On first glance, a window looks like a pretty simple piece of equipment. It has a frame, glass...some basic hardware. But if you look a little closer, you'll find there's much more than first meets the eye. A window must be designed to allow light and views-and in some cases, ventilation-- yet 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, has movable upper and lower sash that slide in tracks in the side jambs. A variety of specially-milled pieces make up the jambs, frame, casing and sash.

Some windows have real divided lites; others have snap-in wood grills 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 to buy and easier to clean than real divided-lite windows because they're actually a single sheet of glass.

The type of glass in a window has a great deal to do with how the window performs. Also see our full discussion of glazing.

A nail-on metal window, shown below 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.

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