What Are Casement Windows? | The Hinged Window Explained

A casement window is a window with a sash hinged at the side that swings outward like a door, typically operated by a crank.

If you’ve ever turned a small crank handle to push a window open, you’ve used a casement window. These are the windows that attach to their frames with hinges on one side, so the entire sash swings outward to catch a breeze. They stand apart from sliding windows, which move horizontally in tracks, and from double-hung windows, which move vertically. Casement windows are a staple in American homes because they offer strong ventilation and a tight seal when closed.

How Does a Casement Window Work?

Casement windows operate through a simple but effective mechanical system. A crank handle on the interior connects to gears or an operating arm. When you turn the crank, the arm pushes the sash outward on its side hinges, opening the window like a door. Turning the crank in the opposite direction pulls the sash back into the frame, where it locks tightly against a weather seal.

That side-hinged design is the defining feature. The hinge placement determines the opening direction—some casements hinge on the left, others on the right. When closed, the sash presses firmly against the frame, which is why these windows are often praised for energy efficiency.

What To Know Before Buying Casement Windows

Before you purchase, a few details matter. First, because the sash swings outward, casements need exterior clearance. Shrubs, walkways, screens, or nearby structures can block the window from opening fully. Second, an open casement acts like a sail—strong winds can strain the mechanism or make the window difficult to control. And third, if you’re using a casement as an emergency egress opening, the clear opening matters more than the nominal window size.

That calculation accounts for the hardware and frame, so you know the actual space available. This spec varies by manufacturer and series, so always check the technical sheet before ordering.

Are Casement Windows Energy Efficient?

Yes, casement windows are generally considered energy-efficient, but the reason is mechanical. When you close a casement, the crank pulls the sash tight against the frame, compressing the weatherstripping. That compression creates a strong seal that blocks drafts and air leakage, which is a key factor in a window’s overall efficiency.

The glass and frame materials also play a role. Double-pane glass with low-E coatings, argon gas fills, and insulated frames all improve thermal performance. If energy efficiency is your priority, look for casements with those features rather than relying on the operating style alone.

While the seal is a strength, the exterior swing is the trade-off. In some climates, an outward-opening window can be more exposed to wind and weather damage when left open. Properly closed and locked, though, a casement’s seal is often better than that of sliders or hung windows.

Andersen’s 400 Series casement specs are a good reference point for sizing, but other manufacturers—including Pella, Jeld-Wen, and Marvin—offer their own casement lines with different dimensions. Andersen’s product families include the A-Series, E-Series, 400 Series, 200 Series, and 100 Series, each with different price points and performance levels.

Casement vs. Awning: What’s the Difference?

The terms get confused in casual conversation, so here’s the clean breakdown. A casement window is side-hinged—the sash swings left or right. An awning window is top-hinged—the sash swings outward from the bottom, so it opens like an awning over a shopfront. In U.S. retail terminology, these are distinct products. Some technical sources use “casement” broadly for any hinged opening, but American manufacturers and consumers apply it specifically to side-hung units.

For basement spaces, casements are a popular choice because they open wide for ventilation without taking up floor space. If you’re shopping for a basement installation, our roundup of the best basement casement windows covers tested models with real specs to help you compare.