Hurricane Harvey

[Fireball]

What, like this?




YES.





People underestimate the power of water.

Think of it this way: If you're inside a car that's surrounded by water up to the windows while the interior of the car is (relatively) dry, you'll have a hell of a time pushing the door open to escape because of the pressure differential between the interior and exterior of the car door.  BUT if you allow the car interior to flood, you equalize the pressure on both sides of the door and you'll be able to open the door to get out.  And that's not even talking about whether the car has been physically picked up by the floodwaters and washed away while you're trying to escape.

A house completely sealed off from flood water intrusion would have a similar principle going on: completely sealing it off from water intrusion means the pressure exerted by the water outside can build up until the structural components holding the house to its foundation fail and the house can be washed away.  If water is allowed in it can reduce the pressure on those structural components and reduce the risk of the house being completely lost.  The pressures we're talking about, though, have a lot to do with how strong a current there is and that can vary.  Houses nearer to rivers, creeks, aquaducts, spillways and the like are at a higher risk than those further away where the currents would be weaker.


Remember, though, that dams are specifically engineered to resist the hydrostatic pressure of the water they are holding in their reservoirs.  Houses aren't built like that.  Houses are engineered with static loads in mind and where dynamic loads are considered it's usually wind and earthquakes that drive the design load, not water.  I have never heard of a developer who built a neighborhood where they engineered all the houses to resist being torn from their foundations by floodwaters.


It's a thing, but retrofitting a house to be flood-proof is difficult and expensive.  It's much easier to board up a house to prevent wind/debris damage than it is to prevent 3+ feet of water flooding you out.

Large wooden sailing ships were able to withstand the stresses of storms at sea without too many ill effects so why can't houses in known flood areas withstand flood waters? Maybe it's because no one has ever built houses with that problem in mind?

Wooden ships are shells of wood and have their gaps filled with caulking, usually tar, and the wood is pushed together by the water pressure, which helps the tar seal them. Wood framing of a house where the studs are typically 16 inches on center isn't even close to a near-continuous wall of wood like would be in a wooden ship's hull. A residential house is quite far from a ship, in terms of construction.