When to use this Guide
- Use this Design Guide if:
- The roof is a Blocked Diaphragm, and
- The building was designed per the requirements of the International Building Code® (IBC®)
- If the roof is a Blocked Diaphragm but the building is a single-family, two family or townhouse, refer to Roof Ridge Design Guide for Blocked Roof Diaphragms meeting the requirements of the International Residential Code® (IRC®).
- If the roof is an Unblocked Diaphragm, refer to Roof Ridge Design Guide for Unblocked Roof Diaphragms
- If in doubt, check with the local building code official or a registered design professional to verify the type of roof diaphragm and building for your specific project
What is a Blocked Diaphragm?
- A Blocked Diaphragm is one in which blocking (e.g., 2x_ lumber) is require between the framing members (i.e., rafters or trusses) and all edges of the wood structural panels (i.e., plywood or Oriented Strand Board OSB) must be supported by and attached to the framing members and blocking
- Blocked Diaphragms are typically required in high wind or seismic zones
- If in doubt, check with the local building code official or a registered design professional to verify the type of roof diaphragm used for your specific project
Why use Shear-X?
- Shear-X brackets are designed to transfer in-plane shear forces at the ridge line of roof diaphragms
Why use Shear-X?
- The brackets allow the use of continuous ridge venting in blocked diaphragms by replacing the boundary nailing between the roof sheathing and the ridge board/ridge beam that is lost due to the gap required for venting
Roof Ridge Installation
- The brackets can be bent to accommodate any roof pitch from flat to 12:12
- The design values for the Shear-X brackets have been developed by an ISO/IEC 17065 Accredited Product Certification Body based on testing by an ISO/IEC 17025 Approved Agency
- The roof diaphragm must be sheathed with plywood or OSB wood structural panels installed per the requirements of the building code and the construction documents for the project
- Framing members (i.e., rafters and trusses) must be minimum 2x4 SPF No. 2
- Shear-X brackets installed in blocked diaphragms require a continuous ridge board/ridge beam/riser of minimum 2x6 SPF No. 2 for rafter construction and 2x4 SPF No. 2 for truss construction
- Attach the rafters/trusses to the ridge beam/ridge board/blocking with a minimum of (3) 12d (0.131”x3-1/4”) smooth shank nails (toenailed)
How to use the table
- Use the following table to determine the required on-center spacing of the Shear-X brackets along the ridge line when continuous ridge venting is used with a blocked roof diaphragm designed per the requirements of the International Building Code (IBC)
- Note - The table was developed using the lowest allowable shear values for the Shear-X brackets, which vary by bracket size and roof pitch.
- For a more exact analysis, refer to DrJ Technical Evaluation Report (TER) No. 1509-03 and use the allowable shear load that most closely applies to the specific conditions
- The following 11 steps provide a tutorial on how to use the table to determine the required spacing of the Shear-X brackets when continuous ridge venting is used with a blocked roof diaphragm
- The information required to use this table is typically provided by the building designer in the construction documents for the building
- Select the controlling lateral load condition (i.e., Seismic or Wind)
- For example: Seismic
- Select the “Case” to be used for the wood structural panel diaphragm pattern (i.e., 1, 2, 3, 4, 5 or 6)
- For example Cases 1 & 3
- Select the “Boundary” and “Other-Panel-Edge” nailing pattern to be used based on the diaphragm Cases and nailing pattern specified by the building designer
- For example – Cases 1 & 3 with Boundary nailing at 6” oc and Other-Panel-Edge nailing at 6” oc
- Select 16” or 24” Shear-X bracket based on the on-center spacing of the roof framing members (i.e., rafters or trusses)
- For example, roof is framed with trusses at 24” oc
- Find the Panel Sheathing Grade used
- For example – The building designer has specified the roof sheathing to be 15/32” 32/16 span rated OSB. This type of panel is classified in the IBC and IRC as Sheathing Grade
- Find the Nail Size used to attach the sheathing to the trusses and blocking
- For example – The building designer has specified 8d (0.131”x2-1/2”) common wire nails.
- Verify the Minimum Fastener Penetration into the trusses and blocking based on the Nominal Panel Thickness specified
- For example – The roof sheathing will be 15/32” OSB attached to the trusses and blocking with 8d (0.131”x2-1/2”) common wire nails.
- Therefore the penetration of these nails into the framing and blocking will be 2-1/2”-15/32” = 2-1/32” >1-3/8”.
- Verify the Nominal Width of framing and blocking to be used
- For example – The building designer has specified that the roof trusses and diaphragm blocking must be nominal 2x_ material oriented vertically.
- Determine the maximum on-center spacing of the Shear-X brackets to be installed along the ridge line
- Lay out brackets along roof ridges at spacing indicated in the table
- Each roof segment needs a minimum of two brackets, one at each end.
- Attach brackets as described in Shear-X™ Roof Ridge Installation Guide for Blocked Roof Diaphragms