Including diaphragm action in sizing building posts (columns) and postembedment depths (foundation) is more consistent with the actual building performance. A large portion of in-plane loading, such as wind, is transferred to the end walls through in-plane shear via metal roofing-a phenomenon called "diaphragm action." Because of load sharing and redundancies that are not accounted for, postframe buildings are stronger and stiffer than what is normally assumed. Various construction and design practices that increase diaphragm strength and stiffness of postframe buildings are discussed. The objective of this paper is to discuss design and construction practices that contribute to the diaphragm strength and stiffness of metal-clad postframe rectangular buildings. The paper is based on data and information obtained from the full-scale metal-clad timber-framed postframe building tested over a period of 9 years, and the literature. Understanding the functions, contributions, interactions, and load sharing characteristics of the different framing, cladding, and redundant elements is critical in understanding the diaphragm action and optimizing designs of postframe buildings. The study benefits the engineers, architects, builders, and code officials of postframe buildings.