Unlike casement or awning windows that crank out or sash windows that move up and down, sliding windows are built into a track system and operate horizontally instead of vertically. They are common in manufactured homes and in houses with walls that are too low to accommodate standard sash windows. The screens included in most sliding window installations also move horizontally, while others are permanently attached and are not movable.
Sliding windows, or gliding windows, offer more clear glass viewing area than other types of movable windows. They also provide an alternative when casement, or roll-out, windows would create an obstruction on walkways, porches, decks or patios. While older sliding windows were a chore to take apart for cleaning, today's windows can be easily lifted from the tracks for cleaning or maintenance. Other types swing out of their tracks to simplify cleaning and maintenance.
Sliding glass windows are constructed of vinyl or aluminum frames wrapped around a pane of standard glass or a polycarbonate, or polymer plastic, material that is lighter, easier to handle and is less likely to shatter than glass. Both glass and polycarbonate come in different thicknesses. Polycarbonate that is roughly 3/10 of an inch, or three miliimeters, is comparable to a single pane of standard glass. A polycarbonate pane measuring 9/10 of an inch corresponds to a pane of standard insulated glass, while a 2-inch-thick pane of polycarbonate is comparable to triple-pane standard glass.
Sliding windows are available in standard sizes or can be custom-built to suit all types of housing construction. Window styles vary from two to multiple sliding sections, also called lites, depending upon the building's design. In some cases, both sections of the window are movable, while in others, just one side is operable. Movable or stationary screens can be installed inside or outside the window unit.
Sliding windows present more of a challenge when it's time to seal windows and doors against colder weather. To be effective, weatherstripping materials should be installed inside the window track, which can interfere with its performance, an important factor to consider particularly in areas where winter temperatures fluctuate widely. According to the U.S. Department of Energy, sliding windows are considerably less energy efficient, allowing for a greater escape of heat than casement or other types of hinged windows that shut tightly against the frame.