This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Wherever there is an opening in the wall of a wood building, such as a window or a door, the outside finish, consisting of shingling, clapboarding, or other covering, has to be cut through, and if no special provision were made for the finish around the opening there would be as a result a very ragged appearance. In order to avoid this it is customary to place all around the window opening pieces of finished timber which are known as outside trim, outside architrave, or outside casing. These pieces form a stop for the wall covering.
Fig. 304 shows a window opening in elevation looking from the outside and showing the outside trim. At A is shown the casing around the sides and head of the window and at B is shown the sill. In Fig. 305 is shown a section through the sill at the outside of the wall. Here, A is the sill itself which extends through the wall to the inside and receives the sash as will be explained later; B is the rough framing for the opening and this piece goes between the vertical studding at the sides of the rough opening; C is the outside boarding attached to the studding; D is the wall covering of shingles or clapboards; and E is building paper which must be placed between the outside boarding and the wall covering. It will be noticed that the under side of the sill is ploughed to receive the shingles or clapboards and that it projects out over the wall line a distance of about 1 inch, so as to let rainwater drip to the ground without touching the wall. This figure shows the simplest sort of sill, such as would be used only for very cheap work. In more important work it is customary to add another piece, called an "apron," under the projecting part of the sill, as shown in Fig. 306, where A is the apron, B is the sill, and C is the wall covering. The purpose of the apron A is to cover the joint between the wall covering and the sill and to give it a finished appearance. Fig. 307 shows a section taken through the side or jamb of the window shown in Fig. 304. Here, A is a section through the vertical studding at the sides of the rough opening, B is the outside architrave with the molding C attached to it, F is the outside boarding, G is the building paper, and E is the wall covering of clapboards or shingles.
Fig. 304. Elevation of Window Showing Outside Trim.
Fig. 305. Section through Sill at Outside of wall.
Fig. 306. Sill Details Showing Use of "Apron".
The outside architrave B is nailed at one side directly into the studding, and at the other side it is ploughed so as to join into another piece called the "pulley stile," the purpose of which will be explained later. This pulley stile must be placed at least 2 1/4 inches from the studding A, leaving a space marked H in the figure, which is called the "weight box" or "pocket," in which are placed the weights for operating the window. The arrangement of these weights will be explained in detail later. It will be seen that the width of the outside architrave B is determined by the width of the weight box which it has to cover. It will also be seen that the architrave B projects beyond the pulley stile D by a small amount at the point marked K in the figure. This projection is usually about 1/2 inch and is for the accommodation of the sashes. The purpose of the molding C is to form a projection against which the shingling or the clapboards can be stopped. The building paper G should be carried around as shown and the wall covering placed over it, so as to thoroughly cover the joint between the outside boarding and the molding C. This is to keep the weather from entering the building through this joint. If more room is required in the weight box this may be obtained by setting the outside architrave B outside of the outside boarding, as shown in Fig. 308. The molding C may then be dispensed with if desired, since it is no longer required as a stop for the wall covering, which can stop against the edge of the outside architrave B.
Fig. 307. Section through Window Jamb.
Fig. 303. Another Form of Window Jamb Construction.