SAN FRANCISCO — New York-based Broadway Partners has unveiled plans to redevelop 188 Spear Street in San Francisco. The company plans to add four floors atop the existing nine-floor office building. The 105,000-square-foot addition will feature 9-foot finished ceilings, door-to-ceiling windows and views of the Ferry Building and San Francisco Bay. The redevelopment project also includes the renovation of the lobby and major upgrades to convert the existing structure into a larger, highly effective, Class A office building. The new portion is designed by Brereton Architects. Upon completion, the building will feature 13 floors and approximately 253,000 square feet of space. The property was formerly known as 120 Howard.