Portions of buildings become airborne at high speed. Exterior wall materials on the windward sides often are thrown into building interiors. Missiles move much faster horizontally than vertically. Also, many more missiles move horizontally. Therefore, it is more serious to have a wall missing than a roof insofar as protection from missiles is concerned.
Missiles are a major threat to life.
Fortunately, they usually are stopped by substantial, somewhat massive interior partitions. Buildings without such interior partitions can be death traps. Chimneys collapse frequently, spilling their massive debris onto the roofs of adjacent spaces. Higher portions of buildings may collapse onto adjacent lower spaces, adding extreme loads to already weakened roof systems. The atmospheric pressure inside a building exceeds the outside pressure, causing the building to tend to explode .