Sliding glass door

In architecture and construction, a sliding glass door (also patio door or doorwall) is a type of sliding door made predominantly from glass, that is situated in an external wall to provide egress and light. The doors can give access to a backyard or patio while providing a pleasant view, and when not fully covered can be a source of passive daylighting. Like a window, when open it also provides fresh air and copious natural light. It is considered a single unit consisting of two or more panel sections, some or all being mobile to slide open. Another design, a wall-sized glass pocket door has one or more panels movable and sliding into wall pockets, completely disappearing for a 'wide open' indoor-outdoor room experience. The sliding glass door was introduced as a significant element of pre-war International style architecture in Europe and North America. Their predecessor is the sliding Shōji and Fusuma panel door in traditional Japanese architecture. The post-war building boom in modernist and Mid-century modern styles, and on to suburban ranch-style tract houses, multi-unit housing, and hotel-motel chains has made them a standard element in residential and hospitality building construction in many regions and countries. "Handedness" of a sliding door is expressed as seen by an observer outside the building. When standing outside, a left-handed door opens from left to right (when closed, the handle is on the far left), and a right-handed door opens from right to left (when closed, the handle is on the far right). These relationships are sometimes described with the letters O and X, where O is the fixed panel and X is the sliding panel. The O/X notation allows the description of doors with more than two panels. The traditional sliding doors design has two-panel sections, one fixed-stationary and one mobile to slide open. The actual sliding door is a movable rectangular framed sheet of window glass that is mounted parallel to a similar and often fixed similarly framed neighboring glass partition.