ADU Cost Guide
How much does an ADU cost in California?
A straight answer, then the details. Below are starting construction prices for every layout we build across Southern California, plus exactly what those numbers include and the site costs to budget separately.
Last updated July 2026 · Reviewed by Richard Corral, ADU Concepts · Licensed California general contractor (CSLB #1018294)
In Southern California, an ADU typically costs between about $185,000 for a compact studio and $675,000 for a large three or four bedroom home, covering design, engineering, permitting, and construction. Construction alone starts from about $172,000. Most one and two bedroom backyard ADUs land in the $290,000 to $410,000 range, or roughly $365 to $690 per square foot. Smaller ADUs cost more per square foot; larger ones cost less. City fees, utility hookups, and site work are budgeted separately.
Starting prices by layout
Here is the construction price, starting from, for each ADU layout we build. Construction price includes the light-gauge steel structure, foundation, on-site erection, and standard finishes, fixtures, and appliances, built on your property. Design, engineering, and permitting is a separate line starting from $15,500, and city fees, utility hookups, and site work are budgeted separately. All of that is broken down below.
Single-family ADUs
| Layout | Configuration | Interior size | Construction from |
|---|---|---|---|
| The NookU250-01 | Studio · 1 bath | 240 sq ft | From $172,000 |
| The SuiteU400-11 | 1 bed · 1 bath | 405 sq ft | From $215,000 |
| The StudioS395-01 | Studio · 1 bath | 395 sq ft | From $249,000 |
| The CasitaS500-11 | 1 bed · 1 bath | 500 sq ft | From $275,000 |
| The PairU570-22 | 2 bed · 2 bath | 570 sq ft | From $299,000 |
| The TrioU720-32 | 3 bed · 2 bath | 720 sq ft | From $313,000 |
| The CornerS800-225 | 2 bed · 2.5 bath | 823 sq ft | From $372,000 |
| The HavenS880-215 | 2 bed · 1.5 bath | 880 sq ft | From $374,000 |
| The GemS1200-32 | 3 bed · 2 bath | 1,245 sq ft | From $475,000 |
| The GrandS1200-42 | 4 bed · 2 bath | 1,200 sq ft | From $484,000 |
| The ManorS1200-335 | 3 bed · 3.5 bath | 1,200 sq ft | From $618,000 |
Multifamily (multi-unit) buildings
| Layout | Configuration | Building size | Construction from |
|---|---|---|---|
| The TwinM800-2-21 | 2 units · 2 bed / 1 bath each | 1,600 sq ft total | From $838,000 |
| The DuoM860-2-22 | 2 units · 2 bed / 2 bath each | 1,740 sq ft total | From $853,000 |
| The StackM1200-2-32 | 2 units · 3 bed / 2 bath each | 2,400 sq ft total | From $970,000 |
| The QuadM460-4-11 | 4 units · 1 bed / 1 bath each | 460 sq ft each | Contact for quote |
Prices are starting points for standard configurations, not quotes. Two-story layouts, custom finishes, and your site and city conditions affect the final number. Multifamily prices are for the complete multi-unit building. We price every project to your specific property.
Why bigger ADUs cost less per square foot
A kitchen, a bathroom, a foundation, and utility hookups cost roughly the same whether an ADU is 300 square feet or 900. Those fixed costs get spread over fewer square feet in a small unit, so its per-square-foot price looks high even though the total is lower. As the unit grows, the same fixed costs are spread across more space, and the cost per square foot drops, from around $690 on a compact studio toward $365 on a large three or four bedroom ADU.
It is worth knowing before you assume a smaller ADU is the budget option: the total will be lower, but you are paying a premium for every square foot you build.
What the construction price includes, and what's separate
The single most common reason an ADU ends up costing more than an owner expected is a number that quietly left things out. Here is exactly where the line sits.
Design, engineering & permitting is a separate line, starting from $15,500 (larger and multi-unit layouts start higher). Add it to the construction price above for your full design-build cost.
Included in the construction price
- The light-gauge steel structure, fabricated and delivered
- Foundation and on-site frame and roof erection
- Standard finishes, fixtures, cabinets, flooring, tile, and appliances
- Built on your property by our own crews
Budgeted separately (varies by lot)
- City permit and plan-check fees (vary by jurisdiction)
- Utility hookups: water, sewer, gas, electric, roughly $40 per linear foot
- Soil, topographic, and site surveys
- Solar, where a city requires it
- Demolition and haul-away when needed, roughly $10 to $15 per sq ft
- Extra or structural foundation work, roughly $10 to $16 per sq ft
- Long utility trenching runs and difficult-access sites
Steel framing is included, not an upcharge
Our ADUs are framed in light-gauge steel as standard, and that is already built into every price on this page. It is not a premium option you pay extra for. If anything, choosing conventional wood framing tends to add cost, not save it. Steel is dimensionally stable, non-combustible, and resistant to termites and rot, which matters a great deal in California.
What moves your number
Size
The biggest lever. Larger ADUs cost more in total but less per square foot.
One story vs two
A two-story ADU fits more living space on a tight lot, with a different structural and cost profile.
Site access & conditions
We need roughly 5 feet of side clearance to bring panels in. Tight or sloped lots add cost.
Distance from utilities
The farther your water, sewer, and power runs are, the more the hookups and trenching cost.
Finish level
Standard finishes are included in these prices. Upgraded materials move the number up.
Demolition
Removing an existing garage or structure first is priced separately, per square foot.
Your city's fees & process
Permit, plan-check, and impact fees differ by jurisdiction. We navigate each city for you.
What a multifamily ADU project costs
For multifamily owners adding rental units, a complete two-unit building in our catalog starts around $838,000 in construction price for a two-bedroom-per-unit layout, up to about $970,000 for a three-bedroom-per-unit building. More compact two-unit configurations can be designed for less.
Larger densification projects, adding several detached ADUs plus interior conversions of non-livable space across an existing apartment property, are scoped per property. We will walk your building, confirm how many units state law lets you add, and put real numbers to it.
Factory-built option
What about a Boxabl Casita?
We are an authorized Boxabl dealer and installer. Boxabl publishes Casita prices from $60,000 for the Studio, unit only; your site work is priced for your lot. See the models, published prices, and how installation works.
FAQ
ADU cost questions
How much does an ADU cost in California?
How much does a backyard ADU cost?
How much does a studio ADU cost?
What is the cost per square foot of an ADU?
Why do smaller ADUs cost more per square foot?
What does the construction price include, and what is design-build?
How much does a multifamily or multi-unit ADU project cost?
Is a steel-framed ADU more expensive than wood?
Does ADU Concepts give free estimates?
How much does a Boxabl Casita ADU cost in California?
Prices on this page are starting points for standard configurations of Southern California ADUs, not a quote or a guaranteed price. Actual cost depends on your specific property, size, finishes, site conditions, and city fees. Contact us for an itemized estimate for your lot.
Want a real number for your lot?
Tell us about your property and goals. We'll give you a straight, itemized estimate, including the city fees and site costs a general range can't capture.
Explore next: single-family ADUs, browse layouts, or California ADU laws.