What Is a Metal Joist?

M. McGee

A metal joist is a structural component found in buildings and is generally made of steel. These bars connect structural beams to each other or to other load-bearing objects. In wooden buildings, these beams typically support the majority of floors and ceilings and are mostly or completely covered in all but basements or attics. In most cases, a metal joist is found on larger structures, primarily warehouse-style buildings or other similar structures. In this case, the joists are often visible near the ceiling.

Woman holding a book
Woman holding a book

Joists are a very common part of nearly every complex structure. Most buildings are designed with a handful of beams and load-bearing structures. These create a frame that the rest of the building is built within. The beams are usually quite far apart, often making up only the major portions of a building or room. This usually means that only the corners and major intersections of a building contain actual load-bearing segments.

Between the various supporting structures are joists. These don’t actually hold up walls or floors, but they allow the walls and floors to maintain a shape. A joist is usually smaller than a beam and there are a lot more of them within a wall. They will connect important structural supports to other parts of the building or to one another to improve the usefulness of the beams. These inner structures give the areas of a building rigidity between the load-bearing parts and support inner finishing, such as drywall, window and door frames.

In the majority of houses and other residential or light commercial structures, these joists are made of wood. In heavy commercial, industrial or metal structures, it is more common to use a metal joist or no joist at all. Some buildings of this type forgo joists completely in favor of reinforced concrete. In this case, the concrete contains a metal grid that gives the material inner solidity, removing the need for a metal joist.

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The one form of structure where one can always find a metal joist is in large, open and metallic structures. Buildings such as warehouses, large, open department stores, airplane hangars and similar buildings will nearly always use metal joists in the ceiling of the building. In most cases, these large, open buildings have hundreds of these joists visible within the larger support structure. These joists often appear as simple metal rods that connect the very large support beams to the smaller beams that hold up the ceiling and the walls.

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