What Is Floor Joist

The floor joist is nailed to the plate material and spans the open area under the floor.

What is 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. They hold up the weight of a building absorb impacts on the floor and create structural support so that the floor will be stable and secure. Floor joists are an important part of the supportive structure of a floor.

This spacing is combined with a floor joist span to determine the maximum capacity load of a floor. Joists are spaced at regular intervals much like the studs in a wall frame. Joists must exhibit the strength to support the anticipated load over a long period of time. In building constructions the term joist refers to a horizontal framing member that is the primary structural element of a floor or ceiling frame.

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. The floor sheeting is usually made from 3 4 or thicker sheets of plywood or osb. The floor sheeting is also engineered to provide a solid floor. 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 the past 2x4s or 2x6s were sometimes used as floor joists. B the framing member that runs around the perimeter of your house and that the floor joists butt into often gets riddled with large holes this space is the logical exit point for dryer and furnace vents big electrical service wires and fireplace fresh air intakes. In many countries the fabrication and installation of all framing members including joists must meet building code standards. True floor joist span calculations can only be made by a structural engineer or contractor.

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. This size is no longer acceptable when framing a structure. 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. After joists are installed plywood subflooring and or drywall are fastened to the joists to complete the structural floor or ceiling.

In buildings with basements the first level of floor joists serves the same purpose. The rim joist fig.