The land is full, there are no roads, and cars can fly. Some spend their whole lives in a single square mile. Life isn't entirely miserable for the average person, but trust me. You wouldn't choose that life. The rich have houses, but even they have to live cheek to jowl with their neighbours.
So floating houses have been built. Each house has a section above water on which to land a car, enjoy the sun etc., but most of the house is below sea level for stability. There's a lot of rising and falling, but you get sea legs eventually.
There's one problem, when there's a storm the house becomes dangerous. Throwing its occupants around violently. To combat this the designers make the houses submersible.
The question is: How far must the house submerge to avoid the storm? Such that the occupant could carry on moving around in the house without being tossed about? EDIT removed extra questions.