Oriented Strand Board commonly called OSB, is a substitute for plywood used to save the initial cost of installation. Unlike standard plywood, which generally withstands several cycles of wetting and drying, OSB typically starts to deteriorate upon its first exposure to moisture. Upon getting wet, OSB swells up to 20% of its original thickness which results in a loss of strength and density. Unlike standard plywood sheets, OSB does not regain its strength when it drys. When OSB swells, the nails holding it in place may lose their effectiveness resulting in a structure with less of an ability to withstand earthquakes. Due to its characteristics, OSB should be maintained on a strict schedule.