September 26, 2019
The geometry requirements for the installation of ASSY self-tapping screws are dictated by the ICC code-approval in the United States and CCMC code-approval in Canada. The Eurocode 5 distinguishes between pre-drilling holes and not pre-drilling holes to determine accurate geometry requirements. The code approvals in Canada and the USA reflect the geometry requirements set in the Eurocode 5 for self-tapping screws with no pre-drilling as stated in Table 8.2.
The values presented within these approvals also take into account that some wood species such as Douglas Fir are generally more prone to splitting and require higher spacing, end, and edge distance requirements. MTC Solutions’ test data seems to show that these requirements may be conservative, even when considering the splitting risks.
For pre-drilled ASSY self-tapping screws, the geometry requirements are determined according to the relevant wood design codes in each country. The pre-drilling requirements in the Canadian Structural Screw Design guide reflect the values for spacing, end, and edge distances in the CSA-086. The geometry requirements for pre-drilled screws in the USA Structural Screw Design guide reflect the values for spacing, end, and edge distances presented in the NDS 2018.