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Construction Cost Estimator

Build a line-by-line cost breakdown for any ADU or addition project with adjustable soft costs and contingency.

How the Cost Estimator Works

Start by selecting one of six project types: detached ADU, attached ADU, garage conversion, room addition, floor addition, or basement conversion. Enter your planned square footage and cost per square foot, then add soft costs for permits, architectural design, utility connections, site prep, and landscaping. Set a contingency percentage and the tool calculates your total all-in build cost instantly.

  • Six project types with different default cost profiles
  • Hard cost = square footage multiplied by cost per sqft
  • Five soft-cost line items: permits, design, utilities, site prep, landscaping
  • Adjustable contingency percentage (default 10%) applied to hard costs
  • Total build cost updates in real time as you change any input

Why Accurate Costs Matter

The biggest mistake in ADU and addition projects is underestimating costs. Permit fees alone can range from $2,000 to $20,000 depending on your jurisdiction. Utility hookups for detached ADUs often run $5,000 to $15,000. By itemizing every cost category upfront, you avoid the surprise overruns that turn a profitable project into a money pit.

  • Prevent cost overruns by planning every line item before you start
  • Compare detached vs. attached ADUs to find the most cost-effective option
  • Adjust contingency to stress-test your budget against unexpected expenses
  • Use local contractor bids to refine your cost-per-sqft estimate

Sample Output

See what this feature calculates for you.

Construction Cost Estimator
Hard Cost (600 sqft x $200) $120,000
Permits + Design $13,000
Site Prep + Utilities $8,000
Contingency (10%) $12,000
Total Build Cost $143,000

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