Q&A: Floor Stiffness: I-Beams vs. Solid Lumber

A.Wood I-beams are actually stiffer than dimensional lumber of a comparable size. But you have to distinguish between “bounce” and “vibration.” Because wood I-beams are lighter, they tend to vibrate more easily, giving the floor a hollow feel. This generally won’t be a problem if a drywall ceiling is installed below the floor. If the floor is open below, install strapping to the bottom of the joists on 6-foot centers to reduce the vibration.

To reduce bounce, select wood I-beams for an allowable deflection of 1:360, not 1:240. If you are building for a greater anticipated load than normal (a water bed, a grand piano), go to the next deeper joist than required by the design tables.

Another trick is to build in the china cabinet at or near a bearing wall, rather than out in the middle of a span. Nothing will convince a customer he has a bouncy floor more than the crystal in an overcrowded hutch ringing like the Bells of St. Mary’s.