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Tall Heel Truss

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    Harry Whitver

    The Forces

    In a wind or seismic event, there are typically two forces involved. Lateral load is the sideways force, also called “shear”, that causes trusses or rafters to want to slide on the top plate. The second force is uplift that causes the roof to lift vertically from the wall. Proper design connects each truss or rafter to the wall strongly enough so that these forces are transmitted positively.
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    Harry Whitver

    Tall Block

    In this method, a tall block of LSL, LVL, or 2x is placed between each truss. The roof diaphragm is edge nailed to the block, and the truss bottom chord is connected to the shear wall with a hurricane clip. Vent holes may be notched or drilled into the block as necessary.
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    Harry Whitver

    Sheathing—No Splice

    In this case, the connection is made by the wall sheathing itself. If the sheathing is continuous over the truss/top plate intersection, as shown, a hurricane clip is not needed. This method requires a block large enough to be edge nailed to both the roof sheathing and the wall sheathing.
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    Harry Whitver

    Sheathing—Spliced

    This method is similar to the previous one except that the wall sheathing stops at the truss/top plate intersection. Separate sheathing is added between each truss, and edge nailed to blocking. Note that this blocking could be simple 2x blocks, a pre-fabricated wall section, or truss piece. A hurricane clip is required.

The truss to shear wall connection is one of the most important links in the lateral force load path, but that extra heel height makes the connection a challenge.

When the wind howls or the earth shakes, roofs and walls must work together or the entire building can fold like a paperback novel. That’s because roofs are horizontal diaphragms that distribute lateral (wind and seismic) loads to walls, which, in turn, transfer them to the foundation.

When a structural failure occurs it’s usually a connection coming apart rather than the rupture of a beam, column, or other structural element. With stick-framed construction, the two most notorious connection failures are the roof to wall, and the floor to foundation.

Building codes are thorough at describing the forces involved but sketchy at best when it comes to detailing it all out. Here are three methods to ensure positive load transfer at a tall heel truss.

Tim Garrison, P.E., The Builder's Engineer