Early to mid C18th nine over nine Georgian sash window with flush casements and woodern external shutters Micklegate York
Sash Window : A sash is a wooden frame (or any other material ) used to house glass for a window. A sash window is a double hung frame with the frame sliding up and down on a series of pulleys. Can be opened at top or bottom. Came into fashion in England in the Georgian Period.
Here is a potted history of the sash window by a sash window manufacturer
You can view all of my sash window photo's here
All things Georgian