Which term describes the member that serves as the ceiling joist?

The member that serves as the ceiling joist is referred to as the Bottom Chord. This component plays a crucial role in the structural integrity of a roof system, as it supports the ceiling below and often ties the walls together, preventing them from spreading apart. The Bottom Chord connects to the vertical members, helping distribute loads and providing stability to the entire assembly.

Understanding the functions of the various roof components is essential. The Top Chord is the uppermost member of a truss and generally supports the roof load, while a Rafter is a sloping beam that supports the roof covering and transfers loads down to the walls or ceiling. A Purlin serves a different purpose by providing horizontal support for the roofing material between the rafters, but it does not function as a ceiling joist. Thus, the Bottom Chord is the correct term for the member that acts as the ceiling joist in a truss system.