These are good times for U.S. landlords. For many tenants, not so much. With demand for apartments surging, rents are projected to rise for a fifth straight year. Even a pickup in apartment construction is unlikely to provide much relief anytime soon. That bodes well for building owners and their investors. Yet the landlord-friendly trends will likely further strain the finances of many renters. That’s especially true for the 50 percent of them who already spend more than one-third of their pay on rent. A 6 percent rise in apartment rents between 2000 and 2012 has been exacerbated by a...