Double hung and sliding windows are similar because both have sashes (panels) that slide or glide as opposed to opening in or out, like casement or awning windows.
There are actually two variations of hung windows—double-hung and single-hung—although they are both commonly referred to as double hung.
The only real difference between the two is that single-hung windows have one movable sash (at the bottom), while double-hung windows have two, creating more options for ventilation, but also making the window less energy efficient because there is no fixed sash. Single-hung windows are also typically less expensive.
Hung windows became popular in the 17th century with the invention of the sash, and are still relatively popular today, especially for more traditionally-designed homes.
Since they don’t open in or out like casement and awning windows, these windows are also a good choice for confined areas or where the window opening is beside a walkway, deck, or patio. A further advantage over casements is that they aren’t subject to distorting under their own weight when opened.
Sliding windows, both single and double-sliders, are essentially a hung window turned sideways. Sliders are most commonly used for window openings that are much wider than they are tall, typically basement windows.
Aside from being options for those specific applications, the major advantages of sliding windows are:
- They are generally the least expensive style of opening window since they do not require sophisticated opening/closing hardware.
- They are, in most cases, the best choice for egress windows in smaller window openings, especially in basements.
However, sliding windows have lost a great deal of their appeal because of these disadvantages:
- They close with a friction fit across the weatherstripping, unlike casements and awnings that close with a compression fit. As a result, weatherstripping wears out faster, leading to a greater chance of air and water penetration.
- Whereas casement and hung windows can blend with a number of design styles, both contemporary and traditional, sliders are less appealing aesthetically, and are chosen most often for their lower cost and suitability as egress windows.