Ceiling joists are primarily described as:

Ceiling joists play a crucial role in the structural integrity of a building, and the correct description emphasizes that these members are horizontal structures used in conjunction with rafters and sometimes roof joists. This relationship is important because ceiling joists are typically installed parallel to the rafters, providing a framework that helps support the ceiling below and contributes to the overall stability of the roof assembly.

By connecting the rafters across the span of the room, ceiling joists facilitate even load distribution and prevent the rafters from spreading apart due to forces such as wind or snow. This interaction between ceiling joists and rafters contributes significantly to maintaining the strength and durability of the roof.

Understanding the function of ceiling joists in conjunction with rafters highlights their role beyond just horizontal support, as they also actively engage in the structural dynamics of the entire roofing system. This balance ensures that the loads above, such as snow or roof material, are adequately supported, which is that much more vital in ensuring the safety and longevity of the building.