This week the Seattle Art Museum closes its main building for 16 months to construct an expansion. “Downtown, the museum will have 300,000 square feet, tripling the exhibition space and providing a free-admission, wrap-around public corridor full of art and art events. Besides that, there’s plenty of room for further expansion. The building is 16 stories high, and initially the museum will occupy only the bottom four floors and rent out the rest to Washington Mutual. When SAM needs more room, it can hand the bank its walking papers for eight more floors. (The top four belong to the bank.)”