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Distance Between Floor Joists

Distance between Floor Joists

On this page, we will explain you about the distance between floor joists. You will know about what floor joists are and why they are used. The sizes, types used, and spacing options of the floor joist will be discussed also. The right spacing depends on the code requirements, the type of structure, and the weight it will bear.

There are a number of factors to consider when framing a floor:

  • A grade of the lumber.
  • Type of wood used.
  • The spacing between joists.
  • The load placed on the floor.
  • Width and thickness of the boards.
  • Length of the joists span.

Wood Species:

Different types of wood in stiffness and resistance to bending, with some species, are stronger than others types. The lumber from slow growing trees is much stronger and denser than the faster-growing trees of the same species.

  • The strength of common wood species used for framing includes:
  • High strength: southern yellow pine and douglas fir.
  • Medium strength: hemlock, spruce, and redwood.
  • Low strength: western red cedar, eastern white pine, and ponderosa pine.

Lumber Grade:

  • Higher grades of lumber or #1 are considered stronger than lower grades. The knots and other defects causing weakness to the woods. They are also much more expensive.
  • Lower grades of lumber for floor joists is graded as #2 is the most common choice for floor joists and other framing lumber. It has more knots and defects than the higher grades.
  • The lowest grades of lumber (designated as #3, utility, and #4) often have too many large knots or other defects to be used for floor joists.
  • Regardless of the grade of lumber used, try to choose straight boards which have few knots or defects with few crook along the length of the edge.

If it is possible, place any crook of the board facing up, so the weight on the joist will tend to straighten it out. The large knots found near the edge of the board should face up to the upper side, so the weak wood knot will be compressed.

Size of Lumber: It is an important factor in determining the distance a floor joist can span, playing a much larger role than the thickness. If you double the thickness or number of joists in a floor, the distance can increase by approximately 25%. When you are using the same board feet of lumber, you still could double the width of the boards that make the distance can increase between 70% to 100%.

Joist Span: You should check your local building codes before starting the construction and consult with a structural engineer.