All parts of a window except the glass itself can be made from a variety of materials. Windows are available made from vinyl, fiberglass, wood compounds, and aluminum. Even with the variety of new materials available, wood windows remain an excellent choice. Sometimes homeowners are confused with all the terminology associated with wood windows.
The jamb is the wooden area that fits between the window and the building. The bottom of the jamb, the part that is parallel to the floor, is the sill. When part of the sill extends into the room, it is properly called the stool, but is usually called the windowsill. The jamb is attached to the building wall. The jamb is seldom replaced.
The sash is the part of wood windows that is actually attached to the glass. If a window is being replaced, both the sash and the glass it contains will be removed. The vertical parts of the sash are the stiles. The horizontal parts of the sash are the rails. Double-hung wood windows have two sashes, and upper and a lower. The upper sash may slide down to open, but more typically the lower sash slides up to open. In double-hung wood windows, the bottom rail of the upper sash and the top rail of the lower sash overlap when the windows are closed. The overlapping rails are called check rails or meeting rails.
The pieces of glass in wood windows are called panes or lights, sometimes spelled lites. In the past, certain combinations of lights were common, such as twelve-over-twelve for the two sashes of double-hung wood windows. Thin strips of wood called muntins hold the panes in place. This arrangement of panes is so attractive that today muntins are sometimes applied decoratively to both surfaces of a large window. These windows are formally called simulated divided lights, or SDL.
Wood windows are an environmentally friendly choice when the wood is sustainably grown and harvested. Properly installed and maintained wood windows do not allow any more heat loss than vinyl or aluminum windows, provided the same quality of glass is used. Wood windows pose no threat to human health, unlike PVC or vinyl, which can emit toxic byproducts.