Flooding can come in many forms.

Perhaps the balcony over your front door is not properly constructed and is not properly shedding rain, so one day during a torrential thunderstorm you suddenly have a flood coming in OVER your front door.

Perhaps your water heater pan is not draining correctly, and one day you have a catastrophic containment failure in your water heater, causing an interior flood.

Perhaps you change the toilet in an upstairs bathroom, and the new modern toilet is not providing enough water per flush to make the long run of the upstairs plumbing. So, it clogs up over time, then one day it backs up while you’re taking a shower, and you’re standing in multiple inches of grey water. Then the water does slowly drain, but you don’t notice that the pipe has cracked above the clog and it’s actually flooding into the room below, through the light fixture.

Perhaps the main schedule 40 PVC pipe from the water main at the street slowly develops a crack, due to the roots of a tree nearby, and one day you discover that the water pressure in your house is really low and that you have flooded the whole street.

Guess which of these have happened to us?

All of them?

Correct in one!

Mine were incorrect drainage outside, causing water to pool high enough inthe back yard that it came through the slider into the converted garage, soaking the pad and carpet there (in a few different locations actually), and the much worse one where a room was build off the same garage onto a concrete pad that was laid, but one of the walls was build on top of a covered deck that was build off the garage on one side, which had water run down it, hid the deck, then immediately go under the wall to the concrete pad meaning even moderate rains that didn't result in outside flooding would result in that room's pad and carpet getting wet and needing to be entirely removed, and the wall ripped out and rebuilt as it eventually was overtaken by mold. A large chunk of the house needed to be blocked off, industrial fans installed to dry it out, and then professionally redone.

Building codes exist for reasons. Sometimes they seem frivolous, but often they're there for a damn good reason.