Floor Performance


How do you avoid floor performance problems?


Floor vibration, bounce, movement, springiness—call it anything you like, but for most homeowners, it is an unwelcome guest. A multitude of factors may cause floor performance problems. These problems are not limited to wood framing, either; steel bar joists and pre-stressed concrete floors can also experience performance problems. Unfortunately, it is not something that can be easily designed out of a floor system by following the building codes. In fact, even designing to higher deflection criteria than specified in the code (using l/480 versus l/360) does not guarantee better floor performance.

The problem with defining good floor performance is that it is highly subjective. What may be fine to one homeowner may be unacceptable to another. Trus Joist found that homeowners moving from a slab-on-grade home to a wood floor framed home were very sensitive to floor movements. Once homeowners have been sensitized to the problem, it must be virtually eliminated before they will be satisfied.

The goal is to build a floor that, from the outset, avoids the commonly-understood causes of floor performance problems.

Here are some recommendations for designing and installing wood floor systems, regardless of whether they are composed of trusses, I-joists or solid sawn lumber:

  • Design for code plus. That is, design to a higher standard than what the building codes allow. Remember that building code minimums are just that—minimums.
  • Minimize the span-to-depth (length/depth) ratio. Aim for a ratio of 20 or less. Deeper floor framing means better performance.
  • Use thick sheathing attached by glue and screws rather than nails. APA–The Engineered Wood Association provides information on sheathing and attachment.
  • Use higher quality materials and construction.
  • Properly install strongbacks in trusses.
  • Directly apply gypsum board ceilings under floor framing.
  • Use one continuous framing member over multiple supports instead of smaller pieces spanning from support to support for the same length.
  • Dampen vibrations with partition walls to running perpendicular below – and solidly attached to – the floor system.
  • Carefully install cross-bridging and blocking for I-joists and solid sawn joists. Poor installation can result in squeaking, which can contribute to the perception of bad floor performance.
  • Keep in mind that reducing on-center spacing and using concrete topping are not sure ways to improve floor performance. Also, floor framing systems supported by beams will exhibit more deflection than those supported by walls or foundations.

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