The most popular window in the U.S., and the most appropriate type for traditional house styles, it has two sashes that slide up and down. (On single-hungs, only the lower sash moves.) The screen mounts on the outside. When open, the sashes cover at least half the window opening.
Its hinged sash swings out like a door, so air can flow freely through the entire opening. Seals tightly to its jamb, making it one of the best types for keeping out the weather. Operates by hand or by turning a crank. When open, the sash is vulnerable to wind and rain. Best for contemporary and Prairie-style homes. The screen mounts on the inside.
Like a double-hung window on its side, the sashes slide on horizontal tracks—so there's no lifting—and the sashes always cover at least half the window opening. Best for contemporary house designs. Screens mount to the outside. The lower tracks require regular cleaning.
Keep the look of your home consistent with Tom Silva’s how-to for installing a sliding glass door and an expert’s advice for matching replacements windows to your historic home.
Awning (or Hopper)
It's like a casement mounted on its side. An awning window (shown) is hinged at the top and swings out, so you can leave it open when it rains. The screen is on the inside. A hopper window has bottom hinges and swings in. The screen is on the outside. Both types seal well, and with the right muntin configuration they can look good on either traditional or modern houses.
Common in Europe, this window has special hardware that allows it to tilt in like a hopper or pivot in like a door, depending on which way you turn the handle. The screen mounts outside. It does a superb job of sealing out the weather, but it's the most expensive window type.
Without a sash to open, it only lets in light, so it's less expensive and more energy efficient than comparable windows with sashes. Best for inaccessible areas, such as gable peaks, or as architectural accents; it can be crafted into almost any size or shape.