The seismic in-plane response of cold-formed steel (CFS) framed diaphragm structures has not been the subject of extensive study. The information available specific to diaphragm design in the North American CFS design standard is based on limited experimental work and the extrapolation of design methods developed for the wood industry. Nonetheless, buildings having floor and roof diaphragms framed with thin steel joist members and wood sheathing panels are being constructed in North America. To address these shortcomings a test-based research project was carried out at McGill University. The objective was to provide characterization of typical CFS framed / wood-sheathed diaphragm response to in-plane lateral loading, in order to better understand the structural performance, and to provide full force vs. deformation hysteretic parameters for use in subsequent design method development and nonlinear response history analyses of CFS framed structures. This research was a complementary study to the CFS – NEES a project, which involved the dynamic testing of a full-scale two storey CFS framed building. The work detailed herein includes diaphragm test specimens that were based on the floor and roof configurations used in the CFS - NEES Building. The objective was to obtain information regarding the response to loading of the isolated diaphragm systems. The specimens were comprised of oriented strand board (OSB) sheathing screwed to CFS C-Channel joists. Eight 3.66 x 6.1m diaphragm configurations were tested under monotonic and reversed cyclic loading. Design predictions for the shear strength and stiffness of the diaphragm configurations are also included following the provisions of the AISI S213 & AISI S400 Standards.