Floor vibration, or bounce, is not a safety issue — it's a performance issue, and one that's likely to be important to homeowners. No one likes to hear the china rattling in the cabinet when they walk across the room. But at what point is the floor stiff enough, and how can a builder predict how the floor will perform? Unfortunately, there's no clear-cut rule for a builder to follow, and the physics of vibration are so complicated that it's no easy matter to design a guaranteed bounce-free floor (see "Sizing Stiff Floor Girders," Practical Engineering, 8/97). Also, "acceptable" floor performance is highly subjective: What's good enough for one homeowner may not be good enough for another. The building
