Abstract: A method and apparatus is provided for maintaining functionality of at least one sliding panel of a sliding unit when a building structure to which the device is attached is subject to upward or downward movement. The method includes attaching a fixed guiding portion to the building and locating a variable panel track inside the fixed guiding portion, the variable panel track allowing a specified range of vertical movement of the sliding unit inside the fixed guiding portion in order to compensate for vertical movement of the building structure such that the at least one sliding panel is retained within the fixed guiding portion during the specified range of vertical movement, where either the fixed guiding portion is a fixed header and the variable panel track is a variable header track or the fixed guiding portion is a fixed floor channel and the variable panel track is a variable floor track.