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Floor Performance

The following list describes factors that affect floor performance and consideration of these factors may be helpful when designing a JJI-Joist floor system:

  • Deeper joists create a stiffer floor thereby reducing deflection.
  • A deep floor joist solution may in fact be cheaper than a shallow joist solution.
  • Gluing the floor deck significantly improves the floor performance, by as much as 70%.
  • A correctly nailed floor deck will improve floor performance by about 12%.
  • Thicker floor deck material will improve the floor performance.
  • Directly applied ceiling finishes will improve floor performance by about 3%.
  • Full depth blocking will improve floor performance but could lead to squeaks if not installed correctly.
  • Good quality workmanship is essential to achieve good floor performance. The provision of well prepared and level bearings, methodical erection procedure, diligent installation of all fixings and in particular fixing of the floor deck (including gluing where specified) will have a significant effect on floor performance. Gluing of the floor deck to the joists and of the tongued and grooved joints is recommended in BS7916: 1998.
  • JJI-Joist calculation sheets display a Serviceability Index. This is a measure of the joist performance (stiffness) relative to the minimum performance (12mm deflection).

In order to achieve a higher standard in floor performance James Jones & Sons Ltd have adopted a maximum deflection limit of 12mm for floors. In accordance with NHBC standards no strutting will be required using this deflection limit.

The minimum serviceability index is 1.0. The spans given in the table have a serviceability index of 1.0 but this does not include any of the beneficial effects of the various factors described above.

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