A design code is a document that sets rules for the material selection, design, manufacture, commissioning, testing and in some cases operation of a structural component or system. They are often a collection of practical operational, theoretical and experimental knowledge and experience.
As such, they are living documents subject to continual review and refinement. They are more regulatory than other forms of guidance commonly used. Factors such as the safety significance of the component, intended function and duty and country of operation influence the design code required to be used in a particular situation.
Changes to design codes can affect both designs for future builds and existing structures. Whilst the regulations may change as a result of recent research in materials, or through new industrial experience, alteration may or may not be required to existing structures that were previously design code compliant.