How Much Does an ADU Cost in Los Angeles? (2026 Breakdown)

What an ADU actually costs in LA.

If you've been quoted scary six-figure numbers, you're not wrong — but the picture is more nuanced than the sticker shock suggests.

Reframe the sticker shock: the statewide median ADU cost is about $150,000 (~$250/sq ft), and 71% of California ADUs cost under $200,000, per the UC Berkeley Terner Center owner survey. The LA premium ($300–$450/sq ft) is real — but most ADUs are not the $650k horror stories you read about. Smart scoping, the right ADU type, and a builder who knows local LADBS rules keep you on the right side of that median.

Cost breakdown by build type.

The single biggest lever on your final number is which type of ADU you build. Here's how the four main paths compare in Los Angeles.

Garage Conversion

The cheapest route to a legal ADU — you reuse the existing slab, walls, and roof, so you're paying mostly for systems and finishes, not structure.

• Lowest cost per square foot of any type
• Fastest timeline (clean conversions finish in 4–6 months total)
• Watch for: electrical panel upgrades, sewer tie-in, and bringing an old slab up to code

Prefab / Modular

Built in a factory and craned onto your lot. Often 10–20% cheaper on straightforward jobs — but the headline "base price" is not the final price. See our full prefab vs. custom ADU cost breakdown.

• Faster on-site install (weeks, not months)
• Base price ≠ final price: site work, utilities, foundation, and permit fees are usually add-ons (often $40k–$60k extra)
• NOT "done in a month" — permitting, sitework, and factory queues still apply

Custom Stick-Built (Detached)

A fully custom unit built on-site. Maximum design flexibility — and the type most likely to see cost overruns if scoped loosely.

• Total control over layout, finishes, and size
• Highest cost and longest timeline of the four
• Best paired with a fixed-price contract to avoid change-order creep

Attached ADU

Added onto your existing home, sharing a wall. Often less expensive than a standalone detached unit because it can share structure and some utility runs.

• Can reuse part of the existing foundation and utility connections
• Good middle-ground on cost between conversion and detached
• Layout is constrained by your home's existing footprint

The full all-in cost stack.

"Cost to build" is only part of the story. Here's the complete picture for a typical LA detached ADU, so nothing surprises you later.

• Cost Bucket: Hard construction — What it covers: Foundation, framing, roof, MEP, finishes — the build itself — Typical range (LA): $300–$450 / sq ft
• Cost Bucket: Design & engineering — What it covers: Plans, structural engineering, Title 24 energy, surveys — Typical range (LA): $8k–$25k
• Cost Bucket: Permits & city fees — What it covers: LADBS plan check + permit fees (impact fees waived under 750 sq ft) — Typical range (LA): $3k–$15k
• Cost Bucket: Utilities & site work — What it covers: Separate meter, sewer lateral/pump, grading, access — the #1 under-budgeted item — Typical range (LA): 10–15% of total
• Cost Bucket: Solar (if required) — What it covers: New-construction detached ADUs typically require solar under Title 24 — Typical range (LA): $8k–$15k

The 750-sq-ft sweet spot: impact-fee exemption

Under California state law (SB 13), ADUs under 750 square feet are exempt from local development impact fees. On many LA projects that's thousands of dollars erased from the budget — which is exactly why so many ADUs land right around that size. A builder who knows the rule can scope your unit to capture the exemption.

Three things competitors won't tell you.

The "$40,000 CalHFA grant" is currently paused

The CalHFA $40,000 ADU Grant covered pre-development costs — but the last round was fully allocated in December 2023 and the program is currently paused and out of funds, with no confirmed relaunch. Many builder pages still advertise it as live. It may reopen if the state appropriates new money, so check the official CalHFA ADU page before counting on it. (See our ADU financing guide for the paths that actually work today.)

The "60-day permit" is the law, not your real timeline

California statute requires the city to approve or deny a complete ADU application within 60 days. In practice, that clock is widely missed on custom builds — a real LA custom permit takes 3–6 months, with the correction-loop being the painful part. Pre-approved LADBS Standard Plans are the genuine fast track (often 21–30 days). Treat any builder who "guarantees a 60-day permit" with caution.

A contractor cannot legally take a big deposit up front

California law (BPC §7159.5) caps a contractor's down payment at $1,000 or 10% of the contract price, whichever is less — which means effectively $1,000 on any ADU. "Material reservation," "lumber-lock," or "pre-construction onboarding" fees that ask for tens of thousands up front are repackaged illegal deposits. Every builder in our directory is verified to operate within this cap and carries an active CSLB license you can look up yourself.