Figure 1: Existing slab and roof framing with proposed new slab elevation and raised roof slab. Credit: LEVENBETTS
“ The siting of new and existing buildings has become a key part of the process, especially considering the ever-changing building code-prescribed flood elevations embedded in current design standards. ” ground-floor slab below the design flood elevation? There is a one-story public building in the Red Hook neighborhood of Brooklyn that sits within an AE flood zone, with a ground-floor slab that is 3’-6” feet below the design flood elevation set by FEMA and the New York City Building Code. The public use of the building requires it to be dry-floodproofed (meaning the designers need to create a waterproof box and divert potential flood waters away from the interior of the structure). The brutalist approach is to build concrete walls around the building with the top of the wall at the design flood elevation and to create a bunker so that no water gets inside; the problem is no light gets inside either and as a result, no one wants to go inside the building at all (and this is why engineers need architects).
I believe that the solution is to raise the ground-floor slab and the existing roof. Raising the ground-floor slab is a bit of misnomer; holding down the hydrostatic pressure from flood loads so that the building doesn’t float away with a whole lot of additional concrete would be far more accurate. Simply put, the design team proposed adding a new, much heavier slab at the ground floor to push floodwater back down when it tries to push up from under the existing slab. Figure 1 above shows the trickier part of the equation. As noted above, the design flood elevation and proposed top of the exterior flood wall is 3’-6” above the top of the existing slab which would leave less than 4’ of space from the top of the exterior flood wall to the underside of the existing girders, as well as less than 6’-0” from the top of the new slab to the underside of the existing framing, neither of which are desirable. The designers proposed raising the existing roof by 6’-2 ¾” to create the necessary head clearance in the interior and the desired aesthetic on the exterior. The result is a flood-resilient structure that provides the light and access required by the Red Hook constituents who will use and fund upgrades to the existing building. continued on page 20
SEPTEMBER 2021 | PAGE 19
