Full-scale fire performance evaluation of actual-sized flame-retardant-treated Japanese cedar (Cryptomeria japonica) timber claddings

The objective of this study was to investigate the full-scale fire performance of Japanese cedar (Cryptomeria japonica D. Don.) timber claddings in accordance with the KS F 8414 standard. Visual inspections revealed that the lower sections of the specimens were carbonized, whereas the upper sections, beyond 2000 mm from the fire source, remained unaffected. Temperature measurements indicated that the highest temperature at the exterior of Level 1 (2500 mm from the upper end of the opening) reached 868.8 °C, while the maximum temperatures at the exterior and interior walls of Level 2 (5000 mm from the upper end of the opening) were 557.8 °C and 249.6 °C, respectively. The highest temperature within the cavity layer of Level 2 was 122.2 °C, complying with safety standards that require temperatures at Level 2 to not exceed 600 °C for more than 30 s over a 15-min period. Additionally, the fire performance of flame-retardant treated cedar was compared with that of flame-retardant-treated commercial phenolic foam. Although both materials passed the fire safety evaluation, the cedar timber claddings exhibited stronger heat-transfer-blocking effects, particularly in the cavity layer of Level 2, where the temperature was significantly lower than that for the phenolic foam. These results underscore the potential of flame-retardant-treated cedar timber claddings as a safe and sustainable building material, providing valuable insights into enhancing fire safety in timber constructions.