Development of an objective selection method for cedar wooden-shingle boards as roofing material

Cedar wooden-shingle boards, a traditional Japanese roofing material, are handmade by craftsmen using traditional techniques. Product selection is left primarily to the roofers, whose selection criteria are visual and not quantified. In this report, semi-structured interviews were conducted with the roofers in order to clarify the points that the roofers pay attention to when selecting the boards. The comments were analyzed using text mining techniques to classify the view point and evaluation criteria. From all the comments, 622 segments on the basis of meaning unit were extracted for analysis and further aggregated into 18 categories. The results showed that the focus of the roofers was “shape” (77.3 %) and “material color” (22.7 %) of the boards, indicating a relatively high level of attention to the “shape”. In addition, “koguchi” was mentioned relatively more frequently in the part of the boards that surfaces after construction, and this tendency was confirmed across both “shape” and “material color” categories. And as for the width of the cedar wooden-shingle boards, negative evaluations increased when the width exceeded 125 mm. It can be inferred that the roofers suggested the ideal width of the boards considering the characteristics of the cedar tree species. This survey suggests that narrower board widths may be available when the species is limited to cedar. This means that the boards can be produced from cedars of a younger age than the standard theory, which may contribute to the effective use of forest resources and lower prices for the boards.