Decoding Bar Joists: 8 Common Questions Answered

If you plan to build a riding arena, pole barn, event venue, or other large, open building, you probably want it to be space-efficient and aesthetically pleasing. 

You also want it to be sturdy and functional! However, not every building design accomplishes all these goals. 

At Buffalo River Truss, we want to help you make your building the best it can possibly be. Today, we’d like to help by answering some common questions about bar joists, a component of sturdy, functional buildings. 

So, let’s get started! 

Table of Contents

  • What is a bar joist

    1. What is a bar joist?

  • What are bar joists made of

    2. What are bar joists made of?

  • What are bar joists used for

    3. What are bar joists used for?

  • What is the difference between a bar joist, a beam, and a standard truss

    4. What is the difference between a bar joist, a beam, and a standard truss?

  • Why use bar joists as opposed to standard trusses

    5. Why use bar joists as opposed to standard trusses?

  • How far can bar joists span

    6. How far can bar joists span?

  • What are some alternatives to bar joists

    7. What are some alternatives to bar joists?

  • What are some different styles of bar joists

    8. What are some different styles of bar joists?

8 Bar Joist FAQs

The construction world has so many terms and technicalities that learning to understand them all is a huge task!  

In this article, we will cover 8 commonly asked questions about bar joists, and by the end, you should better understand what they are, how they work, and what they are used for. 

Let’s kick it off by defining what a bar joist is.

1. What is a bar joist?

Bar joists (also called open web steel joists) are one of the structural components of buildings. In simple terms, they are beams made of a top and bottom chord, with diagonals connecting them.  

(If you want an idea for the shape, picture a long, narrow hallway. Now imagine throwing a ball really hard, at an angle, against one of the walls. It would make its way down the hallway bouncing back and forth from wall to wall. 

The two walls and the path of the ball make the shape of a bar joist: the two walls are the top and bottom chords, and the path of the ball is the diagonals connecting the two. 

Joists are used specifically for flat applications, such as to support the second floor of a house. Regular joists may simply be solid wood 2x10’s that run horizontally across a frame and support a floor. Open web steel joists, on the other hand, are made of a web of interconnected parts, making them able to support larger loads over longer distances. 

2. What are bar joists made of?

Joists may be made from wood, steel, or composite materials. Each joist is designed for the specific task it will accomplish. 

Steel is one of the most common materials because of its high strength-to-weight ratio and durability.

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3. What are bar joists used for?

Open web steel joists are used for various applications. A few of these applications include: 

  • Roof systems: These joists are widely used to support the roofs of commercial and industrial buildings, their design makes them well-suited for spanning long distances needed in large, open floor plans. 
  • Floor systems: They are often used to support the floors of multi-story buildings, especially large ones with open floor plans. 
  • Large openings in buildings: Say you want to install a 16’ door in the side of your pole barn, but your poles are spaced just 10’ apart. You could use a joist to span the distance between your poles and attach trusses to the joist instead of the poles. This enables you to build your 16’ door. 
  • Small bridges: Trusses are the best option for large bridges, but joists are suitable for spanning small distances. 
  • Mezzanines or raised platforms: They can provide the necessary support for raised platforms, both indoors and outdoors. 
  • Renovations and retrofitting: They may be used to replace older, less efficient building components and increase the strength and stability of buildings. 
  • Industrial/commercial structures: They are well-suited for spanning long distances, so they are perfect for large, open industrial buildings.  

These joists are mainly used for horizontal applications and are associated with flat roofs. However, they may also be used for sloped roofs if that is what they were designed for. 

4. What is the difference between a bar joist, a beam, and a standard truss?

Good question! Differentiating between bar joists vs. beams and bar joists vs. standard trusses can be tricky. 

Here’s the definition of each item: 

  • Beams are the simplest item. They are typically made of solid materials such as wood, concrete, or steel and span distances between two points, such as walls or posts, to support loads.  
  • Trusses are made of interconnected pieces that form triangular shapes and are specifically designed to support roofs. 
  • Bar joists are like a mix between beams and trusses. Like trusses, they are made of interconnected pieces that form triangular shapes, but they are typically used for the same sorts of applications as beams. Both beams and bar joists are used for horizontal load-bearing–however, the joists can normally support more weight because of their open-web design. 
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5. Why use bar joists as opposed to standard trusses?

The decision between different support methods depends on factors such as specific project requirements, structural considerations, architectural design, and budget. In some cases, trusses are the best option. 

However, here are a few reasons why you may want to install open web steel joists instead of standard trusses: 

  • Cost-effectiveness: They require less material and labor for fabrication, transport, and installation. That makes them more cost-effective than standard trusses for certain applications. 
  • Design flexibility: Often, construction workers find they have more flexibility to customize them to accommodate utilities, HVAC systems, and architectural features than they do with standard trusses. 
  • Quick installation: Being pre-fabricated and lighter than trusses, they are often quicker to install. 
  • Lighter weight: They are often lighter than trusses, making for simpler installation and less overall dead load on the structure.
  • Space utilization: They provide clear, wide spans that allow for maximum space usage in buildings. They also allow for better headroom. 
  • Aesthetics: They can provide a lovely open-and-airy aesthetic for event venues and other large buildings where aesthetics matter. 

There are plenty of advantages to bar joists! However, there are also certain applications where standard trusses are the better option. 

6. How far can a bar joist span?

The distance a bar joist can span depends on how it is engineered and built. Some can only span short distances, while others are engineered to span longer distances in larger buildings. 

Load capacity depends on factors including the spacing between joists, the steel gauge used, and the type of load the joists need to bear.

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At Buffalo River Truss, we have built bar joists that span up to 50 feet. Sometimes the question is not about how far the joist can span but whether or not steel joists are the most cost-effective solution for the application.

7. What are some alternatives to bar joists?

In some cases, open web steel joists aren’t the best solution, and numerous alternatives exist for these situations. 

Standard steel, concrete, or wood beams might be a better option for spanning short distances, and standard trusses may be the best choice for residential construction or other small buildings.  

More options include other types of metal trusses (we wrote a blog explaining metal trusses if you're interested), timber joists, or composite systems. Which option is best depends on the specific situation.

8. What are some different styles of bar joists?

There are plenty of different styles of joists, and they are suitable for different applications. 

A few of the different types include: 

  • K-Series joists
  • LH-Series joists
  • DLH-Series joists 
  • Joist girders

You may also need a completely custom design for your specific application. 

You may also need trusses instead of bar joists, in which case, you may want to read some of our other blogs, including:


We hope this article has helped familiarize you with open web steel joists and what they can do. 

If you are looking for steel joists or trusses for your next building project, contact us today here at Buffalo River Truss! 

We offer bar joist trusses, gable roof trusses, and pole barn trusses, as well as the best customer service possible!  

To order your joists or trusses, simply: 

  1. Contact us - We will help determine what type of truss you need.  
  2. Figure out scheduling and engineering - We’ll keep you updated on everything! 
  3. Receive your trusses - We deliver! 

Contact us today! We look forward to hearing from you! 


  1. Bob Palmer on June 27, 2024 at 8:41 pm

    I was in Sam’s Club today I noticed they have hung swimming pools, swimming pool slides , other very large swimming pool items. These items are made of thick vinal and be very heavy. All of these items were suspended from the same bar joist. My question is with this additional weight added to one single bar joist is this SAFE ? Thank you for your time in advance.

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