What is required on rafters that do not support a ceiling and are spaced 16 inches on center?

In situations where rafters do not support a ceiling and are spaced 16 inches on center, the incorporation of collar ties is essential for enhancing structural integrity. Collar ties are horizontal members that are installed between opposing pairs of rafters, typically in the upper third of the roof's vertical span. They serve several critical functions:

1. Stability: Collar ties help resist the outward lateral thrust exerted by the rafters, preventing them from spreading apart under load, which can be particularly important in steeper roof configurations.

2. Load Distribution: By connecting the rafters, collar ties allow for a more even distribution of loads, which helps maintain the alignment and structural performance of the roof.

3. Preventing Roof Failure: In the absence of ceiling joists, the roof may be more susceptible to lateral forces such as wind. Collar ties brace the rafters, providing additional support against such external influences.

While blocking is also a means of improving stability, it typically refers to short pieces of lumber inserted between rafters to provide support for sheathing or to control lateral movement, but it does not serve the same purpose as collar ties in resisting the thrusts created by the roof structure. Ridge beams and king posts are more