How Much Does an ADU Cost in Los Angeles?

The two ways ADUs are priced, and why it matters

You will see ADU construction in Los Angeles costs quoted two different ways, and mixing them up is the most common reason people end up with a wildly wrong expectation.

A ground-up build (new construction, whether attached to the house or standing alone in the yard) is priced per square foot. That makes sense, because you are choosing the size, and every extra square foot costs roughly the same as the last one.

A garage conversion is priced as a whole project. That also makes sense, because you are not choosing the size: the garage is the size it is. Most of the cost sits in bringing an existing structure up to a habitable standard, and that work does not scale neatly with floor area.

So a per-square-foot figure and a whole-project figure are not comparable, and a contractor quoting one when you were asking about the other is a conversation worth slowing down.

Every verified range in one table

Every range on this page, in one place. Construction and plans-plus-permitting are always quoted separately, because they are two different pieces of work.

Ground-up ADU: the construction range

For a one-story ADU, attached or detached, construction runs $280 to $320 per square foot. For a two-story detached ADU, $285 to $320 per square foot.

Those two ranges are close, and the reason is worth understanding: a two-story unit uses less land and less foundation per square foot of living space, which offsets the cost of the second storey. Building upwards is not the premium option people assume it is, and on a constrained lot it is frequently the only way to get the space.

We are deliberately not multiplying those rates by a unit size to show you a total. A total produced that way looks authoritative and is not. It would be our arithmetic, not a price anyone has approved, and it would be wrong for your property in ways the multiplication cannot see. What the range is genuinely good for is telling you the order of magnitude, and whether this is a project for this year.

Garage conversion: the whole-project range

For a typical 400 square foot garage, construction is $90,000 to $110,000 for an attached garage and $90,000 to $120,000 for a detached one.

Not every 400 square foot conversion falls inside those ranges. A sound, dry, attached garage with services close by sits at the bottom; a detached structure with failing footings, no nearby supply and a roof that needs replacing sits above the top.

The reason a conversion undercuts a new build is that the slab, the walls and the roof already exist. The reason it is still a six-figure job is everything else: insulation, windows, a habitable floor, plumbing, an upgraded electrical supply, heating and cooling, closing up the garage door opening, and then a kitchen and a bathroom.

Plans and permitting are always priced separately

Plans and permitting are quoted as their own line on every Yeganeh project, and never folded into a construction figure.

That is not an accounting preference. They are separate pieces of work, they happen at different times, and some homeowners deliberately do the first without committing to the second: getting a property designed and permitted, then building when finances allow.

The ranges: $5,000 to $7,000 for an attached garage conversion, $5,000 to $10,000 for a detached one, $7,000 to $12,000 for a one-story ADU, and $12,000 to $16,000 for a two-story ADU.

One thing these do not include is city permit fees themselves. We have not itemised what a plans package covers, and we would rather say so than imply an inclusion that turns out not to apply to your jurisdiction.

• Attached garage conversion: $5,000 to $7,000
• Detached garage conversion: $5,000 to $10,000
• One-story attached or detached ADU: $7,000 to $12,000
• Two-story detached ADU: $12,000 to $16,000

What actually moves the number on your property

Two identical-looking projects on the same street can land at different ends of the range. These are the reasons, roughly in order of how much they matter.

• Site conditions: What is under the ground, how far the utilities have to travel, whether machinery can physically reach the back of the lot, and what has to come out before anything goes in. This is the largest single source of variation and the one that is hardest to judge from a photograph.
• Scope: Whether the project is a conversion, an extension of an existing structure, or an entirely new building. And whether the main house is being touched at the same time.
• Storeys and structure: A second storey changes the foundation and framing requirements. So does building over or beside an existing structure that was never designed to carry anything.
• Finishes: The only line you control completely. Cabinetry, stone, flooring, fixtures and appliances are where a project moves within its range rather than outside it.
• Jurisdiction: Requirements, review times and conditions differ between cities and, in places, street to street. This affects the permitting timeline more than the construction cost, but it does affect both.

How long the money takes to spend

Permitting often takes approximately two to three months, depending on the city and the project. A garage conversion commonly takes around three months to build after that, depending on scope and site conditions.

For ground-up ADU construction there is no single honest range. Duration depends on size, on one storey versus two, on site conditions, design complexity, jurisdiction and scope, and any builder quoting you a universal figure for it is quoting a marketing number. We give you a property-specific timeline after reviewing your site and scope.

Getting a number that is actually yours

Everything above is guidance. The number that matters is the one for your property, and getting it involves someone standing on the lot.

That visit is free, and so is the estimate that follows it. There is no obligation attached and no charge if you decide the project is not for you, which some people, having seen real ranges rather than a teaser price, reasonably do.