There are two ways of making window and door frames--in three pieces
(two side jambs and one head jamb), or in four pieces (two side jambs,
one head jamb, and a sill piece). When a three-piece frame is used, the
bottom log of the opening is cut or shaped to make the window or doorsill
and the jamb pieces are then fitted to the sill. If the jambs are framed
from pieces of log slabbed on two opposite sides, a presentable frame in
keeping with the log character of the structure is obtained. The window
or door face of the jamb pieces may be rabbeted for the windows and
doors, respectively, or they may have separate wooden pieces, known as
stops, nailed on. The spline on the back of the jamb may be rabbeted out,
or a 2 inch by 2 inch piece of straight-grained wood nailed on. The head
jamb can be framed in the same way; it does not require a spline on the
back. Each side jamb has a dowel framed on each end. The bottom dowel
fits into a mortise in the sill and the top dowel into a similar mortise
in the head jamb.
[Illustration: Figure 15.--Window frames.]
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.
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 2-1/2 to 4 inches
for a door 6 feet 8 inches to 7 feet in height, or 1-1/2 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).
[Illustration: Figure 16.--Log jamb window frame.]
[Illustration: Figure 17.--Typical log-wall section, taken through
window.]
If standard mill work frames are used, false side jambs of sawed
material, usually 2-inch planks, should be fitted in the openings to hold
the logs in place. For a wall made of 10-inch logs, a plank 2 inches by
10 inches should be used for the jambs and the standard frame fitted in
place between them after providing the necessary allowance for the wall
logs to shrink or settle. The head casing ordinarily will cover the space
allowed for shrinkage.
Some kind of insulating material which will take compression, such as
crumpled newspapers, asbestos wool fiber, or rock wool, may be used to
fill the space over the head allowed for settlement. Insulating material
must be installed loosely, so as not to take any weight as the headlog
gradually settles.
[Illustration: Figure 18.--Various ways of framing eaves. Despite the
fact that sawed rafters, as shown above, are often used for convenience
in framing the roof, sawed or milled material is incongruous in
appearance in the exterior of log buildings Hence, pole rafters,
hand-made shakes, and similar hand-riven features are preferred.]
For the log-type frame, copper or galvanized steel flashing should be
fastened to the bottom of the cut in the top log, leaving the lower edge
of the flashing free to slide on the face of the log head jamb. As the
wall settles, the bottom of the flashing can be trimmed off if too much
of the face of the head jamb is covered. This makes a weathertight joint
and protects the insulating material with which the shrinkage space has
been filled. See figure 17, Head section.
[Illustration: Figure 19.--Framing log purlins for shakes.]