The unit itself is the part most people focus on when planning an ADU project. But the work that happens before the unit arrives — site preparation — is where the most significant cost and schedule variables live.

This guide covers what site prep actually involves, what drives the cost range, and what to check on your own property before you start planning.

What Site Prep Covers

Site preparation for a prefab ADU delivery includes five categories of work:

1. Access Route Preparation

Your unit arrives on a flatbed truck. That truck needs to reach your backyard — which means a clear, level path at least 10–12 feet wide, with no overhead obstructions below 14 feet.

Most standard lots have adequate access from the street through a side yard gate. Tight lots may require temporary fence removal, tree trimming, or the use of a crane for placement. Crane delivery adds $1,500–$3,500 to the project cost.

Check your lot: Walk the route a truck would take to your backyard. Note anything that narrows the path or creates overhead clearance issues.

2. Foundation Work

Every Kasita unit is placed on one of three foundation types:

Concrete perimeter foundation: Most permanent option. Required by some jurisdictions for ADUs on permanent lots. Runs $4,000–$8,000 depending on soil conditions and local labor rates.

Concrete pier foundation: Appropriate for most residential lots. Faster and less expensive than a perimeter foundation ($2,500–$4,500). Fully permitted and inspected.

Compacted gravel pad with tie-downs: Appropriate only for units on wheel bases (mobile home classification). Least expensive ($800–$1,800) but not all jurisdictions permit this for long-term residential use.

Check your lot: Note any visible slopes, soft soil, or drainage issues. Sloped lots may need leveling work before foundation installation.

3. Utility Connections

Connecting your ADU to your home's existing utilities is typically the most complex and variable part of site prep.

Electrical: A new subpanel and circuit run from your main panel to the ADU location. Cost depends on distance and whether your main panel has capacity. Most standard residential panels have room for a 60-amp ADU subpanel; older panels may need upgrading. Typical cost: $1,800–$4,000.

Water: A new water supply line runs from your main line to the ADU. Cost depends on distance and whether you're sharing your existing meter or installing a new one. Typical cost: $1,500–$3,500. Some jurisdictions require a separate water meter for rental units.

Sewer: A new drain line connects to your existing sewer lateral or septic system. This is often the most expensive utility connection, particularly on lots where the sewer line runs deep or at significant distance. Typical cost: $2,500–$6,000+.

Check your lot: Locate your main electrical panel, main water shutoff, and sewer cleanout. Estimate the distance from each to your proposed ADU site. Longer distances equal higher connection costs.

4. Grading and Drainage

Your ADU site needs to be reasonably level — within 6 inches of grade across the footprint — and designed so water drains away from the unit, not toward it.

On flat, well-drained lots, grading is minimal. On sloped or poorly drained lots, grading work can add $2,000–$8,000 to the project.

Check your lot: After a rainstorm, where does water pool? Does your backyard slope toward the house or away from it? These patterns predict drainage work requirements.

5. Permit Fees and Inspections

Separate from construction costs, permit fees for a California ADU project typically run $1,500–$5,000. This includes plan check fees, building permit fees, and utility connection inspection fees.

How to Estimate Your Site Prep Cost

Use this rough checklist to gauge where your project falls:

What the Free Evaluation Covers

During your free property evaluation, we review all of the above. We walk your lot (in person or via site photos and satellite review), identify the key variables, and give you a realistic site prep cost estimate before you commit to anything.

This is the most valuable thing you can do before budgeting an ADU project. Surprises in site prep are the single most common cause of projects running over budget.

Book your free evaluation — it takes 20 minutes and costs you nothing.