The main function of a building is to protect the occupants and contents from the weather, principally rain, wind and extremes of temperature. It is most important to provide a simple intact envelope which will achieve all of these functions; features such as windows, flues, damp-proof courses and thermal insulation are only additional sophistications. Obviously a building must be structurally sound in order to survive, and intermediate suspended floors must be capable of resisting any normal imposed loads.