How Much Does It Cost to Build an ADU?

How Much Does It Cost to Build an ADU?

So how much does it cost?

Building an accessory dwelling unit (ADU) is a smart investment, but it is essential to understand the full range of costs before you begin. On average, professionally built ADUs range from $60,000 to $285,000.

The final price tag depends on several important factors, including structure type, square footage, labor, materials, and location.

1. ADU Type Matters

Modern detached ADU exterior

  • Basement or Garage Conversion: $60,000 to $150,000
  • Attached ADU: $100,000 to $216,000
  • Above-Garage ADU: $128,000 to $225,000
  • Detached New Construction: $110,000 to $285,000

Conversions tend to cost less because they reuse existing space. Detached ADUs are the most expensive but offer the most privacy and design flexibility.

2. Size Drives the Budget

ADU interior kitchen space

Construction costs typically fall between $150 and $300 per square foot, though premium finishes can drive prices higher.

  • 400 sq ft: $60,000–$120,000
  • 600 sq ft: $90,000–$180,000
  • 1,000 sq ft: $150,000–$300,000
  • 1,200 sq ft: $180,000–$360,000

Keep in mind: a smaller, efficient layout often costs less per square foot when site work and systems are streamlined.

3. Labor and Materials Are Major Costs

Construction workers building an ADU

Labor often makes up 40% of total costs, while materials account for as much as 50%. Hiring specialists—like electricians, plumbers, and architects—is vital but adds expense.

4. Design, Permits, and Utilities

Design and permitting typically add 10–20% to the total budget. Utility hookups—plumbing, HVAC, electrical—can cost an additional $5,000 to $15,000.

For faster approval, consider permit-ready ADU plans that meet local code requirements.

5. Location Changes Everything

ADU costs vary widely by region. A 600 sq ft detached ADU in Los Angeles may range from $150,000 to $375,000. In contrast, the same unit in Portland or Indianapolis could cost between $115,000 and $250,000.

Local labor rates, material availability, permitting fees, and land constraints all impact the bottom line.

Ready to Build? Start with the Right Plan

Blueprints for an ADU house plan

Choosing a smart house plan can help you save time and money. Whether you’re building a rental property or a guest suite, starting with a proven design simplifies construction and permitting.

Explore curated ADU plans at adupatterns.com/collections/house-plan to find layouts that match your goals and budget.

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