Costs & Budgeting
ADU Cost Per Square Foot in 2026: Real Costs by Type & State
See real ADU cost per square foot in 2026 by type, size, and state. Compare detached, attached, garage, and prefab — with worked budget examples.
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Costs & Budgeting
Real ADU costs in 2026 by type, size, and region — including hidden fees, permit costs, and site-work that most quotes leave out.
Most ADU cost articles online quote a single "national average" and call it a day. Real ADU budgets don't work that way. The true all-in cost depends on the build type (garage conversion, detached new build, prefab, modular), the size in square feet, your local labor and permit market, what's already on your lot, and the finish level you choose. Our cost guides break each of those out and show worked budget examples — including the line items most quotes hide, like utility hookups, impact fees, site work, design and engineering, and the often-overlooked "soft costs" that add 10–20% on top of the contractor bid. Use these guides to set a realistic budget before you talk to a builder, not after.
What you'll find in Costs & Budgeting
- Real all-in costs by ADU type — detached, attached, garage conversion, JADU, prefab and modular
- Cost per square foot from 300 sq ft studios up to 1,200 sq ft two-bedroom builds, with regional adjustments
- Hidden line items — utility hookups, capacity charges, impact fees, design fees, and site work
- How to read a contractor bid and what "installed" actually means with prefab and modular units
- Worked budget examples for the most common build paths in 2026