Free ADU Cost Calculator — Estimate Your 2026 Build
How much does an ADU cost? Building an ADU typically ranges from $80,000 to $500,000 depending on size, type, and location. Use our free ADU cost estimator to calculate what you'll pay in 2026 — enter your city, ADU type, and square footage for an instant cost range based on local construction data.
Calculate Your ADU Construction Cost
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Additional Features
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Cost Summary
Construction Breakdown
Estimated Soft Costs
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Understanding ADU Construction Costs
The cost to build an ADU varies significantly based on the type of unit. Here is a breakdown of average ADU building costs for 2026.
Detached ADU
Stand-alone backyard cottages offer the most privacy and rental value but have the highest construction costs due to new foundation and utility requirements.
Garage Conversion
Converting an existing structure is often the most affordable ADU cost option, utilizing the existing shell and foundation to save money.
Attached ADU
Building an addition connected to your main home allows you to share walls and utilities, typically costing less than a detached unit.
ADU Cost by Type
Garage Conversion
The most affordable entry point. Converting an existing structure saves on foundation and framing costs.
Prefab ADU
Factory-built units offer predictable prefab adu costs and faster on-site installation timelines.
Custom Detached
A completely custom backyard cottage designed for your specific lot and needs. Highest flexibility.
Above Garage
Building a second story DADU above a garage is complex but preserves yard space.
Factors That Affect Your ADU Cost
How to Reduce Your ADU Construction Costs
Building an ADU is a major investment, but smart planning can save you tens of thousands of dollars.
- Choose a simple rectangular design to minimize corners and roof complexity.
- Use standard material sizes to reduce waste and labor.
- Locate your ADU close to existing sewer/water lines to reduce trenching.
- Consider 'stock' or pre-approved plans instead of full custom architecture.
- Keep the design within standard size limits (e.g., <800 sq ft) to avoid impact fees in some cities.
Did you know?
Financing is often the biggest hurdle. Many homeowners use a HELOC, renovation loan, or cash-out refinance to fund their project.
*Based on a $200k loan at current rates. Rental income often covers this cost entirely.
Frequently Asked Questions About ADU Costs
Done Estimating? Track Your Real Costs.
TerraLine picks up where the estimator leaves off — track actual spend vs budget, manage draw schedules, and know exactly where every dollar goes during construction.
Next Steps After Calculating Your ADU Cost
Get Contractor Quotes
Connect with vetted local contractors to get accurate bids for your specific project.
Explore Financing
Learn about HELOCs, construction loans, and grants available for ADU projects.
Check Requirements
Verify zoning, setbacks, and size limits for your specific city and lot.