What Are the Different Types of Joist Design?

Andrew Kirmayer

Joists are structural components of buildings and other structures. They often support loads as well as provide aesthetic appeal. There are various kinds of joist design depending on the kind of structure and what an architect or engineer finds to be the most appropriate. Designs include the web structure of a bar joist, and building framing can also be made of wood or steel. These structural elements can also be built into the ceiling or a floor, or be exposed to provide a particular motif for the interior appearance of a building.

View of second story floor joists from below.
View of second story floor joists from below.

Many types of joist design use one material. Bar joists typically include both supports and chords in a kind of truss-like structure. They can be used in almost any type of structure, including residential apartments and commercial office buildings. Industrial complexes, hospitals, bridges, and even stadiums often use these components as well. These joists distribute the load of a floor or roof to the walls or the foundation of a structure, and their design usually depends on the type of building.

Floor joists on new construction.
Floor joists on new construction.

A wood joist design is sometimes used if the load can be supported by a timber frame. Often added when building houses, these are sometimes decorative as well as essential to structural integrity. Steel joists are generally more suitable for the structural engineering of large buildings and bridges. Sometimes built into floors and ceilings, these can include lightweight composite materials for supporting heavy loads in a compact space. Such elements are occasionally built to support varying forces and to be flexible.

Some structures are better off with joists in the ceiling, while others have a floor joist design. Floor boards often cover the structural components and can add stability when multiple joists are connected. In addition to being load bearing, exposed joists can also be used for interior design. Even 21st century interior decorators sometimes use them to create a feel of the past.

Another component of joist design is the overall support system. The structural supports can be held in place at both ends. They can also be connected at one end or be free standing at the other, which is known as a cantilever joist design. Architects and engineers are usually most qualified for determining which design to use. There are also tools online, such as a joist calculator, which can help determine the best design depending on the material, size, and how much space is between the joists.

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