Preface This is the fifth edition of CSA O151, Canadian softwood plywood. It supersedes the previous editions published in 2009, 2004, 1978, and 1974. This Standard specifies an in-plant production and quality control system that includes auditing and control by a recognized certification body if applicable. It also provides a mechanism for the specification, quality control, and certification of custom grades and allows the use of alternative overlay systems. Changes to this edition include the following: a) updated some publication references; and b) clarified the basis for ply thicknesses specified in Table 2. Scope 1.1 This Standard applies to exterior bond, all-veneer plywood that has a minimum of three plies and whose outermost plies have parallel grain direction. 1.2 This Standard specifies requirements for a) a quality system; b) ply species; c) materials; d) panel construction; e) bonding; f) veneer and panel grades; g) dimensions and tolerances; h) marking; and i) testing. 1.3 In this Standard, \"shall\" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the Standard; \"should\" is used to express a recommendation or that which is advised but not required; and \"may\" is used to express an option or that which is permissible within the limits of the Standard. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.