What Is Floor Joist

After joists are installed plywood subflooring and or drywall are fastened to the joists to complete the structural floor or ceiling.

What is floor joist.

True floor joist span calculations can only be made by a structural engineer or contractor. They are covered with subflooring panels of plywood or oriented strandboard osb to complete the floor s structural assembly and create the solid continuous platform on which you install tile carpet or other finish flooring. In buildings with basements the first level of floor joists serves the same purpose. Joists are spaced at regular intervals much like the studs in a wall frame.

This spacing is combined with a floor joist span to determine the maximum capacity load of a floor. Floor joists are an important part of the supportive structure of a floor. The floor joist is nailed to the plate material and spans the open area under the floor. In the past 2x4s or 2x6s were sometimes used as floor joists.

The floor sheeting is usually made from 3 4 or thicker sheets of plywood or osb. The rim joist fig. Considering the cross section of a typical joist the overall depth of the joist is critical in establishing a safe and stable floor or ceiling system. In many countries the fabrication and installation of all framing members including joists must meet building code standards.

Floor joists installed on second or third or higher levels double as ceiling joists for the level below. Joists must exhibit the strength to support the anticipated load over a long period of time. This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction. Floor joist spacing is the distance a floor joist board can be separated from an adjacent floor joist.

Joists span across the tops of load bearing walls and may be supported at mid span by a beam or other member. Each type of wood has a specific span and spacing requirement. The width of a board is an important factor in determining the distance a floor joist can span playing a much larger role than the thickness. This size is no longer acceptable when framing a structure.

For example if you double the thickness or number of joists in a floor the distance the boards can span will increase by approximately 25. In building constructions the term joist refers to a horizontal framing member that is the primary structural element of a floor or ceiling frame.