Two Kinds of Flood, One Building
New York City floods in two different ways, and a building has to be ready for both.
The first kind comes from the sea. Coastal flooding follows the tides and storm surge, and it returns to the same low-lying waterfront neighborhoods. Hurricane Sandy in 2012 is the best-known example, and places like Red Hook have spent years since rebuilding with resilience in mind.
The second kind comes from the sky. A cloudburst, meaning a sudden and intense downpour, can hit any neighborhood, including ones far from the water. The city's stormwater system handles roughly an inch and a half to an inch and three-quarters of rain an hour. When rain falls faster than that, water collects at the lowest points it can reach: stairwells, window wells, and basement doors. That is why below-grade apartments are especially exposed.
The two floods behave differently, but the design question is the same. Where does the water go, and what is in its way? Architects can answer that in three places: the section, the site, and the materials.
The section: put sensitive equipment up high
In many older New York houses, the cellar holds the boiler, the electrical service, and the water heater. For generations that made sense, since it kept the equipment out of sight and out of the way. In a flood, it puts the most expensive systems in the most exposed place.
Flood-resilient design reverses this. The lowest level becomes the part of the building that can safely get wet, such as storage, parking, or an entry. Critical equipment moves up. There is a sustainability benefit too. A fuel-oil or gas boiler typically sits in the cellar, while heat pumps can often go on a roof or a raised platform. Making that swap can cut emissions and take a key system out of the flood path at the same time.
The site: keep rain where it lands
Every roof and paved yard sends water toward the sewer. Since 2022, the city's Unified Stormwater Rule has required new and redeveloped properties to manage more stormwater on site, and the city expects it to cut combined sewer overflows by about 360 million gallons a year by 2030.
The city is applying the same idea across whole neighborhoods. At NYCHA's South Jamaica Houses, a basketball court was designed to fill with water during extreme rain. It was the first project finished under the Cloudburst Management Program, in 2025. In 2026, the city announced a $95 million cloudburst project in Homecrest, Brooklyn, using porous pavement and underground storage to manage about 30 million gallons a year.
A single building has smaller tools, but the logic holds: green roofs that slow runoff, permeable paving, planted areas that absorb water, detention tanks that release it gradually, and rainwater harvesting, which we cover in water conservation in urban buildings.
The materials: build for a wet day
One of the quieter costs of a flood is what gets thrown away afterward. Drywall, fiberglass insulation, carpet, and particleboard cabinets absorb water, can grow mold, and usually end up in a landfill. Rebuilding them brings a new round of embodied carbon, and in areas that flood repeatedly, the cycle repeats.
Below the flood line, materials that can get wet, dry out, and stay in place work better: concrete, masonry, ceramic tile, closed-cell insulation, and cement board instead of drywall. In a flood-prone area, the most sustainable wall is often the one that never has to be rebuilt.
Decisions made at the drawing board
What sits at the bottom of the building, where the rain goes, and what the walls are made of all get settled long before there is a forecast. Resilience and sustainability are often treated as separate goals, but here they are mostly the same set of choices. For more on how they overlap, see our posts on sustainable disaster-resilient design and designing buildings to withstand climate change.
One of the quieter costs of a flood is what gets thrown away afterward.