by Don Vandervort, © HomeTips
A window isn’t just meant to bring in light and views to a room. It may also define a room’s shape, provide an architectural focal point, allow for ventilation, or provide for emergency escape. To serve such widely varying functions, windows are made in a vast array of types and sizes, each of which performs differently.
Broadly speaking, windows are either fixed or operable. Fixed windows are used mostly for accents or where light and views but not ventilation are important. Most round-top, triangular, and other unusually shaped windows are fixed, as are large picture windows.
Operable windows may slide up, down, or sideways, or they may hinge outward or inward. The windows shown at right represent the major types.
Contemporary windows are available in a number of innovative styles. You can buy a bent-glass corner window, curved-glass windows, or casements with no center stile, for example. Some beautiful bow and bay windows, which combine fixed and operable units, are also common.
A double-hung window, classic in appearance, offers excellent ventilation control. You can raise the lower sash or lower the upper one. (A single-hung window is similar, but only the lower sash opens.)
A casement window is hinged on one side and swings out when you turn a crank (some are inward swinging). Because it opens fully, it affords good ventilation and is easy to clean.
A slider offers a contemporary appearance. It’s made from two separate sashes: one is fixed and the other slides in a track. Half the window opens for ventilation. A slider is easy to operate, and most types are particularly weathertight.
An awning window hinges at the top and tilts out at the bottom, providing partial ventilation. These are often used above doors or other windows.
Jalousie, or “louvered,” windows are excellent for ventilation but are poor insulators. They leak a great deal of air.
A hopper window hinges at the bottom. It is normally used for ventilation above a door or window, where protected by eaves.
The tilt-turn is a reasonably new type of window. It tilts out for ventilation, but it also can be opened fully for cleaning or to serve as an emergency escape.
Round-top and other geometrically shaped windows are used as architectural accents.
A bow window is made from several windows positioned side-by-side to create an arching form. Similar to a bay window, it adds drama to a room.
A seamless bent-glass corner window is a fairly new product that offers unobstructed views at the corner of a house.
A bay window, made from a central sash and two angled side sashes, is a classic favorite for expanding a room with light, views, and drama. Angled side windows are often operable casements or double-hung windows.
Glass block is a light-allowing alternative to conventional windows, used both in exterior and interior walls. Various patterns allow varying degrees of light or privacy. Typical sizes are 6-, 8- and 12-inch squares and 4-by-8 and 6-by-8 rectangles made for 4-inch-thick walls.
Anatomy of a Window
On first glance, a window looks like a pretty simple piece of equipment. It has a frame, glass, and some basic hardware. But if you look a little closer, you’ll find there’s much more than first meets the eye.
In addition to allowing in light, views, and in some cases ventilation, a window must seal out the weather. It must shed heavy rain without leaking and block powerful winds. And if it’s operable it must open and close easily. To handle these tasks effectively, it has many parts and a surprisingly complex construction.
A double-hung wood window (shown at right), for instance, has movable upper and lower sashes that slide in tracks in the side jambs. A variety of specially milled pieces make up the jambs, frame, casing, and sash.
Window frames and sashes are built from wood, aluminum, vinyl, or a combination of these materials. Of these, wood is the best insulator and tends to yield the nicest appearance indoors. Vinyl and aluminum are more durable and maintenance-free, so some manufacturers apply a cladding of these materials to wood windows.
Some windows have real divided lites; others have snap-in wood grilles that imitate the look of divided lites. Though snap-in grills don’t look as substantial as real muntins, windows with these are less expensive and easier to clean than real divided-lite windows because they’re actually a single sheet of glass.
A nail-on metal window (shown at left), has many of the same parts and pieces as a wood window, only some of them are formed as single parts. The flange around the perimeter is made to nail on to the exterior wall sheathing for easy mounting during construction.
Natural light, views, a visual connection with the outdoors—glass makes possible many of the best features of houses. But as the amount of glass used in a house increases, energy efficiency usually decreases simply because glass windows and doors are not as effective as walls at insulating. For that reason, a great deal of research has taken place in recent years to improve the efficiency of glazings.
Now, when you buy or replace a window or glazed door, you can choose from a variety of glazings. Generally speaking, the more energy-efficient the glazing, the more expensive it is.
Heat loss through glass is typically measured by an R-value—the higher the R-value, the more efficient the glass.
U-value measures the amount of heat that can escape per hour through a given window. Two U-values are typical—one for the glass and one for the entire window, including the frame. The lower the U-value, the more energy-efficient the window is.
Though single glazing (a single sheet of glass) was once the standard, dual glazing or insulating glass is now more common for quality windows. This type of glass consists of two panes of glass separated by a thin air space. Though a single-glazed window offers an insulating value of about R-1, a dual-glazed model provides twice the value at R-2. You can also buy even more effective triple glazing with dual air spaces.
Low-e window glazing is perhaps the most common type of high-performance glazing. This employs an imperceptibly thin metallic film or coating between two glass panes that selectively rejects some energy wavelengths, greatly reducing heat transfer through the glass and minimizing the fading of furniture and carpets that can be caused by UV rays.
Argon gas–filled windows are even more energy efficient. When a window is injected with this natural, colorless, non-toxic gas, its insulating qualities are doubled. New “super” windows employ two low-e coatings to achieve incredibly high R-8 values.
Where ultraviolet fading is a real problem, such as in especially sunny climates, a solar-bronze- or solar-gray-tinted glass can reject unwanted heat and UV rays. Glass may also be purchased with a polymer coating that repels dirt, minimizing the need for window washing.
Some windows are sold with integral shades. You can even buy dual-glazed windows that have louvered mini-blinds between the glass panes. As an option in most cases, nearly all operable windows are sold with screens.
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