In many places where windows with a single sash are used, it will be found better and more economical to pivot them at the centre of the sides than to hang them on hinges. In audience rooms, especially, this is a very good arrangement for small windows, and even sash 8 and 10 feet high are often pivoted in this way. By swinging the sash out at the bottom, and in at the top, the danger from leakage is not much greater than in a double-hung window. The frames for such windows should always be made of plank ; they should not be rebated, but made as shown in Fig. 112, with stops, S S, nailed partly to the frame and partly to the sash, as shown. Both stops are cut on a bevel near the centre of the window, the upper part of the outside stops being nailed to the frame and the lower part to the sash, while the reverse is the case with the inner stop. The sill joint should be as shown in Fig. 108.
B. Windows Pivoted Top and Bottom. - Large plate glass windows, when of a single light, are generally pivoted at the top and bottom, and when the sash is of an unsymmetrical shape, as in the case of the outer sash in the window shown at 1, Fig. 93, this is about the only practical way of opening the window.
The frames of such windows should be made of plank, and the joint between the bottom rail of the sash and the wood sill should be arranged in a similar manner to that shown for casement sash which open inward.
Fig. 113 shows the detail of the large single light windows in the Odd Fellows' Temple, Philadelphia, and the manner of stopping the sash at the sides appears to the author to be about as good as can be devised. The stop, S, is placed flush with the outside of the sash at one side of the window, and flush with the inside of the sash at the other side, as shown in the plan. Such windows are also constructed in a manner similar to that shown in Fig. 112, with one stop nailed to the inside of the sash and the other to the outside, and the upper stops cut at the centre. Windows up to 5 or 6 feet wide may be pivoted in this way, but the sash should be made quite heavy, and never less than 2 ¼ inches thick.