These new design and construction methods, however, still have to meet established codes and standards which, if written in a prescriptive way, can be obstructive to the new developments. In the past ten years, there has been a strong move to performance-based standards that emphasise performance rather than conformance to a particular design configuration. These standards allow designs to change radically, provided they still meet the performance objectives set out in the standards. This provides an environment for building materials and systems development that fosters innovation. Appraisals provide both the manufacturer and the user of innovative building products and systems the comprehensive independent assessment they need to demonstrate compliance with either performance or 'deemed to satisfy' requirements.
Appraisals can also be a powerful marketing tool.
Furthermore, it is important to achieve a comprehensive appraisal where there is not only knowledge of the regulations, but also an understanding of how they are interpreted in practice. Here, it is important that there is input from practicing building surveyors in the appraisal process. Another aspect of a complete appraisal is that the product or system must be compatible with components and trades used elsewhere in the building process. Thus, the users of a product or system which has been assessed by this process can be assured that, as far as present knowledge can go the product will meet its intended purpose. Until recently, sarking material consisted of a paper core with various coatings.