Louisiana got besieged by a 500-year flood a couple weeks ago. I received a firsthand account from my cousin, who lives in Baton Rouge. He was one of the lucky ones – flood waters didn’t reach his house – and he has spent days helping neighbors clean out.
An unnamed, weeklong storm dropped more than 20 inches of rainwater over a third of the state. Rivers reached record flood stage, mixing with mud and sewage as the water submerged low-lying land. Outsiders tend to assume all of Louisiana is low-lying, but many affected houses are not officially in a floodway and many residents do not have flood insurance. Even for those who do, the federal provisions are messy and limited to $100,000 of personal property. In homes where the water has receded, the stench is almost unbearable. Cleanup involves removing personal items from the house, then gutting and replacing everything below the high-water line… and often, because of wicking moisture, well above that line too.
How can you design or retrofit a house to minimize the damage a flood would cause? LSU College of Agriculture developed this proposal, which divides walls horizontally in two. A chair rail hides a gap in the drywall and a partition between lower and upper insulation. Thus, any flood water that infiltrates the house can’t damage anything above the chair rail. The concept is to eliminate “water bridging”, much like a Passive House avoids thermal bridging to keep heat in.
To further protect the lower half of the house, LSU recommends water-resistant flooring and wall panels, along with insulation that doesn’t absorb water, such as rigid foam. Electrical wiring is as high as possible. None of the details seem overly expensive to install, other than requiring a like-minded contractor to do the work correctly. I’d recommend all homeowners in a floodway, and even outside of it (500-year floods do happen), to consider protecting their property with details like these.
Of course, you could also literally elevate your house, or surround your property with a cofferdam, or (if your house is on wheels) drive it to higher ground when heavy rain threatens. But most folks who take action at all will probably go for the LSU ideas.