In wood framed construction, it is important to transfer lateral forces from the roof framing to the shear walls below. This can easily be accomplished in a number of ways, but it is often overlooked at the job site. In addition, this connection can be hard to observe once exterior sheathing or house-wrap is in place. Lateral design is an important part of construction and building departments are starting to require lateral design calculations and are looking more carefully for hold-downs and other lateral connections at the site. The purpose of this post is to show several options for how to connect the roof framing to the shear walls below and explain which methods are easier to identify in the field.
At bearing walls, where rafters and trusses bear on exterior or interior shear walls, blocking is the most effective way of transferring lateral forces from the roof to the top plates. We typically see one of three connections: 1. Extend the wall sheathing up past the top plates and fasten it to both the blocking and top plates with edge nailing, 2. Toe-nail the blocking to the top plates per the IRC code or engineers specifications, 3. Fasten the blocking to the top plates with angles, such as Simpson A35 ties. We find that toe-nails and angles can easily be installed both during framing and after the house has been sheathed and wrapped. Extending the exterior sheathing is a good option, but must be pre-planned and can not be inspected once house wrap has been installed.
At gable end walls, the gable end truss must be fastened to the top plates below, to transfer the lateral forces. Again, there are several ways to accomplish this: 1. Extend the sheathing from the gable end truss down to the top plates and fasten it with edge nailing, 2. Toe-nail the bottom chord of the gable end truss to the top plates per the IRC code or engineers specifications, 3. Fasten the bottom chord to the top plates with angles. We typically specify angles between the bottom chord of truss and the top plates because they provide good lateral transfer and can be easily observed at the job site. Extending sheathing and toe-nails can not be observed once the house wrap is installed. Framers typically fasten the sheathing to the gable end truss on the ground, before lifting it into place, and it is hard to leave an extension at the bottom.
Most engineers will include typical details or sections illustrating how to transfer lateral forces from the roof framing to the shear walls below. Discussing this connection with your engineer will help to reduce framing revisions. Angles can usually be installed if sheathing extensions or toe-nails are not installed correctly. This can be expensive, but may be more cost-effective than removing house wrap and siding.
Contact us with you have any further questions about shear transfer and visit the wood framed construction category of our blog for more about residential construction and lateral design.