Greenlite Glass Systems photo by James Wu

The Salesforce Transit Center is now open in San Francisco after nearly a decade of construction. Designed by Pelli Clarke Pelli Architects, the $2.26 billion transit center is being hailed as the “Grand Central Station of the west.” The walkable skylight and light columns developed by Greenlite Glass Systems Inc. and Vetrotech Saint-Gobain are a major part of the design that were almost removed from the design.

The largest of the light columns forms the central element of the primary public space within the center called the Grand Hall. The column reaches from the park all the way down to the train platforms two stories below grade, providing light to all areas of the 1.2 million-square-foot transit center.

Ryan Dennett, owner of Greenlite Glass Systems, says that the feature was almost value engineered out of the project because it would be expensive, but the architect was adamant that it remain in the design due to the natural light it brings into the center, which spans five city blocks at the base of Salesforce Tower.

Contraflam Liteflam XT 120, a walkable fire-rated glass floor and skylight system, was developed specifically for this project.

Greenlite Glass Systems photo by James Wu

“What makes this unique is that it’s a two-hour, fire-rated system that is blast resistant,” says Dennett. “Because the product is used on the exterior, it has to have a backup gutter system. We used structural silicone joints as well.”

Kevin Norcross, general manager at Vetrotech Saint-Gobain, says Contraflam Liteflam XT 120 is an entirely new product that came from a collaborative process. Vetrotech worked closely with Greenlite Glass Systems, glazing contractor Crown Corr and Pelli Clarke Pelli on a design assist to ensure that all the extreme structural and safety requirements were taken into account.

“Because of its location and dual function as a skylight and high-traffic pedestrian walkway, this project had several unique challenges. It had to handle live loads from above; be slip-resistant, weatherproof and water-tight; and meet strict seismic requirements for San Francisco,” says Norcross. “It had to have a two-hour fire rating—something that had never been done before in a glass floor—and easy and efficient to replace in case of damage without sacrificing safety.”

Greenlite Glass Systems photo by James Wu

The floor includes a top layer of sacrificial glass, which Norcross says is the first in the country to be tested for weather cycling.

“Should the sacrificial layer experience wear and tear or become damaged, the pane can be replaced on site without removal of the lower fire-rated portion,” he says.

The product was tested to ASTM E 119, UL 263, NFPA 251, CAN ULC-S101 and UL BXUV.C903 standards. It passed the CPSC 16 1201 test for impact safety in both categories I and II.