What is the term for the horizontal framing member that supports the floor?

The correct term for the horizontal framing member that supports the floor is a joist. Joists are essential components in the floor framing system; they are typically made of wood or metal and run parallel to each other to form a framework. These members bear the weight of the floor above and distribute it to the walls or beams below, providing both support and structural integrity.

In a typical floor assembly, joists are spaced evenly apart to create a uniform surface that can accommodate flooring materials. Their design and placement are critical to ensuring that the floor system is sturdy and capable of handling live loads (the weight of people and furniture) as well as dead loads (the weight of the materials themselves).

While beams, trusses, and rafters are all important elements in building construction, they serve different functions. Beams are larger horizontal members that typically support joists or other structural loads. Trusses are triangular frameworks used primarily in roofs to distribute loads over a wider area. Rafters are sloped members that support the roof covering and are also part of the roof framing system. Understanding these distinctions helps clarify why a joist specifically refers to the horizontal support for floors.