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Joists vs. Beams: Understanding The Structural Differences
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Joists vs. Beams: Understanding The Structural Differences

Posted on October 27, 2023

Estimated Reading Time : 6 Min.

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Joists vs. Beams: Understanding The Structural Differences

Have you ever wondered about the fundamental components that hold a building together? Joists and beams are two essential elements in the construction world, each with a unique role in ensuring the stability and strength of a structure. While they might seem similar at first glance, their differences are crucial to understand before starting a construction project. In this blog post, we’ll explore the differences between joists and beams, shedding light on their distinct functions, materials, and applications. By the end, you’ll have a clear understanding of when to use joists and when to opt for beams, empowering you to make informed decisions in your construction endeavors.

Joists vs. Beams: How Do They Work?


Joists are horizontal structural members that play a critical role in supporting the floors and ceilings of buildings. This is why they’re typically called ceiling joists or floor joists. Joists are typically smaller and shallower in size compared to beams, making them easier to handle and install.

Joists provide structure by spanning the open areas between beams or load bearing walls, to evenly spread the weight of the ceiling or floor. Joists are often installed closely together to maintain the structural integrity of the floor or ceiling system.

The material composition of joists can vary, commonly being constructed from wood, steel, or engineered wood. Depending on the material, they exhibit different load bearing capacities. Joists may exhibit some deflection or flex under heavy loads due to their smaller size and spacing. This flexing allows them to adapt to various loads and distribute them without compromising the structural stability of the building.


Beams, on the other hand, are versatile structural elements with horizontal or vertical orientations. They are designed to bear heavier loads over longer spans. Beams can have various shapes, such as I-beams or H-beams, and are typically larger and deeper than joists.

Beams work by concentrating loads at specific points, often transferring these loads to columns or load bearing walls. Due to their larger size and load-bearing capacity, they are suited to support upper floors and roofs. Beams are essential components in various applications, including bridges and framework systems.

In contrast to joists, beams aim to minimize deflection or flex. They are engineered to resist bending and provide rigid support for the structures above. Beams are commonly constructed from materials like steel, concrete, or wood, depending on the specific requirements of the building.

Joists work by evenly distributing loads across a wide area, providing support for floors and ceilings. Beams, on the other hand, concentrate loads at specific points and offer robust support for upper floors and other structural elements, minimizing deflection to ensure stability. Both joists and beams are crucial components in construction, each tailored to its distinct role.

Below is a chart to help you get a clearer picture of the differences between the two. 

Joists vs. Beams: Structural Differences

Function Support the floor and ceiling of structuresCan be horizontal or vertical    
OrientationTypically horizontal           Can be horizontal or vertical      
Span CapabilityShorter spans compared to beams   Longer spans, providing more support
Load Distribution  Distribute loads across a wide areaConcentrate loads at specific points 
Cross-Section    Rectangular or I-shaped              Various shapes, e.g., I-beams, H-beams
Position  Placed perpendicular to the beams Often run parallel to the floor     
Size and DepthSmaller and shallower Larger and deeper    
Materials   Often made of wood, steel, or engineered wood Commonly steel, concrete, or wood
Usage in Construction   Found in the framework of floors and ceilings Used in framework and overall roof support
Load-Bearing CapacityLower load bearing capacity compared to beamsHigher load bearing capacity       
Deflection Tolerance May have more deflection or flex under certain weightMinimal deflection, designed to resist bending
InstallationEasier to install due to lighter weight and smaller sizeMay require heavier machinery for placement
Cost    Generally more cost effective  Often more expensive due to greater strength
Spacing         Closer spacing between joists      Wider spacing between beams    

Joist vs. Beam: Types

As mentioned in the chart, joists and beams come in different variations. Let’s explore these different types:


Types of Joists:

