Abstract Wood-based boards were exposed to an outdoor environment at angles of 90° and 45° to the ground surface in order to investigate the effect of exposure angle on board properties. In a study on 5-year outdoor exposure, the effects of the exposure angle varied depending on the type of board. Particleboard (PB) and oriented strand board (OSB) deteriorated faster when exposed at 45° compared with 90°, and the difference was more apparent with longer exposure. Five years of exposure at 45° lowered the retention of the modulus of rupture and internal bond of phenolic resin–bonded PB to 15 and 4 percent, respectively. In contrast, medium-density fiberboard (MDF) showed no difference in deterioration between both exposure angles. After 5 years of exposure, the retention of the modulus of rupture was 70 to 80 percent in MDF, while that of internal bond was 81 to 97 percent, thereby showing that the internal bond was better retained than the modulus of rupture. The high durability of MDF was attributable pa...