Strand plies are positioned as alternating layers that run perpendicular to each other. This structure mimics plywood. Waferboard, a weaker and less-stiff cousin of osb, is a homogeneous, random composition. Osb is engineered to have strength and stiffness equivalent to plywood. Performance is similar in many ways, but there are differences in the service provided by osb and plywood.
All wood products expand when they get wet.
When osb is exposed to wet conditions, it expands faster around the perimeter of the panel than it does in the middle. Swollen edges of osb panels can telegraph through thin coverings like asphalt roof shingles. The term ghost lines or roof ridging was coined to describe the effect of osb edge swelling under thin roof shingles. SBA correctly indicates that dry storage, proper installation, adequate roof ventilation and application of a warm-side vapor barrier will help prevent roof ridging. Irreversible edge swelling has been the biggest knock on osb.