The most usual style of window in this country is the "double hung" window, which has two sash, each one-half the height of the window and each hung with cords and weights, to slide up and down. The essential features of this window are the same in both frame and brick buildings, although the difference in the character of the walls necessitates some difference in the construction of the frames.
There are also several variations of this type of window, a very common one in brick buildings being that shown at G. Where the window has a circular head there are two methods of constructing the upper part of the frame and sash. One is to make all but the outside portion of the frame square, with square solid corners to the upper sash, so that it will slide up and down, and be finished on the inside the same as if the window had a square head. The other method is to make a solid circular head to the frame, so that it will finish circular on the inside. The latter method generally gives the better appearance on the inside, especially where there are no curtains or draperies to the window, but it has a serious objection in that the lower sash can only slide to the springing of the circle, and the upper sash, having but a small portion of its sides straight, does not usually work well. For these reasons it is generally better to adopt the former method of construction for circular head windows in residences, hotels, club buildings, etc.
Frequently in brick buildings the top of the upper light of glass, and also the outside of the frame, is cut to a segment of a circle, in which case it is called a "segment head" window. Segment head windows are usually finished square on the inside.
Double hung windows are also often made with the division between the sashes at some point above the middle, so as to bring the meeting rail above the height of the eye when looking from the inside ; when this is done it is necessary to make a pocket above the head of the frame for the lower sash to slide into, if it is to slide its full height.
Double hung windows are also frequently used in pairs, as shown at C, and sometimes three or four windows are included in the same frame. A window such as is shown at C is called a "mullion" window or a double window, the vertical division between the windows being called a "mullion." This window also has a "transom," which is the horizontaldivision between the double hung sash and the small sash, or "transom lights," above. Transoms are frequently used where there are no mullions, and vice versa.
Stone mullions and transoms are also frequently used to divide windows, as shown in drawing E, which also represents a special type of the double hung window.
Next to the double hung window, in regard to general use, comes the casement or "French" window shown at D. This window has the sashes divided vertically, each being hinged at the sides like a pair of doors. Transoms are frequently, although not necessarily, used with this style of window. The casement window is the common type of window in Europe, but it has serious objections which make it undesirable for general use. The most important of these objections are that if the sash swings in, it is difficult to make them storm proof, and they also interfere with the shades and draperies, and if they swing out, fly screens cannot be used on the windows.
Besides these two types of windows there are also several varieties of windows in which the sash are pivoted, either at the centre of the sides or at the top and bottom. Windows of the shape shown at / are frequently seen in large buildings. The sash in these windows, if they open at all, are usually pivoted top and bottom.
Then, there are the tracery windows used in churches, which may be of a great variety of shapes and proportions.