What is the function of the sill in a window assembly?

The sill in a window assembly primarily acts as a barrier for water. This critical component is designed to direct water away from the window's interior to prevent moisture intrusion that can lead to damage or deterioration. The sill's sloped design helps shed water, ensuring that any rain or condensation that collects on the window is channeled toward the exterior.

While a sill does contribute somewhat to the holding of the window in place and providing some structural characteristics, its primary role in mitigating water issues is essential for the longevity and functionality of the window assembly. Furthermore, it is not considered part of the movable framework; rather, it is a fixed component integral to the overall window structure. This unique function underscores the importance of a well-designed sill in maintaining the integrity of window installations and enhances the importance of proper installation techniques and materials in protecting against water ingress.