
The bottom rail is the lowest horizontal member of a window sash, forming the base that supports the glass and often incorporates a sash lift for ease of operation. In timber sash windows, it’s typically thicker than other rails to add weight and stability, helping the sash glide smoothly within the frame.
During restoration, maintaining the correct profile and weight of the bottom rail is crucial-especially when upgrading to double glazing-to ensure proper balance with the counterweight system.


