Booming Seattle struggles to stay affordable

FOR the third consecutive year, Seattle has the most cranes in operation of any city in America—three times as many as New York. Long a placid, drizzly company town, the place is booming. Since 2010 Seattle has grown more quickly than any other large American city, thanks in part to the success of Amazon and Microsoft, two local technology firms. Entrepreneurs are flocking there, repelled by the obscene costs of San Francisco.

But the pathologies of the Bay Area may not be far behind. Rents have shot up and homelessness is common. “We are not a welcoming city in the way Seattle has historically been,” says Mike McGinn, the former mayor. The boom shows little sign of abating, meaning that Seattle has only a few years before it contracts a case of full-blown San Francisco. Either the city will cleverly manage its growing prosperity, or it will become inaccessible to ordinary people. The Emerald City would be turned into a gilded fortress.

A single-family residence now rents for $2,...