  1. Floor Joists: As the name suggests, floor joists support the floor of a home. They run the length of the structure and are typically covered with plywood that makes up the base of the floor. Floor joists can be accessed through basements or crawl spaces and should be inspected occasionally for damage and rot.
  2. Ceiling Joists: The opposite of floor joists, ceiling joists are used to support the weight of the roof. They are parallel to the purlins, but are lower in the roof structure, and attach to the top of the wall plates. 
  3. Rim Joists: Working together with ceiling joists, rim joists support the roof. These joists create the perimeter of the buildings’ structure and attach to ceiling or floor joists to prevent them from buckling. Rim joists also provide an outside edge for the sheathing to be nailed over the rafters or trusses. 
  4. Deck Joists: These components create the framework of an outdoor deck. The size of the joists and the amount needed depends on the desired length and width of the deck itself. 

Types of Beams:

1. I-Beam:

Shaped like the letter “I”, this beam provides excellent strength while minimizing the weight of the material. It’s commonly used in the construction of buildings and bridges.

2. H-Beam:

Resembling the letter H, H-beams are often used in the construction of large structures, providing strong support in multiple directions.

3. Cantilever Beam:

This type of beam is anchored at one end and extends freely into space. It’s used in structures like balconies.

4. Box Beam:

A box beam is a closed rectangular structure, providing a higher resistance to movement. It’s frequently used in the framework of a roofing system.

5. Composite Beam:

Composite beams combine materials like steel and concrete to enhance strength and load-bearing capacity.

6. T-Beam:

Shaped like the letter T, these beams are commonly used in the construction of slabs and walls.

7. Channel Beam:

Resembling the letter C, channel beams are often used for support in frames and trailers.

8. Laminated Veneer Lumber (LVL):

LVL beams consist of layers of veneer glued together, providing superior strength and stability.

9. Glulam Beam:

Glulam beams are constructed by gluing multiple layers of timber together, offering high strength and resistance to warping.

These various types of joists and beams are integral to construction and woodworking, each serving unique purposes based on the specific requirements of a project. The choice of joist or beam depends on factors such as load bearing capacity, materials, aesthetics, and the intended application in structural or woodworking projects.


Joist vs. Beam: Cost Comparision

When comparing the cost of joists and beams, it’s important to consider several factors that influence the overall expense of these structural elements.


Cost considerations for joists include:

1. Type of Joist: The cost of joists depends on what type you are installing, whether floor, ceiling, or rim joists. Ceiling joists are more expensive, whereas floor joists usually cost less overall. 

2. Material Cost: The cost of materials for joists varies depending on the material used, but in general, steel joists are often more budget friendly than wood.

3. Labor Costs: The total cost of labor for joist installation or repair will depend on the local rates in your area, the size of the project, and the material you choose. You can typically expect to pay $50 to $100 per hour. 


Beams can have a wider price range, influenced by various factors:

1. Material Cost: The average cost of a steel I-beam typically ranges from $0.90 to $1.60 per pound for materials. The material cost can vary significantly based on the size and type of beam required for the project.

2. Labor Cost: Labor costs for beams may be higher compared to joists due to the need to build the beam and perform additional structural work.

3. Permit Costs: Depending on the location and the complexity of the project, the cost of permits to build can add to the overall expense.

In addition to the aspects of cost mentioned above, it’s essential to recognize that steel joists, while slightly more expensive than traditional timber, offer advantages such as a lightweight construction, which makes them easier to handle and install. Mild steel beams are another cost effective option when compared to solid wood beams, offering both durability and affordability.


Understanding the structural differences between joists and beams is essential for successful construction projects. Joists provide even support for floors and ceilings, while beams bear the weight of upper floors and other structural elements of the roofing system. Choosing the right option depends on factors such as load-bearing capacity, materials, and project requirements. 

If something is wrong with the structure of your roof, or you want a new one installed, you need the best roofing services in Dayton, OH. At All Around Roofing, Siding & Gutters, we offer top notch roofing services to Kettering, Englewood, and the surrounding areas of Ohio.  Give us a call at (937) 902-2839 for expert assistance. Your project deserves the quality and reliability we provide.

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