What is a common feature of light-frame buildings in relation to collapse potential?

The statement that additional collapse is unlikely with fewer than three floors is based on the structural characteristics of light-frame buildings. Typically, these structures are designed with a focus on lightweight materials and components, which help to reduce the overall mass of the building. When such a building has fewer than three floors, its overall height and mass are less conducive to progressive collapse.

In light-frame construction, the risk of progressive collapse increases with greater height and the complexity of the system due to loads and potential failure mechanisms. Buildings with fewer than three floors often have simpler structural systems, and because of that, they may experience less severe consequences from localized damage. This means that while there still may be failure in certain parts of the building, it is less likely to lead to a overall collapse of the structure.

In contrast, taller structures or those with more floors can accumulate more loads and stress factors that can adversely affect their stability, increasing the risk of complete structural failure in the event of damage. Thus, the common understanding among structural engineers indicates that light-frame buildings typically have a lower collapse potential when they are limited to fewer floors.