In a four-piece frame, the sill log is cut with a slope, in the customary way, and the jambs are fitted as for a three-piece frame. [Figure 15] illustrates the installation of three- and four-piece window frames.
Figure 16.—Log jamb window frame.
When the head jamb or top log over the opening is reached, the frames are ready for installation. The opening is now cut out, the sill fashioned, the vertical spline slot framed, and the head jamb log cut out to fit over the opening. At this point, the amount of settlement resulting from the shrinkage of the wall logs, as they dry out, must be determined and a corresponding allowance provided in the opening. This allowance is made between the upper side of the headpiece of the frame and the bottom of the log directly over the opening, and should be from 2½ to 4 inches for a door 6 feet 8 inches to 7 feet in height, or 1½ to 3 inches for an ordinary double hung window. The log over the opening should be notched out on the under side so that it can be dropped in place after the frame has been set in position.
When the type of window or door frame here described is used, neither outside nor inside casings, sometimes called wood trim, are required. The logs selected for the jamb material should be from 2 to 3 inches larger in diameter than the wall logs, in order to fit properly. Also, they will be much easier to work if well-seasoned ([fig. 16]).
