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CALCULATOR

California ADU Construction Cost Calculator

Building an Accessory Dwelling Unit (ADU) in California involves various factors that impact the overall cost. 
 

Your costs will vary depending on unit size, location, lot conditions, building and safety regulations, zoning requirements, and personal preferences like fit and finish.

The main factors that impact ADU construction costs are:

  1. ADU Size

  2. Construction Type

  3. Lot Slope

  4. Utilities & Finishing

  5. Soft Costs

  6. Contingency

ADU Size: 
Larger ADUs tend to have a lower cost per square foot due to the spread of construction costs over a larger area. Our calculator adjusts costs accordingly, with initial square footage costing more per unit area.

Construction Type:
ADU construction costs vary based on whether it's a conversion or new construction. Conversions typically cost less as they reuse existing structures, while new constructions incur additional expenses like fire sprinklers and solar panels.

 

  • CONSTRUCTION TYPE|
    AVERAGE COST / SQ FT

  • Conversion (attic, basement, etc.)
    $125 - $200+

  • Attached ADU
    $150 - $250+

  • Detached ADU
    $180 - $300+

  • Building ADU over existing structure
    $200 - $350+

Lot Slope:
Building on a sloped lot can increase costs by 25% due to grading, soil compaction, and additional structural support requirements.

 

Utilities & Interior Finish:
Costs vary based on the level of finish, ranging from basic to premium, impacting electrical, plumbing, HVAC systems, appliances, and interior elements.

 

FINISH LEVEL - AVERAGE COST / SQ FT

Basic                   $10 - $20

Standard            $20 - $40

Premium            $50+
 

Soft Costs:
These include planning, design, engineering, permitting, and application fees, as well as utility fees and project management expenses.

 

SERVICE - AVERAGE PRICE

Design
$2,000 - $30,000+

Architectural Plans
$2,000 - $40,000+

Engineering
$0 - $5,000+

Permits & Application Fees
$1,500 - $8,000+

Impacts Fees
$2,000 - $14,000+

Utility Fees
$0 - $20,000+

Project Management
$2,000 - $25,000+

 

Contingency: It's advisable to set aside a construction contingency of at least 10% to cover unexpected costs, such as rising material prices and supply chain delays.

By considering these factors, our calculator provides a comprehensive estimate to help you plan your ADU project effectively.

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​ Burbank, California
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