Floor Joist And Wall

In building constructions the term joist refers to a horizontal framing member that is the primary structural element of a floor or ceiling frame.

Floor joist and wall.

How joists support floors and ceilings joists the horizontal members that span two walls and or beams have to carry the weight of the walls people furniture appliances and other stuff we place on them. Floor joists spaced on regular intervals span the areas between supports such as walls foundations girders and beams. When a load is applied to a joist the wood fibers along the bottom edge go into tension and those along the top go into compression fig. Both are horizontal members meaning they are installed level with the ground or floor below and both are supported on their ends and sometimes in their middles by load bearing walls columns or other types of vertical supports.

Joists are spaced at regular intervals much like the studs in a wall frame. True floor joist span calculations can only be made by a structural engineer or contractor. 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. Joists span across the tops of load bearing walls and may be supported at mid span by a beam or other member.

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