Single and double hung sash windows
Traditional sash windows were single hung, with the lower section moving up and down using a system of weights and pulleys concealed in the frame. This simple mechanism gives the window its smooth movement and balanced operation.
The more modern double hung sash allows both sashes to move independently, giving better control over ventilation. The upper sash can be lowered to let warm air out, while the lower sash can be raised to bring in fresh air. Many newer models also tilt inwards, making cleaning easier from inside the home.

