Beam floor in new construction.
A floor joist is a large beam, usually steel, that spans the width of a house in the center and supports the floor joists. The floor joist is commonly used in houses that have a basement. The joist is generally supported along its entire length with adjustable jacks that rest on cement pads and adjust upward to protect the joist from the ground and prevent sagging. With the advent of the manufactured particleboard beam, some builders are choosing to forego the steel beam for the manufactured wood product. An advantage of using the steel beam is that it has less tendency to twist and sag than a similar sized wooden beam.
An I-beam, which is commonly used for flooring.
The open space of a basement forces the builder to take steps to prevent the floor from sagging as the joists cover the opening without any support. With all the materials used by builders to prevent this from happening, nothing is as successful at supporting a floor as a floor joist. Typically formed from a steel “I” beam, the floor beam rests on notches built into the house foundation at each end. The length of the joist will determine how many floor jacks will be needed to support the length of the joist.
The floor joist itself is commonly hidden by the ceiling boards of a finished basement, while the connectors are usually boxed in and blended into the surrounding area through paint, paneling, or wallpaper. In an unfinished basement, the joist and outlets are often exposed. When using steel floor joists, some builders apply a bead of epoxy or strong glue under the floor joists to prevent them from slipping on the steel surface. In a wooden beam, the joists are commonly nailed to the beam to prevent noise and slippage.
It is common for a builder to use a floor joist only on the first floor of a building and rely on interior walls and other interior features to support any subsequent upper floors. Some construction projects, especially those that incorporate a large open space or loft-style upper floor, can often use a large wood floor joist to add architectural strength and visual appeal to the structure. Buildings such as log houses are often designed with large wooden beams that span the width of the upper stories, including the roof, to provide needed support without sacrificing traditional visual appeal.