinets, mid-grade appliances, one bathroom, HVAC, and utility connections within 50 feet of the main house. It does not include: long utility trench runs, sewer capacity upgrades, offsite improvements, solar (the energy code may require it), landscaping, fencing, or driveway work. Ask any contractor quoting $/sqft to itemize what falls outside the number.
Frequently asked follow-ups
Why do some contractors quote $300-$400/sqft when others quote $500-$675? +
The lower quote almost always excludes fixed costs — utility hookups, permits, site work, kitchen, bath — or uses builder-grade finishes that most LA homeowners reject once they see samples. A defensible all-in LA ADU number sits at $425-$675/sqft for detached new construction in 2026. Quotes materially below that band tend to grow via change orders once framing exposes reality.
Is a garage conversion always cheaper than a new detached ADU? +
On paper yes, in practice often no once the garage is opened. Older LA garages frequently need new foundation footings, roof replacement, or complete re-framing to meet current code. When a conversion needs all three, total cost approaches new-construction pricing without the benefit of a purpose-designed layout. A structural walkthrough before committing is worth the small upfront cost.
Does going bigger lower my $/sqft number? +
Yes, up to a point. Fixed costs (kitchen, one bath, utility hookups, permits) spread over more square feet drop the per-foot number. An 800 sq ft ADU almost always beats a 500 sq ft ADU on $/sqft. Beyond 1,000 sq ft the curve flattens and additional space costs closer to marginal framing and finish rates.
Do ADUs need to meet the energy code? +
Yes, every new ADU in California must meet California Energy Commission energy requirements. That covers insulation, windows, HVAC efficiency, lighting, and in many cases solar. Solar can add material cost but is offset over time by lower operating cost, and is often the deciding factor between an $/sqft number that includes or excludes it.
What raises $/sqft the most on an LA ADU? +
Hillside parcels (geotech, grading, retaining walls), long utility runs from the main house, upgraded finishes (natural stone, custom cabinets, imported fixtures), and any structural work required to reinforce the main house foundation or panel to support the ADU. Coastal-zone parcels can add Coastal Commission review, which adds time rather than direct cost but often adds design revisions that do.
Want the same answer applied to your specific project? Onn personally reviews every inquiry.
Written by Onn Cohen-Meguri, founder and designer at Design Onn Point. Onn has spent 20+ years designing and building in Los Angeles. CSLB #1133368.
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