Prescriptive Vs. Performance: These requirements are usually a combination of prescriptive requirements that spell out exactly how something is to be done, and performance requirements which just outline what the required level of performance is and leave it up to the designer how this is achieved. Historically they are very reactive in that when a problem occurs the building codes change to ensure that the problem never happens again. In recent years there has been a move amongst many building codes to move to more performance requirements and less prescriptive requirements. Traditionally building codes were generally short non complex interrelated sets of rules. They generally included reference to hundreds of other codes, standards and guidelines that specify the details of the component or system design, specify testing requirements for components, or outline good engineering practice. These detailed codes required a great deal of specialization to interpret, and also greatly constrained change and innovation in building design. In recent years several countries, beginning with Australia, have moved to much shorter objective based buildings codes. Rather than prescribing specific details, objective codes lists a series of objectives all buildings must meet while leaving open how these objectives will be met. When applying for a building permit the designers must demonstrate how they meet each objective