“It’s hard to miss San Francisco’s new U.S. Federal Building, a narrow 18-story office slab with a skewed, not-quite-mansard roof. Completed in March of last year, the building is a study in contradictions: an ambitious energy-conserving agenda, a tight budget, and a highly restrictive set of security concerns. How did Pritzker Prize-winning architect Thom Mayne deal with this challenging mix?”