A testing program related to the evaluation of the mechanical properties of CLT diaphragms used in construction was carried out by the Advanced Building Systems (ABS) Department of FPInnovations in response to a request made by the Client, Nordic Engineered Wood Products. The main objective of this study was to determine the in-plane stiffness and potentially strength properties of CLT panels used in diaphragm applications. The test matrix consisted of three (3) series of two (2) specimens each. The CLT specimens were tested under third-point loading during the program. All specimens were manufactured by Nordic Engineered Wood Products and delivered to FPInnovations’ testing facilities in Québec City. The CLT panels were made of nominal 2×4 Black Spruce lumber (CLT Grade E1 – ANSI PRG 320).