A new detached ADU in the Santa Clarita area typically costs about $150,000 to $350,000 or more all-in in 2026, or roughly $300 to $550 per square foot. Design, engineering, permits, and fees often add $20,000 to $40,000 or more of that total before construction starts.
These ranges come from recent Los Angeles-area cost data listed under Sources. They aren’t quotes, and your lot can move the number a lot.
How much does a detached ADU cost by size?
| Size | Typical all-in cost |
|---|---|
| 400 to 500 sq ft studio or 1-bedroom | about $150,000 to $220,000 |
| 600 to 750 sq ft 1-bedroom | about $200,000 to $280,000 |
| 800 to 1,000 sq ft 2-bedroom | about $260,000 to $350,000+ |
Smaller units cost more per square foot because a kitchen and bathroom cost about the same in any size unit. Staying at 750 sq ft or less also avoids impact fees.
Where does the money go?
Soft costs (before construction)
- Design and engineering: about $8,000 to $25,000, including the Title 24 energy report
- Permits and plan check: commonly $8,000 to $15,000 for a 600 sq ft ADU in California
- School fees: charged per square foot on new living space over 500 sq ft
- Utility connection fees: vary by provider and project
- Soils report and survey: often needed on sloped or unusual lots
Construction
- Site work and foundation
- Framing and roofing
- Plumbing, electrical, and heating and cooling (mini-splits are common)
- Insulation, drywall, and finishes
- Utility trenching to the main lines
- Fire sprinklers, if the main house requires them
Finishes are the biggest lever you control. Durable mid-range finishes usually make the most sense for a rental.
What pushes the price up or down?
Up: sloped lots, retaining walls, long utility runs, septic work, difficult access, custom architecture, two bathrooms, and high-end finishes.
Down: flat lots, simple rectangular plans, stock or pre-approved plans, standard finishes, and comparing more than one detailed bid.
How does a detached ADU compare with other types?
| ADU type | Typical total cost |
|---|---|
| Junior ADU | about $50,000 to $120,000 |
| Garage conversion | about $100,000 to $220,000 |
| Prefab, installed | about $120,000 to $320,000+ |
| Detached site-built | about $150,000 to $350,000+ |
A detached ADU costs the most, but it offers the most privacy and is usually the most flexible for renting or family use.
How do you keep a detached ADU on budget?
- Use a fixed-price contract with a detailed scope and list of exclusions.
- Freeze the design before you submit for permits.
- Hold a 10% to 15% contingency and don’t spend it in advance.
- Choose finishes within the allowances during selection, not after.
- Name one decision-maker so questions get answered quickly.
Want a real price for your lot?
Call (661) 486-8393. If no one answers, leave a voicemail with your name, phone number, address, and the type of ADU you want. You can also use the contact form. We’ll pass your details to a local ADU contractor, who will follow up with you directly. There’s no obligation to hire.
Detached ADU cost FAQs
What is the cost per square foot for a detached ADU?
Roughly $300 to $550 per square foot in the Los Angeles area, with smaller units at the higher end.
Do I pay impact fees on a detached ADU?
Not if it’s 750 sq ft or less. Larger ADUs can be charged proportional impact fees, and from January 1, 2027, SB 1117 limits fees on the first two ADUs to the space above 750 sq ft.
Is a detached ADU worth the extra cost?
It depends on your goal. A detached unit gives the most privacy and often the highest rent, but a garage conversion or JADU costs less. See renting out your ADU for the rental math.
How long does a detached ADU take to build?
Usually about 8 to 14 months from planning to move-in. See how long it takes to build an ADU.