This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Fig. 29 shows the plan (a), elevation (b), and section (c) of a French window, together with the general details of its construction. In the plan (a) are seen the double studs b forming the sides of the frame opening, over which the sheathing d is laid on the outside, and the grounds g and lath-and-plaster i on the inside. Extending through the opening, from the sheathing to the grounds, are the jambs a, the joints of which are covered on the outside by the casing, or blind-hanging stile, c, and on the inside by the trim f. Between these jambs, the two sashes are hinged and tongued into the jambs as shown at x, the corners of the stiles, however, being rounded as shown, to permit them to clear the groove in opening. The sashes are hung with small hinges, and the meeting stiles are rabbeted in the same manner as are folding doors, as shown at k n, to enable them to make a tight joint when closed.
In the vertical section (c), taken through the center of one of these sashes, the rough sill of the stud opening is shown at a, while the window sill resting on the veranda floor is shown at c. This sill covers the bottom of the opening from the veranda floor to the inside of the lower sash rail f. This sash rail is grooved on its under side, as shown at e, and the sill is worked with a shoulder, the front of which is also grooved as shown at e' while the top of it is beveled off at the same pitch as the sill. The groove in the front of the shoulder e' tends to prevent water from being blown into the crack during a rain storm, and the slanting sill and grooved lower rail permit the moisture to drip off the latter, and run to the outside of the opening.
At g is shown the section of the middle bar of the window, which is seen in the elevation at g', and at h is shown the top rail of the hinged sash and lower rail of the fixed transom sash k' over it. The hinged sash is but 5 feet 6 inches in height, as this is sufficient to permit the window to be used as a means of ingress and egress, while the full opening is 7 feet high.
In the construction of the window head, the framing is precisely the same as at the sides, shown in the plan (a), except that the jamb j in the top of the window is not tongued as at x in the plan (a).