Double- and single-hung windows are absolutely the most classic style of window you can have in your house. Want proof of that?
If you ask a child to draw a house, he or she will almost certainly draw a box with a gable roof and the window will look like a single- or double-hung window. Not a slider, a casement or a picture window.
Single- and double-hung windows are indeed the most iconic type of window, but how are they different and, between the two, which one should you buy?
How They Are the Same
Both single-hung and double-hung windows are vertical-sliding windows with an upper and lower sash. A sash is the square or rectangular frame containing the window glass and may include smaller pieces, called muntins, that divide the glass.
Single- and double-hung windows will look identical from a distance.
How They Are Different
The difference is that with single-hung only the bottom sash moves, while the top half is permanently fixed. With double-hung, both sashes slide up and down.
With fewer moving parts, single-hung windows conceivably are more weather resistant.
Double-Hung Window: Easier to Clean, More Airflow, Safer
The double-hung window is the most common style of window available today. And the reason is simple: double-hung windows are easier to clean.
Double-hung windows with tilt-in (also called tilt-out) design can be cleaned from inside the house. With single hung windows (and older double-hung windows without tilt-out function), it's difficult or impossible to clean the outside of the lower sash from indoors. You have to reach it from the outside--easy if the window is ground-level, difficult if the window is upper-level.
Single-hung windows can also have a tilt-in or removable lower sash, but you still have to reach outside the window to clean the upper sash, a perilous task.
The ability to open the upper sash on a double-hung window is another advantage in terms of airflow. Sometimes it's nice to open the upper sash and not have air blowing in from below. You can also create a minor recirculating effect by opening both sashes about halfway or less. In theory, this allows warmer air to escape through the upper sash and cooler air to enter through the lower sash. But in reality this natural convection has little cooling effect on a room.
Finally, for homes with small children, double-hung windows' top opening sash allows you to keep the lower sash closed, yet still have airflow coming though the open top.
Single-Hung Window: Simple, Weather Resistant
Single-hung windows predate double-hung and may be preferred for an authentic look on historic homes. In modern homes, single-hung windows additionally may be preferred because they cost a bit less than double-hung.
Also, it's often argued that single-hung are less susceptible to air infiltration, or leakage, simply because the upper sash is fixed and cannot develop looseness the same way a moving sash can. This won't be reflected in performance ratings, as both types of windows must meet the same standards. But in use, window seals tend to degrade over time, and a moving sash cannot be sealed with caulk like a fixed sash can.
If the upper sash of a single-hung window breaks, a glazier must come in and repair the window. With a double-hung window, though, the homeowner could replace the upper sash.
Which One to Buy?
When you're shopping at window showrooms, compare single- and double-hung models for looks and cost as well as ease-of-cleaning and other convenience factors.
If you'd like to be able to open both sashes, choose double-hung. If you'd like to be able to remove both sashes, again choose double-hung. Otherwise, you might be perfectly happy with single-hung and can save a few bucks to boot.
Generally, double-hung windows are now so common that it is easier to buy them than to buy single-hung windows--more choices, better prices.