Figure 2-19. Typical rafter truss for a TO type building.
(1) Rafters. The rafters or upper
system. You can see that they are attached to the
chords are the same as the rafters in the end panel.
rafter, to the lower chord, and to the stud in the
Their primary function is to carry the roof load to the
studs. NOTE: rafters in end panels are an integral
c. Advantages. The principal advantages
part of the panel and are not considered as rafter
of a trussed rafter system over a plain rafter system
are that smaller size lumber can be used and that the
(2) Lower chord. The lower chord or
truss can be fabricated as a unit for later erection.
ceiling joist is a 1 x 6 member spanning from the
This results in economy of labor and material, and
lower ends of the two rafters in the truss. When a
saves time except on very small projects.
ceiling is used, these members are increased to 2 x 6's
d. Templates or jigs
. Rafter framing
and the ceiling is attached to them.
constructed without the use of ridgeboards may be
(3) Hanger. The hanger is the 1 x 6
rapidly completed by use of a truss assembly jig or
vertical member in the center of the truss that ties in
template. The template is laid out (1, fig. 2-20) to
the peak of the rafters to the center of the lower
form a pattern conforming to the exact exterior
dimensions of the truss. Templates or jigs must be
constructed accurately to assure proper dimensions of
(4) Web members. The web members
the rafter truss. Lay out a jig in the following manner
are the diagonal braces which tie in the center of the
(2, fig 2-20):
lower chord with the centers of the rafters. They are
cut from 2 x 4's.
(1) Measure and mark a straight line on
a selected surface, the exact length of the joists which
(5) Rafter tie. The rafter tie, normally
will form the chord of the truss. This is the base line
a piece of 1 x 8, connects the two rafters at the peak
of the truss as in the end panel.
(2) From the center of the base line and
(6) Knee braces. Knee braces are the
at right angles to it, lay out a line the length required
members which tie in the roof system with the wall
to form the leg of a right