bounce 05
Illustration: Ian Worpole
Building Without Bounce

The best way to limit annoying flex in a floor is to make sure that joists are sized correctly before a house or addition is built. Building codes specify the minimum joist depth and spacing (typically 12 or 16 inches on center) for spans up to 20 feet, but those requirements are intended to prevent plaster ceilings from cracking, not to eliminate springy floors. "If you build to code minimums, you most likely will have some kind of bounce," says Steve Frederickson, a registered professional engineer. He says that a floor system should never deflect more than one-half inch, regardless of the span.

Tom often goes well beyond code to meet that goal (image 5, left), framing with deeper joists, spacing them closer together, and using bridging or blocking for added stiffness. That way, he says, "the dining- room chandelier doesn't sway when the kids are jumping up and down in the bedroom."

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