Single Hung windows provide ventilation through the bottom “sash,” which is the only moveable part of this window. The top portion remains stationary. Single-hung windows are typically at a lower price and are great for energy efficiency and security.
Very little air can penetrate with good energy efficiency due to a fixed sash to the frame. With a single-hung window, you can also choose to have a tilt window which opens inwardly instead of simply moving upwards and downwards.
On a single hung window, the sash fits directly inside the frame and adds to improved integrity, strength, solar heat gain, air leakage, etc. This option provides a narrower profile where you get a little more glass. Your window is a little more secure with the wind due to the sash’s integration with the weather stripping.