Why are roofs generally not as strong as floors?

Roofs are generally designed to support lighter live loads compared to floors. This design consideration arises from the different functions these structures provide. Floors need to support not only the weight of people and furniture but also moving loads, such as those from furniture being moved or equipment being transferred. As a result, floors are constructed with a greater emphasis on load-bearing capacity.

In contrast, roofs typically support much lighter loads, mainly including the weight of roofing materials, insulation, and occasional maintenance personnel. Additionally, roofs are engineered to handle snow or rain loads, but these are often temporary conditions and considered in the overall load calculations. Therefore, the lighter design requirements for roofs lead to them being less robust compared to floors, which are built to endure heavier and more variable loads.