Scheffer index as preferred method to define decay risk zones for above ground wood in building codes

Building codes and wood preservation standards are gradually taking more account of variations in climate within and across national boundaries. In Canada, the NRC-IRC Moisture Index (MI) has been used to delineate the boundary of zones where above ground wood exposed to precipitation or conducive to moisture accumulation needs to be preservative treated to Canadian Standards Association wood preservation standards. However, the older Scheffer Index is more widely recognised in wood science circles. Above ground field test data were reviewed for experiments where matched material had been exposed at more than one test site for a sufficient period for decay to occur. The relative condition of this material at two sites was compared to the Scheffer Index values for the sites and whether the MI values were below or above 1·0. The Scheffer Index was found to be a more reliable predictor of decay condition for above ground outdoor wood applications.