When all’s said and done, the 55-story skyscraper at 181 Fremont will (briefly) be the second-tallest tower in San Francisco.

It’s not easy making such a tall building.

At 800 feet, the 181 Fremont will clock in just 53 feet shy of the Transamerica Pyramid, and both will be eclipsed by the Salesforce Tower when that reaches completion. The $500 million highrise will feature 36 floors and 404,000 square feet of office space, while the top 17 floors will be home to 67 luxury condos, all developed by the Jay Paul Co.

Constructing any skyscraper of that scale is difficult, but Level 10 Construction has had some extra complications.

“It’s an incredibly difficult site because of the constraints with the property lines, the Transbay construction, and only having access to Fremont street, which is one of the busiest streets in San Francisco,” said Steve DeWees, Level 10 Construction’s project executive.

With the Transbay Terminal on one side, the building at 199 Howard on another, and a pedestrian walkway on a third side, the builders only have direct access to 181 Fremont from the busy street side, which has necessitated some creative traffic problem solving. After extensive talks with the city, Level 10 Construction was allowed to lease (at a cost of several hundred thousand dollars) the parking lane on the opposite side of the street and turn it into a drive lane. This allowed them to close off the lane closest to their site for delivery trucks without severely constricting traffic. Another challenge is the caissons.

The structure, designed by Heller Manus Architects, will have the deepest caissons — part of the foundation of buildings and bridges — of any building in the city.

“We went on average about 260 feet from the bottom of the caissons to street level,” DeWees said. “As far as anyone can tell, those are the deepest ones in the city with the exception of those that were done for the Bay Bridge.”