end of a roof rafter. This location on the
rafter is not subjected to as much bearing stress as the middle of the rafter, but
could still result in a failure from compression stresses.
In Figure 4, checks have developed into
larger cracks that are following the grain.
Unfortunately, the grain is not parallel to
the long axis of the board and angles inward toward the neutral axis of the joist.
The bending stress at the lower part of
the joist will eventually drive the crack
through the board, causing failure.
Failures of framed roofing systems
occur from a variety of causes including
the existence of defects in wood. Many
roof framing failures have occurred under normal loading because of the reduced strength in wood framing from
the defects mentioned above. Inspection of the failed framing will help determine the role of defects in the cause
of the loss.
Figure 1 Figure 2
FAILURE WAS AN OPTION
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Figure 4 Figure 3