What is the primary characteristic of a joist in construction?

The primary characteristic of a joist in construction is that it is a light beam designed to support a floor. Joists are typically horizontal structural members that span an open space, transferring loads from the flooring above to beams or walls that support them. This functionality is crucial in ensuring that floor systems can handle loads without excessive deflection or failure.

Joists often made of wood or steel, are crucial in residential and commercial construction because they provide the necessary support for the flooring system while minimizing material usage and weight. This attribute of being lightweight yet effective in load-bearing makes the joist distinct in construction, allowing for effective support across various building designs.

While other options describe elements of construction, they do not capture the specific function and application of a joist. For instance, beams that directly support roofs and connectors between walls serve different structural purposes that do not align with the core definition of a joist. The mention of thermal performance also pertains to insulation and energy efficiency considerations, rather than the specific role of a joist in structural support.