What type of window has two sashes that move past each other in a vertical plane?

A double hung window features two sashes, meaning both the upper and lower sections can move up and down within the frame, allowing for ventilation from both the top and bottom. This design not only provides flexibility in airflow control but also makes it easier to clean the exterior of the window from inside the building, as both sashes can be tilted inward. The ability to operate both sashes distinguishes it from other types of windows.

In contrast, a single hung window has a fixed upper sash and a lower sash that moves, which limits the options for ventilation. A casement window swings outward on hinges, providing a different style of opening compared to the vertical sliding motion of a double hung window. A slider window operates horizontally, with sashes that slide from side to side, also differing from the vertical operation of the double hung type.