What’s the difference between single and double hung windows?

Double hung windows are based on the iconic design of single hung windows, there is however one major difference, the number of operable sashes. A single hung window has one fixed/non-operable sash and one operable or moveable sash, whereas double hung windows have two operable or moveable sashes. Single hung windows offer better energy efficiency and security than double hung windows as the top sash is stationary and will not loosen over time.