New Zealand produces grades of dimension lumber by both visual and mechanical grading. A system of in-mill quality verification was set up after concern was raised over the changeable quality of visually graded lumber from fast-grown forests. The same system of quality verification is applied to the lumber regardless of the method of grading - visual, mechanical or a combination of both. Quality records are analysed to show the limitations and effectiveness of the QC system, and of the grading methods.
This article describes the history of timber building in NZ and the development of strength grades. Concern is raised at the need for revision of the grading system in the light of new knowledge.