Windows provide natural light and ventilation and are classified by the method by which they open and close (e.g. double-hung window). Windows are made from wood, steel, aluminum, vinyl, vinyl-clad wood or aluminum. Some modern windows have a thermal break, usually Bakelite, between the interior and exterior part of the window to prevent condensation during the winter months.

Components:

	Pane (or glazing): the plate of glass (usually 1/8 inch thick for single pane.)
	Sash: the portion of the window that slides or pivots when you open and close the window unit. The sash includes the glass, its supporting framework, locks and lifts.
	Rails: top and bottom part of the sash.
	Stiles: sides of the sash.
	Stops: hold the sashes in place when sliding or stops a closing window that pivots.
	Jamb: the side of the window frame.
	Sill: the bottom of the window frame.
	Head: the top of the window frame.
	Mullions: used to divide the pane into several sections (not shown).
	Casing or Trim: the decorative material (usually wood) that covers from the edge of the window frame to the finished wall (not shown).

Most insulated glass units are double or triple-pane windows that are sealed with an epoxy to create an air gap between each plate of glass. The window frame is perforated on the inside and filled with a desiccant material that absorbs the moisture vapors from between the glass plates. The wider the dry air space, the greater the insulating value of the unit. Manufacturers also use a coating over the glass for greater energy efficiency. The coating is often called low-emission or low E glass. Low E glass reflects radiant heat in the summer and retains interior heat in the winter. Very few manufacturers hermetically seal or create a dry air gap between the panes and then use an air tight seal. Anderson Windows switched from hermetically sealing the window to using the epoxy and desiccant method.

The double-paned window uses 1/8 inch or 3/16 inch glass separated by a 1/2-inch, 3/4-inch or 1-inch air space. A double-paned window is different from an insulated glass unit, because the glass panes are not sealed to create an insulated air space. Consequently, the panes can be replaced without replacing the entire sash.

 

Types of Windows:
 

There are six basic window designs:

Hung Windows:

The double-hung window, which has been used since the 1700s in the United States, consists of a lower and upper sash, each working independently of the other. The sashes move up and down and are often balanced by weights hung on ropes, chains or other balanced devices. The weights counter-balance the weight of the sash and make it possible to set the window open at any position. A modern, double-hung window uses springs on each side of the sash to hold the sash in place. A variation of the double-hung window is a single-hung window, where the top sash is fixed and only the bottom sash is moveable. The double-hung window generally allows a maximum of 50% of the total window area to be used for ventilation. In other words, when the window is open as far as it will go, the two sashes are doubled up and only half of the window space is actually allowing air to pass through the opening.

Casement Windows:

A window that is becoming extremely popular in today’s construction is the casement window. These units are hinged at the sides and swing out and in, like a door. The sashes are opened and closed either by a crank, a push bar mounted on the frame, or a handle fastened to the sash. The benefit of using a casement window is that 100% of the total window area is available for ventilation. If the casement unit pivots outward, the screens are located on the interior portion of the window frame. Casement windows that are 4 to 6 feet or higher tend to have more problems than shorter/smaller windows. The single operator at the bottom may have difficulty opening or closing the window properly at the top if there is a small amount of friction.

Sliding Windows:

Another type of window design is the sliding window unit, in which two or more window panes pass each other on a horizontal track. Sometimes, one of the two sashes is fixed, while the other sash is moveable. Much like the double-hung unit, only 50% of the total window area is available for ventilation. Generally, the sliding windows are of aluminum construction and found in the lower end of the sales or construction market.  A major disadvantage of the aluminum windows is difficulty in obtaining replacement parts, such as rollers or corner retainers.

Awning Windows:

Awning windows contain one or more top-hinged, outward swinging sashes. When open, the sashes extend out at an angle and resemble an awning. There are four variations of awning design: (1) the top-hinge window, similar to an awning window except that it opens inward instead of outward; (2) the utility window, sometimes called a “hopper” window, hinged at the bottom and usually found in basement windows; (3) the jalousie window, which contains a series of horizontal glass panes that open outward; and (4) the transom window, which is sometimes found above interior doors. All of the awning windows provide 100% of the total sash area for ventilation.

Fixed Windows:

Another window design is the fixed window, which consists of a frame and does not contain movable sash components. Examples of fixed windows are: picture windows, decorated bay windows, and the 3/4 round window often found in the gable ends of older houses on either side of the chimney. Fixed windows, as the name implies, provide no ventilation.

Skylights:
The roof window, or skylight, can be fixed with a flat pitch, vaulted, ridge, pyramid or dome design, or a vented window equipped with a manual or power-operated sash. To keep rain out of the building, the vented skylight does not open as wide as the awning windows. Therefore, the effective ventilation area of the vented skylight is considered to be no more than 50% of the total skylight area. And in many cases, it is less than 30%.  Skylights should be installed on curbs with metal step and counter flashing.

 

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