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.
to read the full article.