A detached ADU in Los Angeles costs $150,000 to $400,000-plus, which works out to roughly $350 to $500 per square foot for standard construction and $500 to $650 for high-end finishes in places like Brentwood or the Palisades. A garage conversion is cheaper, usually $80,000 to $180,000, because the slab and shell already exist. The spread is wide because square footage is only one input. Site access, sewer distance, panel capacity and hillside status often matter more than the floor plan. Below is how the cost actually stacks up at four common sizes.
What each size actually costs in 2026
Smaller units cost more per square foot because the expensive parts — kitchen, bathroom, electrical service, foundation setup, utility trenching — do not shrink with the floor plan.
- **400 sq ft studio:** $170,000 to $230,000. That is $425 to $575/sq ft. One bathroom, kitchenette, no interior walls to speak of. - **600 sq ft one-bedroom:** $220,000 to $300,000. Around $365 to $500/sq ft. The most common size we build in the Valley. - **800 sq ft two-bedroom:** $280,000 to $380,000. Roughly $350 to $475/sq ft. Second bathroom typically adds $18,000 to $28,000. - **1,200 sq ft (the state cap for a detached ADU on most lots):** $390,000 to $560,000. Economies of scale flatten out and finish level dominates.
These numbers assume a flat lot, a driveway a truck can back down and a sewer lateral within about 60 feet.
Pro Tip
If you are choosing between 550 and 600 sq ft, build the 600. The marginal cost of the last 50 feet is framing and flooring, not systems.
The hard cost line items on a 600 sq ft build
Here is roughly how $260,000 distributes on a mid-range 600 sq ft detached unit in Los Angeles:
- Site prep, grading, demo: $8,000 to $16,000 - Foundation (conventional slab on grade): $18,000 to $28,000 - Framing, sheathing, structural hardware: $34,000 to $46,000 - Roofing and exterior weatherproofing: $12,000 to $20,000 - Windows and exterior doors: $9,000 to $18,000 - Rough plumbing including sewer tie-in: $14,000 to $26,000 - Electrical rough and new subpanel: $11,000 to $19,000 - HVAC, typically a ductless mini-split heat pump: $7,000 to $12,000 - Insulation and drywall: $10,000 to $16,000 - Kitchen cabinets, counters, appliances: $16,000 to $38,000 - Bathroom complete: $12,000 to $22,000 - Flooring, interior doors, trim, paint: $14,000 to $24,000 - Exterior stucco or siding: $12,000 to $22,000
Swapping quartz for slab marble and stock cabinets for custom can add $25,000 on its own.
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Soft costs people forget to budget
Soft costs typically land at 10 to 18 percent of the project and they are due before a single shovel moves.
- Architectural plans and Title 24 energy compliance documentation: $8,000 to $22,000 depending on complexity - Structural engineering: $2,500 to $7,000, higher on sloped sites - Soils report, required on many hillside and expansive-soil lots: $2,500 to $6,000 - Survey: $1,500 to $4,500 - City plan check and permit fees: commonly $4,000 to $12,000 for an ADU in the City of LA - School fees: assessed per square foot of new habitable area
Under the LA ADU ordinance (Ordinance 186,481, codified at LAMC 12.22A.33) and state law, ADUs under 750 sq ft are exempt from impact fees, and utility connection fees for units built within or attached to an existing structure are limited. That exemption is a real reason a lot of Valley owners stop at 749 sq ft.
Pro Tip
Ask for a fee estimate at the schematic stage, not after plan check. It sometimes changes the design.
Site conditions that swing the price $40,000
Two identical 600 sq ft units, one in Sherman Oaks flats and one off Mulholland, can differ by $80,000 for reasons that never appear on the floor plan.
**Hillside.** If the lot falls under the Baseline Hillside Ordinance (Ordinance 184,802), expect caissons or a stepped foundation instead of a slab. That alone runs $35,000 to $90,000. Add haul-off costs for export soil and restricted street access.
**Electrical service.** Many older Highland Park, Culver City and Van Nuys homes still run a 100-amp main. An ADU with a heat pump, induction range and an EV charger will not fit. A service upgrade to 200 amps is $4,500 to $9,000, more if LADWP needs to reset the pole or the run is underground.
**Sewer.** If the lateral is far from the unit or runs uphill, you need a longer trench or an ejector pump. Budget $8,000 to $25,000.
**Fire access and sprinklers.** If the main house has fire sprinklers, the ADU generally needs them too. That is $8 to $14 per sq ft.
Setting a budget you can actually build to
Work backwards from a total, not up from a wish list. Take your all-in number, hold back 12 to 15 percent as contingency, subtract 15 percent for soft costs, and what remains is your construction budget. On a $300,000 all-in ADU that leaves about $215,000 of hard cost, which lands you a well-built 550 to 650 sq ft unit with good but not exotic finishes.
Get the site investigated before you commit. A $3,000 soils report and a panel check at the start prevents the $50,000 surprise at month three. We price ADUs after a site walk for exactly this reason — sewer depth, slope, service size and access tell us more about the final number than the square footage does.
Construction on a detached unit typically runs 5 to 8 months from permit issuance to final inspection, with design and plan check preceding that.
Pro Tip
Order the soils report and a sewer camera inspection before you approve final plans. Both are cheap relative to what they can reveal.
Final Thoughts
ADU pricing in Los Angeles is driven less by size than by site. A flat lot in Northridge with a 200-amp panel and a close sewer lateral is a very different job from a Baseline Hillside parcel with a 100-amp service. Budget $350 to $500 per square foot for standard construction, hold real contingency, and spend money on site investigation before design. That order of operations is what keeps the final number close to the first one.
Frequently Asked Questions
Budget $220,000 to $300,000 all-in for a 600 sq ft detached ADU in Los Angeles, or roughly $365 to $500 per square foot. That includes design, engineering, permit fees and construction. Hillside sites, a 100-amp electrical service or a distant sewer lateral can push the top of that range considerably higher.
Yes, usually by a wide margin. A garage conversion in Southern California typically runs $80,000 to $180,000 because the slab, walls and roof already exist. You are paying for insulation, a new floor assembly, plumbing, electrical, windows, a kitchen and a bathroom rather than a full structure.
Because the expensive components do not shrink. A 400 sq ft studio still needs a full bathroom, a kitchen, a subpanel, a sewer connection, a foundation and a roof. Those fixed costs spread over fewer square feet, so a 400 sq ft unit can run $425 to $575 per square foot while a 1,200 sq ft unit lands nearer $350.
ADUs under 750 square feet are exempt from development impact fees under state law, and utility connection charges are limited for units created within an existing structure. This is why many Los Angeles owners deliberately design to 749 square feet. Plan check and permit fees still apply, commonly $4,000 to $12,000.
Construction on a detached ADU typically runs 5 to 8 months from permit issuance to final inspection. Design, engineering and plan check happen before that. Garage conversions are usually shorter because there is no foundation or framing package, though utility and structural upgrades can extend the schedule.
