How to Use a Uniform Load Span Chart for Floor Joists

When building a house, it is a good idea to get informed about the building materials you will be using. This is especially important when considering floor joists. Because the joists can support not just the floor but also the ceiling of the floor below, load bearing capacities must be considered. Uniform load span charts have valuable information, but can be a little tricky to understand.

  1. Remember that there are three classifications for loading on a floor system. They include top-live, top-dead and bottom-dead. For example, a loading of 45 psf, or pounds per square foot, will be 30 psf top-live, 10 psf top-dead and 5 psf bottom-dead--or 30-10-5. This information will help you make better use of a uniform load span chart for floor joists.

  2. Use the designation "dead loads" when referring to the weight of such building materials as subfloor, flooring tile, sheetrock, joists and more. Top-load refers to the flooring material that can be above the joist, and bottom-load refers to the Sheetrock for the ceiling below the joist. You can use the uniform load span chart cam help you decide the appropriate thickness and strength of the floor joists according to the materials you plan to use for your ceiling and your floor as well as the span the joist must stretch.

  3. Consider that "live loads" can mean snow, wind or even people. Building codes require floor systems to withstand more than they will face in everyday life, just so the fluctuation that can happen with live loads will be covered.

  4. Take in consideration stiffness ratios. You will find these ratios listed with an "L" before it when you use the uniform load span chart for floor joists. This number is important because it tells you how stiff the joist will be as it spans a distance in a building. Generally speaking, the higher the number, the better. An L/715 floor is stiffer than an L/315 floor. Code dictates that the joist stiffness should be at least L/360.

  5. Look for camber or crown when considering floor joists. This information may not be found when you use uniform load span charts for floor joists, but is worth inquiring after when in the market for floor joists. The camber refers to a slight upward curve of the joist, which is helpful to compensate for dead loads. Over time, dead loads can cause the floor joists to straighten. If the floor joists have no camber, they can curve downward over time.

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