Eighty percent of New Orleans remains underwater today, and rescue teams continue to collect survivors from the tops of their submerged homes. What will happen to these flooded houses—will their owners ever move back in?
It depends on the severity of the flooding. For homes that are completely underwater or that are flooded to the upper floors, the cost of repair will probably exceed the cost of moving. At the very least, the interior finishes of a waterlogged house must be stripped and replaced. High water can also damage the wiring, gas lines, furnace, and septic system, as well as furniture and appliances.
Wind and water can cause a house's structural components—the struts, studs, and foundation—to shift or warp. Tilting walls or a shifted roof also suggest dangerous structural damage that could signal an imminent collapse. Flood victims should check the foundations of their homes for cracks before venturing inside.
Inside the house, ceilings may sag under the weight of trapped water or soggy drywall. Wet floorboards bend and buckle, and the roof may leak or break altogether. Flooding in the basement can be especially dangerous; if the water is removed too quickly, pressure from the soaked earth outside can push inward and crack the foundation walls.
Brick and masonry houses will suffer less exterior damage than those made of wood. In all types of housing, though, flooding will most likely destroy the interior walls. Soaked wallboard becomes so weak that it must be replaced, as do most kinds of wall insulation. (The higher the water gets, the more interior walls must be replaced.) Studs will eventually dry out and return to their original shape, but any plywood in the walls is likely to swell and peel apart. Water can also dissolve the mortar in a chimney, which creates leaks and thus a risk of carbon monoxide poisoning once the heat comes back on.
Structural hazards account for only one category of water damage. Floods often deposit dirt and microorganisms throughout the house. Silt and sediment can create short circuits in the electrical system as gunk collects in walls and in the spaces behind each switch box and outlet. Appliances, furnaces, and lighting fixtures also fill with mud, making them dangerous to use.
Anything that gets soaked through with water may contain sewage contaminants or provide a substrate for mold. A long-lasting flood provides more time for the mold to grow and requires more cleanup after the fact. Carpets have to be thrown away, along with mattresses, bedding, and most upholstered furniture. Kitchen items, clothes, washing machines, and dryers must be disinfected with bleach, and all surviving interior surfaces should be cleaned to prevent mold growth. Standing water in a house can also serve as a breeding ground for insects and other animals.
Bonus Explainer: What about flooded cars? A car that has been completely submerged will be considered "totaled" by most insurance companies. But that doesn't mean you can't fix it up. Floodwater must be drained from the engine, transmission, brakes, and fuel system, and bits of mud must be cleaned out. Problems will also arise if too much water mixes with the oil, transmission fluid, brake fluid, or antifreeze. The small electronic parts under the hood and in the dashboard are especially susceptible to water damage. Controls for door locks, windows, and interior climate tend to be difficult to clean.
Explainer thanks Martin L. King of the Association of Specialists in Cleaning & Restoration.