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You’re likely familiar with the different window operability types, and you may have even specified or installed them all at some point in your career – but do your customers know what they are and how they differ?

Because single- and double-hung windows are the most common types of windows, your customers might not know what they don’t know, and only think to select those types.

While there are many factors that must be considered before selecting window types for a home or building – including style, size, daylighting, budget, code requirements, placement, air leakage/energy efficiency, and more – this quick refresher on main window operability types is intended to provide information you can pass on to your customers to demonstrate their many options.

And don’t forget that, as with anything, product quality and long-term performance can vary – and that’s why choosing a product certified by reputable programs such as the WDMA Hallmark Certification Program is critical to ensuring quality, durability and performance, regardless of manufacturer.

Single and Double Hung

In single-hung windows, only the bottom sash is moveable vertically, whereas both sashes slide vertically in double-hung versions. Both options provide efficient ventilation to help cool the home or provide fresh air when it is desired otherwise. And of course, sashes that tilt in make cleaning the outside of the window much easier.

Single- and double-hung windows can have higher air leakage rates than other types of windows with projecting or hinged sashes, although they are still highly energy-efficient when designed to meet minimum energy codes or to qualify as an ENERGY STAR product.

These window types don’t take up exterior or interior space like hinged window do, making them a good choice in areas looking onto outdoor spaces like patios or walkways, or onto tall shrubbery. Double-hung windows are also good choices for single and multifamily residential construction where pets or small children can be common, as the top can be lowered for ventilation while the bottom stays securely closed.

Single Hung Marvin


Casement windows open out, pivoting from side hinges. Hinged windows like casements offer lower air leakage rates than sliding windows because the sash closes tightly in the frame. When closed and locked, casement windows offer an effective seal for improved energy performance.

Casement windows are typically operated by a crank mechanism, though there are push-out styles operated by a hinged lever. The hand crank or lever makes them easier to open than sliding windows which also makes them ideal in scenarios where reach may be restricted or physical ability is limited.  Because the sash protrudes from the plane of the wall, it can be controlled to catch passing breezes for better ventilation, but screens must be placed on the interior side.

Like awning windows, which open outward, casements should not open out into a walkway or outdoor area, as they can be an obstruction. In-swing casement windows are available for these scenarios, although the trade-off there is that they take up space inside the home rather than outside.


Like casement windows, awning windows open outward but are hinged at the top of the window sash, and are also generally operated by a crank, though push-out awning windows that are operated by a hinged lever are also an option.

Awnings can be placed above, below or alongside other windows, or over doors, for extra ventilation and light.

Also like casement windows, awning windows generally have lower air leakage rates because they close the sash tightly. Screens are placed on the interior of the window unit.

Awning windows are ideal for providing ventilation in rainy climates because they keep the rain out while letting fresh air in, or they can be placed high on a wall in a clerestory design to allow light in while maintaining privacy and still providing fresh air ventilation.



A hopper window is hinged on the bottom frame of the sash and opens inward from the top, not the bottom – the opposite of an awning. They are operated by a single handle and, like other hinged windows, generally offer lower air leakage rates because the sash closes by pressing against the frame, providing a tight seal. The entire window area can also be opened.

They work well when home- or building owners want an operable window for light and ventilation, but don’t have a lot of room in a wall and are a good choice for basements.

Horizontal sliders 

These windows open with the sash sliding horizontally left or right on tracks at the top and bottom of the sash. Like single- and double-hung windows, one or both sashes can be operable.

Because they slide open without protruding like single and double-hung windows, horizontal sliders are a natural fit for rooms facing walkways, porches or patios. They work well in contemporary-style homes, and as with single- and double hung windows, they are also popular for satisfying bedroom emergency escape requirements.

Marvin Slider Window
Tilt Turn Marvin

Tilt and turn

Tilt-and-turn windows are a hybrid between casements and hoppers. The sash swings inward from a side hinge when operated as a casement window, and opens from the top when operated as a hopper window. They are controlled by a single handle that serves for both operation options.

These windows offer operational and design flexibility, depending on whether they are used as casement (allowing the sash to open wide for maximum airflow,) or used as a hopper (which provides a smaller amount of ventilation, but more security).

Skylights/roof windows

Most skylights are installed to provide daylight but can also provide effective ventilation. As skylight technology has evolved, daytime heat gain and nighttime heat loss are better mitigated with recent developments in design, including automated opening and closing, and automated shades and blinds.

Ventilating skylights are becoming more common and usually open outward at the bottom, while some units vent through a small hinged panel.

Manually operated venting skylights are opened with a pole, chain or crank.  Automated skylights with electric motors or pneumatic devices are also available, and some models even incorporate moisture sensors, so the skylight automatically closes when it rains. Depending on their location, larger skylights are sometimes called “roof windows,” and can also be used for emergency escape, provided they meet all building code requirements for emergency escape and rescue, including height from the floor and opening size.


By: Jeff Inks

Senior Vice President of Advocacy for the Window & Door Manufacturers Association.

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