In order to assess the mechanical durability of wood-based panels, roof sheathing panels that had been used in a model house for nine and a half years were collected and investigated for deterioration of lateral nail resistance (LNR), nail head pull-through resistance (NHPT), internal bond strength (IB), bending strength (MOR), and bending stiffness (MOE). The roof sheathing panels used are an aspen oriented strand board (OSB(A)), a Scots pine orieted strand board (OSB(P)), a phenol-formaldehyde resin bonded particleboard (PB(PF)), a methylene diphenyl diisocyanate resin bonded particleboard (PB(MDI)), a melamine-urea-formaldehyde resin bonded medium density fiberboard, and a structural plywood. The panel moisture content through the year ranged from around 6 to 11%, which was estimated based on the equilibrium moisture contents of each panel and the attic temperature and humidity. Due to such arid conditions, there was no significant deterioration of MOR or MOE in any of the panels. There was some deterioration in IB, however, except in OSB(P) and PB(PF) which showed the largest IB reduction of 21 to 25%. In connection with this decrease in IB, the LNR of PB(PF) exhibited a statistically significant reduction of 24%, while other panels showed no significantly reduced by 6 to 26% according to the panel type. The factors that affect NHPT were investigated by conducting some additional tests in terms of panel upper surface demage caused by nail-head pressing, panel lower surface damage caused by nailing, repeated heating of nails caused by high temperatures in excess of 80℃ on the roof surface especially in summer, and so on. From the test results it was found that part of the reduction in NHPT was explicable by the damage to the upper panel surface below the nail head, and the rest could be potentially explained by dew condensation on the nail shanks, which affects bond strength between panel elements surrounding nail shanks.
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