Building an ADU in the Bay Area should be straightforward, but conflicting quotes and surprise fees leave homeowners frustrated. As a licensed Bay Area ADU builder, we analyzed 85 local projects from 2023–2026 to bring you transparent data—and explain how our integrated design-build model saves time, money, and stress. Bay Area counties 2026 ADU Cost Ranges by Type (Data sourced from 85 Bay Area projects) ADU Type Size (sq ft) Average Cost ($) % of soft cost Studio 400–600 15