Seattle's tallest residential tower, 1521 Second Avenue, will begin rising this summer. The 440-foot glass-and-steel tower will be the first tower to be designed and completed under the city's new downtown zoning regulations, which encourage urban density through taller and more slender buildings. Mayor Greg Nickels signed the zoning legislation on April 12. The 38-story tower will contain 143 condominium units. Opus Northwest of Minneapolis is developing the property along with local developer William Justen. Seattle-based Weber + Thompson is the design architect. Opus is the architect of record and general contractor. Scheduled completion: 2008.