Which window type consists of an upper and a lower sash that slide vertically in the side jambs?

The window type that consists of both an upper and a lower sash that slide vertically within the side jambs is known as the double-hung window. This design allows for both the upper and lower sections to move independently, providing versatility in ventilation. Homeowners can open either sash to allow fresh air to flow in from the bottom while allowing warm air to escape from the top, which is particularly effective in managing airflow and maintaining comfortable indoor temperatures.

Additionally, the double-hung design is a traditional and popular choice due to its ease of cleaning and ability to fit into a variety of architectural styles. This contrasts with other window types mentioned, such as single-hung windows where only the lower sash is operable, and sliding windows that operate horizontally. Casement windows open outward and do not feature the vertical sliding mechanism found in double-hung designs.