The New Zealand Building Code (NZBC) is performance based. From a durability perspective, compliance requires a practitioner to demonstrate that materials will remain functional for the minimum periods specified. The NZBC also states that buildings must be constructed to avoid the likelihood of fungal growth or the accumulation of contaminants on linings and other building elements. Currently, there is no recognised method for practitioners to use to demonstrate that a wall system can meet this requirement for the required design life. In this paper, we consider how hygrothermal modelling, in conjunction with the VTT mould index, may be used to form the basis of such a method. In the past, there has been a discrepancy between predicted failures and field evidence, but the VTT mould index appears to correlate much better with the successful in-service history of typical New Zealand construction.
Hygrothermal performance of New Zealand wall constructions — meeting the durability requirements of the New Zealand Building Code