When to use this Guide
- Use this Design Guide if:
- The roof is a Blocked Diaphragm, and
- The building is a single-family, two-family or townhouse meeting the requirements of the International Residential Code® (IRC®)
- If the roof is a Blocked Diaphragm but the building does not meet the requirements of the IRC, refer to Roof Ridge Design Guide for Blocked Roof Diaphragms designed per the requirements of the International Building Code® (IBC®).
- 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
- The brackets allow the use of continuous ridge venting in blocked diaphragms by replacing the boundary nailing between the roof sheathing and the ridge beam/ridge board 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 beam/ridge board of minimum 2x6 SPF No. 2 for rafter construction and 2x4 SPF No. 2 blocking 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 in single-family, two-family and townhouses meeting the requirements of the International Residential Code (IRC)
- For a more exact analysis and bracket spacing, refer to Shear-X bracket spacing table developed for blocked diaphragms designed per the International Building Code (IBC) or DrJ Technical Evaluation Report (TER) No. 1509-03.
- The following four 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 in single-family, two-family and townhouses meeting the requirements of the IRC.
- Determine the nominal thickness of the roof sheathing (i.e., plywood or OSB) currently installed (or to be installed)
- For example – the sheathing is 15/32” 32/16 span rated OSB as determined from the grade stamp located on the attic side of the panels
- 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 spaced at 24” oc. Therefore, use Shear-X 24” brackets with maximum spacing of 6’-0” oc.
- 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.