Why do ceiling joists need to be securely tied together when spliced over a central bearing wall?

The requirement for ceiling joists to be securely tied together when spliced over a central bearing wall is fundamentally tied to their role in structural integrity and load distribution. Ceiling joists serve an important function in preventing the rafter system and the tops of walls from being pushed outward. This outward movement can occur due to the weight of live loads on the roof, such as snow, rain, or even the weight of roofing materials.

When ceiling joists are properly tied together, they help create a taut connection that resists the lateral forces exerted by the rafters. This is crucial in maintaining the structural stability of the building, as it allows the joists to effectively transfer any lateral loads back to the central bearing wall. If the joists are not securely connected, there is a risk that the rafters could spread, leading to potential structural failure or issues with the overall integrity of the roof system.

In summary, by preventing the movement of rafters and maintaining the proper alignment of the tops of walls, the ceiling joists contribute significantly to the building's resistance against the adverse effects of live loads. This is why securing ceiling joists together is essential in construction practices.