What an ADU really costs in Los Angeles: the fees, not the price per square foot

Law verified as of 10 September 2026 against the text published by the California Legislature. Fee schedules are set by each agency and change; the statutory exemptions below do not.

Why this page does not open with a price per square foot

Because the number would be invented. ADU construction cost in Los Angeles depends on site access, slope, soil, the capacity of the existing panel and sewer lateral, fire hazard zone requirements, finish level, and what contractors are charging in the month you bid it. A page that gives you one number is giving you an average of other people’s projects, and your project is not the average.

What is knowable before design starts is the fee side. It is also where California law hands you money that many homeowners never claim, because it arrives as an absence on an invoice rather than a discount.

The exemptions the statute gives you

Fee	What the law says	Statute
Impact fees, ADU 750 sq ft or less of interior livable space	Shall not be imposed	§ 66311.5(c)(1)
Impact fees, JADU 500 sq ft or less	Shall not be imposed	§ 66311.5(c)(1)
Impact fees, ADU over 750 sq ft	Allowed, but charged proportionately to the square footage of the primary dwelling	§ 66311.5(c)(1)
School facilities fees, unit under 500 sq ft	Treated as not increasing assessable space by 500 sq ft under Education Code § 17620	§ 66311.5(c)(3)
Utility connection fee / capacity charge	The ADU is not a new residential use for this calculation, unless built with a new single-family dwelling	§ 66311.5(b)
Utility connection, conversion of existing space under § 66323(a)(1)	No new or separate connection, and no related connection fee or capacity charge, may be required	§ 66311.5(d)
Utility connection, other ADUs	Permitted, but proportionate to burden by square footage or drainage fixture unit values, and not exceeding the reasonable cost of service	§ 66311.5(e)

“Impact fee” here takes the § 66000(b) meaning plus the park fees of § 66477, and expressly excludes connection fees and capacity charges — § 66311.5(c)(2). Those are handled by the rows below it, which is why reading the two together matters.

The 750 square foot cliff

This is the single most consequential number in an ADU budget and it is not a design number.

At 750 square feet of interior livable space, impact fees are zero. At 751, you are into a proportionate calculation against the primary dwelling’s square footage. Depending on your jurisdiction’s schedule, that step can be worth more than the extra room you gained.

It does not follow that every ADU should be 750 square feet. It follows that if your design has drifted to 780, somebody should price both versions before the drawings are finished. That is a five-minute question at schematic stage and an expensive one after plan check.

The same logic applies at 500 square feet for school fees, and it is the reason JADUs — capped at 500 by definition — avoid that line entirely.

What no exemption covers

Being clear about this is more useful than optimism.

Plan check and permit fees are cost recovery for reviewing and inspecting your project. They are not impact fees and no ADU exemption reaches them.

Your side of the meter. If the existing service cannot carry another dwelling, upgrading it is your cost. A panel at capacity, a sewer lateral of marginal size or condition, or a long run from the house to a detached unit are all real numbers that do not appear in any published cost range.

Site work. Grading, drainage, retaining structures. On the hillside parcels common across the Santa Monica Mountains and the Conejo Valley, this can exceed the cost of the building it serves.

Fire requirements. Very high fire hazard severity zone construction requirements affect assemblies, materials and access, and they are not waived because the building is small.

Septic. Where you are not on sewer, § 66323(f) permits the agency to require a percolation test completed within the last five years, or ten if recertified. If the system needs upgrading, that is a project of its own.

How to get a real number

Two figures, obtained in this order.

First, the fee number, which can be made exact. Ask the permitting agency for a fee estimate against a declared valuation and insist on line items rather than a total. Then read the line items against the table above. An impact fee appearing on a 700 square foot ADU is worth querying with the section number in hand.

Second, the construction range, which cannot be made exact but can be made honest. That requires somebody to look at the actual parcel: the slope, the access, the panel, the lateral, the soil, the fire zone. Any range produced without that is a guess wearing a decimal point.

The order matters. The fee analysis can change the design — the 750 square foot line especially — and it is far cheaper to learn that before the drawings than after.