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Re: Solid blocking between 2x outlookers

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Jim Wilson wrote:

Does anyone have a clarification on this?

WFCM Table 2.2C has a detail of framing requirements
for gable endwall outlookers.  One note points to the
solid blocking and refers to it as "Required
blocking."  It does not seem clear if it is saying
that blocking IS required, or that blocking is to be
provided as required, as if when designed by an
engineer.

And is blocking always just equal in proportion to the
member it is bracing?  i.e. 2x10 blocking for 2x10
framing, or can smaller pieces be used?

Thanks,
Jim Wilson, PE
Stroudsburg, PA

Jim,
Here is my take on this. If the outlookers are built into a gable truss, the top chord of the truss is notched and the outlookers are installed flat. The diaphragm is continuously connected to the top chord of the gable truss and as long as the diaphragm is boundary nailed, everything is fine.

If, on the other hand, the gable is a pony wall or balloon frame wall where the rafters frame above the plate line. In this case the outlookers will probably be cut into the roof joists (laid flat) and extended over the double top plate of the pony wall that forms the gable end. In this case, you need to add 2x flat blocking between the outlookers to maintain a continuous diaphragm connection to the gable in order to transfer shear.

Next, assuming that the outlookers are not laid in flat but that the pony wall is built to the bottom of the 2x outlookers, then you would install full depth blocking on the edge to complete the shear path from the diaphragm down.

It is more common to lay in outlookers flat and either cut them into a gable truss (designed for the drag load at the end of the home) or on top of a double plate pony wall where the outlookers are cut into the top side (tension) of the joists for at least two joist bays. A continuous blocking is require.

FWIW, this type of construction is used primarily for inexpensive starter homes. The longevity of the outlookers at the gable end does not hold up well over time unless adequately finished to prevent moisture from seeping in. Here in the desert the flat outlookers are exposed, but I'll admit that I've only designed one as I don't really care for this type of roof.

Dennis

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