MiTek engineers frequently receive questions on why the note “Solid blocking is required on both sides of the truss at joints…” appears on an engineering drawing and how to address it. This often arises at the high heel joints. [For all images, See PDF or View in Full Issue.]
According to ANSI/TPI 1-2014 (section 7.3.8.1) and ANSI/TPI 1-2022 (section 7.3.9.1) (National Design Standard for Metal Plate Connected Wood Truss Construction), solid blocking is typically required when a truss member at a bearing location is loaded in compression perpendicular to grain, that member is not laterally restrained and is subject to out-of-plane buckling, and the compression force exceeds the allowable bearing stress or the member fails the buckling check. All these factors are automatically checked by the software.
The software automatically checks the compression perpendicular to grain, and the buckling potential using member depth, width, and modulus of elasticity (E). If buckling is possible, “Solid blocking is required on both sides of the truss at joints…” appears.
The Building Designer is responsible for designing the solid blocking when it is required. It should be placed on both sides of the truss at the joint in question. The blocking must be made of stress-graded 2x lumber (e.g., 2x6 or 2x8), or engineered wood panels (for heels over 15-1/4”), installed tight between the trusses and properly nailed or fastened to trusses, sheathing, and wall framing to resist lateral movement per the Engineer of Record or Building Designer specifications. Solid blocking in truss design plays a crucial role in ensuring structural integrity, load transfer, and compliance with building codes. For multi-ply trusses, ply-to-ply nailing may increase the effective width and reduce buckling risk.
When dealing with trusses with high heels—typically anything over 15-1/4”—solid blocking becomes more than just a framing detail. It is a structural necessity to ensure the integrity of the truss system. It is crucial that the loads are effectively transferred from the truss members to the supporting structure while maintaining balanced stiffness (preventing buckling) throughout the truss system.
For additional information, or if you have questions, please contact the MiTek Engineering department.