Which type of window can be opened either up or down?

The double hung window is designed with two operable sashes, which can slide vertically within the frame. This allows for both the upper and lower sashes to be opened independently, enabling airflow from either direction—top or bottom. This versatility makes double hung windows a popular choice in residential applications, as they provide options for ventilation depending on the weather or personal preference.

In contrast, a single hung window features only one operable sash, typically the lower one, which can be opened upward, while the upper sash remains fixed. Sliding windows operate by moving horizontally and do not allow for vertical adjustments. Casement windows are hinged and open outward, typically by turning a handle, making them less versatile in the manner of opening compared to double hung windows. The functionality of the double hung design is what makes it uniquely able to open both up or down.