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Patrick Collison (tweeted 2026-05-05) defines “trapped buildings” as structures…
Brief
Patrick Collison defines “trapped buildings” as structures that would not meet today’s zoning/codes yet are legally protected from substantial alteration or demolition. He solicits estimates for major cities; Anthropic Claude replied that San Francisco likely has about 100,000 such buildings (roughly two-thirds), with a 70,000–130,000 plausible range.
Why it matters
Patrick Collison (tweeted 2026-05-05) defines “trapped buildings” as structures that could not be built today under current zoning and code rules but also cannot be substantially modified or demolished because of historic-protection rules.
Key details
- Anthropic Claude estimated San Francisco has roughly 100,000 trapped buildings—about two-thirds of the city's physical structures—with ‘moderate’ confidence and a plausible range of 70,000–130,000 depending on how “can't be substantially modified” is operationalized.
- Collison asks whether anyone has estimated the fraction of buildings in other major cities that fall into this category, highlighting a gap in comparative estimates or research.