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Re: Failure of Connection between Rafter and Ridge Bea

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Many years ago, I looked at a large roof that collapsed under full snow
load. I noticed that the contractor had changed the detail at the ridge.
Instead of cutting the rafters (not I-joists) to bear flat on the ridge
beam (as detailed), he had installed a plate, beveled on two sides,
which the rafters were toe nailed to. There was no tie between the
opposing rafters.

It should be obvious to all of us that a sloped bearing creates  forces
perpendicular and parallel to the bearing surface. This does create a
sliding component that that can actually pull the sloped members off the
bearing, unless there is sufficient tie to prevent this. I would not
count on the diaphragm or friction to prevent this. I would use a tie
strap from rafter to rafter. It is very cheap to do this.

The reason more roofs haven't failed in this manner (in MHO) is most
likely they haven't seen their full design load.

Jim Kestner, P.E.
Green Bay, Wi.