Abstract: Single-hung, double-hung, horizontal sliding/gliding windows, and sliding door assemblies having a weathering block of the present invention are disclosed herein. The weathering block of the present invention is an integral component of a window or door frame, and functions to substantially seal leaks around movable joints, such as windows or doors. In an embodiment, the weathering block substantially prevents air and water infiltration around windows and doors by substantially eliminating gaps between the frames and moving parts when they are closed. In an embodiment, the weathering block includes a back surface sufficiently designed to engage a side jamb, a head jamb, or a sill plate of a window or door frame; a front surface sufficiently designed to maintain weather-stripping; a first side surface sufficiently designed to maintain weather-stripping; and a second side surface sufficiently designed to maintain weather-stripping.