What is the primary purpose of an isolated joint in construction?

The primary purpose of an isolated joint in construction is to minimize cracking and allow for movement of the slab. Isolated joints are specifically designed to accommodate the thermal expansion and contraction of concrete, which happens due to changes in temperature and moisture levels. When a concrete slab expands or contracts, an isolated joint provides a predetermined point for movement, thus preventing the development of tensile stresses that could lead to cracking. By doing so, these joints help maintain the structural integrity of the slab and extend its lifespan by minimizing potential damage from environmental factors.

In contrast, the other options serve different functions in construction. Adding strength to the structure generally involves the use of reinforcements or structural elements rather than isolated joints. Enhancing thermal insulation typically relates to materials and construction techniques focused on energy efficiency rather than the function of joints. Supporting vertical loads from the roof is about the structural framework and load-bearing elements, which is unrelated to the movement control that isolated joints provide.