Comparison of Certain Structural Properties Among 3-Ply, 4-Ply and 5-Ply, 1/2-Inch Southern Pine Plywood Sheathing
Abstract
An evaluation of three constructions 3-ply, 4-ply and 5-ply, 1/2-inch-thick southern yellow pine plywood sheathing as subfloor and roof was made. The evaluation considered only flexural properties, panel shear properties and dimensional stability in relation to panel cost, though other properties are recognized as being important too.
Among the three constructions considered, the 3-ply can support higher flexural loads and deflect less as subflooring than can the 4-ply and 5-ply constructions when panels used with face grain orientation parallel to span (perpendicular to the direction of joists). Specifically, at 16-inch spans, flexural strength and stiffness of 3-ply panels are approximately 8% higher than those of 4-ply panels while the manufacturing cost of 3-ply plywood is approximately 5-8% less than the manufacturing cost of 4-ply.
Although the 3-ply construction exhibits significantly larger dimensional changes than the two other constructions, it appears that would not create any trouble if used as sub-flooring, since changes of moisture conditions in modern housing are not large enough to produce appreciable internal stresses.
References
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