The number that stops most people in their tracks is the unit price. Ours starts at $22,000. But the total cost of building a backyard ADU includes more than the unit itself — and the gap between "starting price" and "total project cost" is where homeowners most often get surprised.

This post lays it all out. The full cost range, where the variables are, and what you can do to keep your project on the lower end of the range.

The Four Cost Categories

Every ADU project has four cost buckets. Understanding each one helps you budget accurately from the start.

1. The Unit Itself: $22,000–$35,000

This is the prefab unit — designed, built, and finished in our facility. What's included:

• All structural framing, wall panels, and roof assembly

• Exterior cladding and roofing

• Windows and exterior doors

• Interior finishes (flooring, walls, ceilings)

• Cabinetry and fixtures

• Electrical panel and rough-in

• Plumbing rough-in

• HVAC rough-in

• HCD certification and compliance documentation

What varies the price within this range: square footage, finish level, and options like upgraded appliances, bathroom configuration, or the wheel-base option.

2. Delivery and Placement: $1,500–$4,000

Delivery costs depend on your distance from our facility and the accessibility of your lot. Crane placement (required when cranes are needed for tight lots) adds to this cost. Most deliveries fall in the $2,000–$3,000 range for California locations.

3. Site Preparation: $3,000–$15,000

This is the widest range and the most variable category. Site prep includes:

Foundation: A concrete perimeter foundation runs $4,000–$8,000. Concrete piers (appropriate for many lots) run $2,000–$4,000. Gravel pads (for units on wheel bases) run $1,000–$2,500.

Utility connections: Connecting to water and sewer typically runs $2,000–$6,000 depending on distance from existing hookups and local permit fees. Electrical connection runs $1,500–$3,500.

Grading and drainage: If your lot has slopes or drainage issues, site grading can add $2,000–$6,000. Flat, accessible lots avoid this cost entirely.

The single biggest variable: how close your lot's existing utilities are to your proposed ADU site. We check this in your free evaluation so there are no surprises.

4. Permits and Fees: $1,000–$8,000

California has reduced impact fees on ADUs under 750 sqft significantly, but permit fees, plan check fees, and school fees still apply. In most California jurisdictions, total permit costs for a prefab ADU run $2,000–$5,000.

Total Project Cost Ranges

Putting it together:

The $22,000 unit price is real. The total project cost is higher — but it's still a fraction of what a custom ADU build costs ($120,000–$200,000+ in California today).

Where People Overspend

Not evaluating the lot first. Site prep surprises are the #1 cause of budget overruns. A free property evaluation catches these before you commit.

Over-specifying the unit. Our standard finishes are solid. Upgraded appliances and premium finishes add cost without meaningfully improving rental income or resale value.

Using the wrong foundation type. Concrete perimeter foundations are not always necessary. For many lots, concrete piers or a gravel pad with tie-downs is structurally appropriate and significantly cheaper.

How to Get an Accurate Quote

The only way to get an accurate total project cost is to have someone look at your specific lot. That's what our free property evaluation is for — we review your property, identify site prep requirements, check utility proximity, and give you a real number range before you make any commitments.

No sales pitch. Just a straight answer.