How much an ADU costs in Los Angeles in 2026

What the independent data says

The only independent, statewide look at what owners actually paid is the Terner Center's ADU owner survey, released April 22, 2021. It found a median construction cost of $150,000, about $250 per square foot. Thirty-seven percent of the new ADUs in the survey cost less than $100,000 and 71 percent cost less than $200,000.

Those figures are five years old, statewide and self-reported. Labor and materials have risen since, and Los Angeles sits at the expensive end of the state: hillside properties, very high fire hazard zones and older houses with small electrical services all add work. Treat the survey as a floor for planning, not a quote.

Most 2026 price lists you will find online come from builders and plan sellers. They are useful for a sense of range, but each one is also a sales page. The reliable number is a bid on your property, which is why the last section of this guide is about getting one.

The three kinds of ADU and what moves the price

Garage conversion. You keep the walls, roof and, in most cases, the slab. LADBS's conversion bulletin allows an existing slab to stay with an approved sealant as a moisture barrier, and existing footings to stay if they are free of excessive cracking and meet the minimum dimensions. What you pay for is the infill wall where the garage door was, insulation and energy work, a bathroom, a kitchen, a separate electrical panel and finishes. See the guide on converting a garage into an ADU.

Attached ADU. An addition on the existing home, up to half the home's floor area or 1,200 sq ft, whichever is less. It shares a wall and often a roofline, which saves exterior work, but it needs its own foundation and ties into the existing structure.

Detached ADU. A new building, up to 1,200 sq ft. Everything is new: foundation, framing, roof, utilities trenched from the street or the house. The size you choose matters more than anything else, and a pre-approved plan can take design cost off the table.

Four site conditions move any of these up:

• A very high fire hazard zone or a hillside street, where LA City has extra rules for detached ADUs and may require fire sprinklers.
• A fire hydrant more than 150 ft from any part of the ADU along the access path, which LAFD can answer with a sprinkler requirement.
• Soil that needs site-specific foundation work. LADBS notes that localized soil conditions may require it even with a standard plan.
• An electrical service that cannot carry a second home. The LADBS bulletin requires a separate electrical panel for the ADU.

What the city charges

City and school fees are a small share of the total, and the 2026 state law cut them further. The rules below are from the ADU rules file the property report is built from, with its sources.

Fee	Rule since January 1, 2026
Development impact fees	None on an ADU of 750 sq ft or less, or a junior ADU of 500 sq ft or less, measured as interior livable space. Above that, charged in proportion to the main home's size.
School fees	None on an ADU or junior ADU of 500 sq ft or less. Above 500 sq ft, LAUSD's residential rate is $5.17 per sq ft (adopted June 2024, adjusted every two years).
Utility connection fees	No new connection or capacity charge for a conversion ADU or junior ADU, unless built with a new home.
Plan check and permit	LADBS fees are based on the project's valuation. Lower with a standard plan, because LADBS reviews only the site-specific items.
Plan set	A private firm's pre-approved plan is bought from the firm at the firm's price. The three LA County plans for unincorporated areas are free.

Interior livable space means space for living, sleeping, eating, cooking or sanitation. Wall thickness, garages and decks do not count toward the 750 or 500 sq ft lines.

The costs people forget

None of these has a fixed price, so budget for them rather than guessing at them:

• A property survey if the edges of the property are not clear. The report's drawing comes from the county parcel map; a surveyor confirms the exact edges.
• A soils report where LADBS asks for one.
• Title 24 energy calculations for the plans, which the county program requires even with a pre-approved plan.
• Agency clearances before the permit is issued, such as fire and utilities.
• The separate electrical panel, the separate water shutoff and, for a conversion, the sealed or new slab.
• A contingency for what the walls hide, which matters most on a conversion of an older garage.

How to get a real number

A bid on your property is the only cost that counts. Two things make the bid faster and more accurate:

1. Run the free property report. It shows which ADUs fit, where a detached ADU can go, the fees that apply and the pre-approved plans that fit, with every fact sourced and dated.
2. Ask our partners for quotes from the report. Up to three architects or builders who work in your area reply within two business days, and you choose who to talk to.

A guide is a starting point, not a permit. Confirm the current fees with LADBS before you build.