The primary purpose of windows is to allow the entry of light and air, but they may also be an important part of the architectural design of a building. Windows and their frames are millwork units that are usually fully assembled at the factory, ready for use in buildings. These units often have the sash fitted and weather stripped, frame assembled, and exterior casing in place, Standard combination storms and screens or separate units can also be included. Wood components are treated with a ater-repellent preservative at the factory to provide protection before and after they are placed in the walls.
Insulated glass, used both for stationary and move-able sash, consists of two or more sheets of spaced glass with hermetically sealed edges. It resists heat loss more than a single thickness of glass and is often used without a storm sash.
Window frames and sashes should be made from a clear grade of decay-resistant heartwood stock, or from wood that has been given a preservative treatment. Examples include pine, cedar, cypress, redwood, and spruce.
Frames and sashes are also available in metal. Heat loss through metal frames and sash is much greater than through similar wood units. Glass blocks are sometimes used for admitting light in places where transparency or ventilation is not required.
Windows are available in many types. Each type has its own advantage. The principal types are double-hung, casement, stationary, awning, and horizontal sliding. In this chapter, well cover just the first three.
The double-hung window is perhaps the most familiar type of window. It consists of upper and lower sashes (fig. 4-23 detail) that slide vertically in separate grooves in the side jambs or in full-width metal weather stripping. This type of window provides a maximum face opening for ventilation of one-half the total window area. Each sash is provided with springs, balances, or compression weather stripping to hold it in place in any location. Compression weather stripping, for example, prevents air infiltration, provides tension, and acts as a counterbalance. Several types allow the sash to be removed for easy painting or repair.
Figure 4-23.-Typical double-hung window.
The jambs (sides and top of the frames) are made of nominal 1-inch lumber; the width provides for use with drywall or plastered interior finish. Sills are made from nominal 2-inch lumber and sloped at about 3 inches in 12 inches for good drainage. Wooden sash is normally 1 3/8 inches thick. Figure 4-24 shows an assembled window stool and apron.
Figure 4-24.-Window stool with apron.
Sash may be divided into a number of lights (glass panes or panels) by small wood members called muntins. Some manufacturers provide preassembled dividers, which snap in place over a single light, dividing it into six or eight lights. This simplifies painting and other maintenance.
Assembled frames are placed in the rough opening over strips of building paper put around the perimeter to minimize air infiltration. The frame is plumbed and nailed to side studs and header through the casings or the blind stops at the sides. Where nails are exposed, such as on the casing, use the corrosion-resistant type.
Hardware for double-hung windows includes the sash lifts that are fastened to the bottom rail. These are sometimes eliminated by providing a finger groove in the rail. Other hardware consists of sash lockss or fasteners located at the meeting rail. They lock the window and draw the sash together to provide a wind-tight fit.
Double-hung windows can be arranged in a number of waysas a single unit, doubled (or mullion), or in groups or three or more. One or two double-hung windows on each side of a large stationary insulated window are often used to create a window wall. Such large openings must be framed with headers large enough to carry roof loads.
Casement windows consist of side-hinged sash, usually designed to swing outward (fig. 4-25). This type can be made more weathertight than the in-swinging style. Screens are located inside these out-swinging windows, and winter protection is obtained with a storm sash or by using insulated glass in the sash. One advantage of the casement window over the double-hung type is that the entire window area can be opened for ventilation.
Figure 4-25.-Out-swinging casement sash.
Weather stripping is also provided for this type of window, and units are usually received from the factory entirely assembled with hardware in place. Closing hardware consists of a rotary operator and sash lock. As in the double-hung units, casement sash can be used in a number of waysas a pair or in combinations of two or more pairs. Style variations are achieved by divided lights. Snap-in muntins provide a small, multiple-pane appearance for traditional styling.
Metal sash is sometimes used but, because of low-insulating value, should be installed carefully to prevent condensation and frosting on the interior surfaces during cold weather. A full storm-window unit is sometimes necessary to eliminate this problem in cold climates.
Figure 4-26.-Typical use of stationary window in combination with other types.
Stationary windows, used alone or in combination with double-hung or casement windows (fig. 4-26), usually consist of a wood sash with a large single pane of insulated glass. They are designed to provide light, as well as be attractive, and are fastened permanently into the frame. Because of their size (sometimes 6 to 8 feet wide), stationary windows require a 1 3/4-inch-thick sash to provide strength. This thickness is required because of the thickness of the insulating glass.
Other types of stationary windows may be used without a sash. The glass is set directly into rabbeted frame members and held in place with stops. As with all window-sash units, back puttying and face puttying of the glass (with or without a stop) will assure moisture-resistance windows (fig. 4-27).
Figure 4-27.-Fixed glass in wood stops.