What is the area of strength of a flat roof?

• A. the perimeter of the building
• B. Interior walls
• C. Center of the building
• D. Roof deck area

Answer: (A)

In a flat-roof building, the main load path for the roof is through the boundary: the exterior bearing walls around the edge. Those walls carry the roof’s weight down to the foundation, so that edge area is where the structure “shows its strength.” Interior walls are often non-load-bearing or carry only lightweight partitions, and the center of the building lacks continuous support unless there are internal beams or joists designed for that purpose. The roof deck area describes the surface itself, not a structural strength path, so it doesn’t define how the roof resists loads. Because the primary resistive forces come from the perimeter walls, the area of strength is the perimeter of the building.