- Q. Do any I-joist manufacturers still use plywood webs? At my local lumberyard, I was told that manufacturers switched from plywood to OSB webs because the plywood tended to delaminate, but I suspect the real reason is that OSB is cheaper. I’d prefer to use plywood I-joists, because I think they’d be stronger.
A.Paul Fisette, director of Building Materials and Wood Technology at the University of Massachusetts Amherst and a JLC contributing editor, responds: While you might be able to find a small manufacturer somewhere who still makes I-joists with plywood webs, the major players do not. It may be true that OSB-web I-joists cost somewhat less to manufacture, but the main reason for the change is that OSB webs provide superior structural performance. OSB has interlocking fibers that transfer shear loads better than plywood does, making it much stronger in shear. As a result of this difference, you can cut larger holes in the OSB webs than in plywood webs, and OSB is capable of transferring greater loads to bearing points.
The OSB in I-joist webs is not the garden-variety OSB used for sheathing products. It has more wax and about 15 percent more resin, making it a very stable material. In fact, instead of being a cheaper substitute for plywood, I-joists made with OSB webs mark a significant improvement in the structural floor-framing industry.
Plywood vs. OSB I-Joists
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