Revised flood maps for New York City, when they take effect in 2016, will apply to more than 70,000 buildings, 532 million square feet of interior space, and 400,000 residents. That creates a complicated problem, because in New York's elaborate built environment, the structures involved include everything from bungalows to mid-rise apartment buildings.

This month, the city's office of Recovery and Resiliency released guidelines to help city dwellers assess their options, and make decisions about how to adapt to changing conditions. Next City reports on the city's effort (see: "Prepping for the Next Superstorm, NYC Tries to Fill in FEMA's Blanks," by Sarah Goodyear).

"The report walks property owners through the entire retrofit process: assessing flood risk; reviewing codes and regulations; coming up with a flood-mitigation strategy; and identifying short-term adaptation strategies," Next City reports. "It then outlines case studies for the varied types of building stock found at the watery edges of New York."

The city's document (see: "Retrofitting Buildings for Flood Risk") gives a general sense of the scope and character of the retrofitting problem. But it is far from comprehensive. On the contrary, it's sketchy enough to leave the reader scratching his or her head and saying, "Sure. Good idea. But how are we supposed to do that?"

One option New York City authorities contemplate for attached housing is an “elevate and wet floodproof” strategy, indicated by the drawing at top. The idea is to relocate living activities to new stories added to the upper part of the building, while adapting the stories below the flood elevation with water-tolerant materials and assemblies.
One option New York City authorities contemplate for attached housing is an “elevate and wet floodproof” strategy, indicated by the drawing at top. The idea is to relocate living activities to new stories added to the upper part of the building, while adapting the stories below the flood elevation with water-tolerant materials and assemblies.
Another strategy, “wet floodproofing,” is roughly indicated by the red box in the lower drawing. In this approach (which is not approved for residential uses), the areas below the flood line would in theory be retrofitted to hold water out and stay dry, even in a repeat of Sandy’s flooding — or worse.
Another strategy, “wet floodproofing,” is roughly indicated by the red box in the lower drawing. In this approach (which is not approved for residential uses), the areas below the flood line would in theory be retrofitted to hold water out and stay dry, even in a repeat of Sandy’s flooding — or worse.

Take, for example, the document's section for "Attached" housing, typified by the classic New York City brownstone row house. The report shows a cutaway drawing of a building whose lowest occupied floor is four feet below street level. The flood elevation for the area is a dotted line two feet above the second floor — leaving the entire first floor, and the cellar below that, under water in case of a flood. The document suggests several options, including "elevate" (which in this case does not mean lifting the building, but simply adding two stories on top of the existing roof), "wet floodproof" (which involves essentially moving out of the lower two stories and putting an addition on the back to replace the lost square footage), and, audaciously, "dry floodproof" (an option which would somehow make the second floor, below grade first floor, and fully subterranean basement completely water-tight in the event of a 12-foot-deep ocean storm surge). With regard to the "dry floodproofing" strategy, the document offers this dry advice: "Add reinforcement to roof, party-walls, exterior walls, and foundation walls and slab. Ensure changes to party-walls do not impact neighboring property's structural integrity."

Dry floodproofing, the document notes, is not permitted for residential use.

Plainly, the city's latest document is not intended to provide answers, but to indicate the nature of the problem the city faces, and to point the way to workable solutions. It remains to the professionals to work out the details, case by case. Along the way, New York officials say, the city's architects, engineers, and contractors will learn lessons that other cities may find useful. Said Carl Weisbrod, director of New York's department of city planning, 'We hope that this study can be used as a resource not only in New York, but in other coastal cities with similarly diverse building types."