A.Howard Brickman responds: If the I-joist floor is built correctly with 3/4-inch-thick tongue-and-groove plywood, the performance of the hardwood floor will be just the same as a floor laid over a properly built dimension-lumber floor system. It doesn’t make any difference whether the I-joists are on 19.2-inch or 24-inch centers; that’s a function of the plywood. What is crucial is that you use T&G plywood, which eliminates unsupported edges.
A continuous-span wood I-joist floor, where single I-joists span from wall to wall over a center girder, has one advantage over a sawn lumber floor (where the joists typically break over the girder). The continuous span eliminates the gap that often opens in hardwood floors right over the center girder.
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