Collar ties function to prevent what issue in roof framing?

Collar ties are horizontal members installed in roof framing, specifically connecting opposite rafters near the ridge of the roof. Their primary function is to prevent the rafters from separating or pushing apart under the weight they are bearing. In particular, they are effective in controlling the tension between the rafters, which helps maintain the structural integrity of the roof.

By anchoring the rafters together, collar ties help resist the outward forces that occur during structural loading, such as when the roof supports snow accumulation or during high wind events. Without collar ties, the rafters could move apart, leading to a loss of proper alignment and potentially causing serious structural issues, including roof failure.

While roof sagging can occur due to various reasons, collar ties specifically address rafter separation, which can contribute to sagging if left unmitigated. Therefore, collar ties primarily focus on preventing the rafter separation from the ridge rather than addressing issues like over-installation or direct damage from snow loads.