Jay Paul Co. has started demolition on 181 Fremont St., clearing the way for a 54-story office and residential condo building next to the Transbay Transit Center.

Once the two existing buildings are razed, the Silicon Valley developer anticipates starting construction in November on the tower, which will top off at 800 feet high and 684,000 square feet. Once completed, it will be the second-tallest building in San Francisco, after the 853-foot Transamerica Pyramid.

“We are excited to be one step closer to realizing the new vision for this emerging and vital neighborhood,” said Principal and Founder Jay Paul.

Jay Paul Co. plans to finish construction of the tower in the fourth quarter of 2015 and will pursue LEED Gold or Platinum certification.

Designed by Heller Manus Architects, 181 Fremont will be one of only two buildings that directly connects to the Rooftop Park.

Using an excavator equipped with a set of clamping jaws known as a “clam shell,” the perimeter walls and structure of the existing buildings will be excavated to the ground. The remnants will then be broken into smaller, more manageable pieces and sorted into like materials, with each type of material hauled to various handling facilities for processing and recycling. Paul said 95 percent of the existing building will be recycled.