The Standard Flood Insurance Policy (SFIP) definition of a basement is any area of the building, including any sunken room or sunken portion of a room, having its floor below ground level on all sides.

It doesn’t matter what anybody living or working there does with it or calls it—if the floor is below ground level on all sides, then the area meets the definition of a basement.

When there is a flood, where will floodwater go first? That’s right; gravity makes sure that the water seeks the lowest level and goes to the basement first.