350 Mission Street

To reduce the building’s carbon footprint, Mark Sarkisian, SOM’s structural engineer, set about reducing the gravitational weight of the materials used to construct it. To this end he devised a system of bundling discarded plastic bottles and other lightweight waste products in stabile blocks that could supplant heavy concrete in areas of the building’s floors that do not contribute directly to structural support.

Blocks of discarded plastic bottles to be imbedded in concrete floor slabs

Other examples of waste materials compacted into blocks used to lighten concrete floorslabs

The floors lightened with blocks of recycled debris will significantly improve the structure’s energy economy. For the building’s occupied 450,000 square feet, the savings will be about 5,400 cubic yards of concrete, enough to lay about 20 miles of residential sidewalk. The amount of steel projected, but not used, for rebar and post-tensioning needs would be equivalent to about 8,000 refrigerator or 1,000 cars.

A section showing the spaces between the floor surfact and the slab where the blocks can be used

Another major savings will come from the installation of the HVAC system between the functional floors and the structural floor slabs, as shown below. This arrangement will both enable the creation of discrete zones for heating and cooling as needed and increase the floor-to-floor dimensions along with the amount of daylight admitted to the interiors.

The HVA,C system

Although the ground seems solid, even immovable, under Fremont and Mission Streets, the manmade surface covers a  semi-fluid mass of bay mud permeated by tide water with a constant temperature of 65 degrees that cycles through the area twice a day. To use this reliable source of water for geo-thermal energy, the mechanical engineers at WSP Flack+Kurtz designed a grid of pipes set in a concrete slab beneath the building’s underground garage. This mechanical system provides radiant heating and cooling, shown in red, for the lobby floor above.

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