(2) Collar Beam. A tie or collar beam is a piece of stock (usually 1 by 4, 1 by 6, 1 by 8, or 2
by 4) fastened in a horizontal position to a pair of rafters between the plate and the ridge of the roof
This type of beam tends to keep the building from spreading. Most codes and specifications require
them to be 5 feet apart or every third rafter, which ever is less. Collar ties are nailed to common rafters
with four 8d nails to each end of a 1-inch tie. If 2-inch material is used for the tie, they are nailed with
three 16d nails at each end. This type of bracing is used on small roofs where no ceiling joists are used
and the building is not wide enough to require a truss. The lower the collar beam or chord, the better it
works.
(3) Support. In small roofs that cover only narrow buildings and in which the rafters are
short, there is no need for interior support or bracing. In long spans, the roof would sag in the middle if
it were not strengthened in some way. To support long rafters, braces or other types of supports must
be installed.
(4) Rafter Support. In wide buildings, where the joists or chords must be spliced and there is
no support underneath, the rafter and joists support one another (see Figure 3-16).
d. Knee Brace. If no additional bracing is needed, the truss is set in place on the plates. If
additional bracing is needed, a knee brace is nailed to the chord. The knee brace forms a 45 angle with
the wall stud. For easier erection, the knee brace may be omitted until the rater truss is set in place (see
Figure 3-16).
Figure 3-16. Rafter support detail
3-7. Trusses. A truss is a framed or jointed structure composed of straight
members connected only at their intersections in such a way that if loads are
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EN 5156
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