Fire performance of external wall claddings under a performance-based building code

New Zealand Building Code performance requirements relating to fire performance of external walls are considered and methods of evaluating the potential for vertical fire spread are discussed. Classifying external wall claddings on the basis of performance in the 'combustibility' test has proved overly restrictive where some external cladding materials are concerned. Performance criteria based on heat release or 'degree of combustibility' are proposed and they seem to provide a better classification scheme for external wall cladding materials. Heat release test data for ten different external wall cladding materials are presented.