Steel Purlins

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  Have you ever looked up at the interior of a steel structure and wondered, "What are those bars supporting the roof called?" If so, you’ve come to the right place to find your answer.

  
  

  The answer to this question, of course, is the title of this blog: purlins. These critical components are what quite literally keep the roof over your head. Purlins are fundamental to the structural integrity of most buildings, playing a vital role in ensuring stability and durability. They are a mark of quality in steel building structures, often overlooked but absolutely essential.

  
  

  In this article, we will delve into the role purlins play in maintaining the integrity of your steel building. By understanding the importance of purlins, you'll be better equipped to make informed decisions when it comes to purchasing materials for your next building project. Proper structural integrity and load support are key to the longevity of any building and the safety of its occupants.

  
  

  We will explore various aspects of purlins, including why your building might need them, the different materials they can be made from, and the various shapes they can take. Each of these factors can significantly influence the performance and durability of your building structure.

  
  

  Understanding whether your building requires purlins, what material they should be made of, and what shape they should take are crucial questions you should answer before constructing a new structure. So, let’s dive in and explore the world of purlins, ensuring that your next building project stands the test of time and provides a safe, reliable environment for all its occupants.

  
  

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  What are Purlins?

  Found in most large structures, purlins are the horizontal beams that provide structural support to a building by helping to transfer roof loads to other major structural elements. In other words, they support the weight of the metal sheeting, plywood, wooden panels, and other materials that comprise the surface of a roof, as well as anything else that might accumulate on top of a roof, such as snow, water, or building accessories.

  
  

  While the specifics can vary from structure to structure, purlins typically help distribute the load of a roof to other structural elements like building walls, rafters, or metal support beams. This distribution helps diffuse the weight of a building’s roof across the entire surface and multiple components of the building, rather than concentrating the load on just the walls, rafters, or other singular elements. Essentially, purlins are necessary components for ensuring the quality and longevity of a building. Regardless of whether your structure is made from wood, steel, or another material, purlins play a critical role in maintaining the structural integrity of any roof. The number of purlins a roof has, as well as their thickness or depth, varies depending on the load requirements for that specific building.

  
  

  Purlins come in various forms and are typically classified according to their shape, the material they are made from, and their intended use.

  
  

  While we will discuss the different purlin shapes shortly, it's important to note that, when it comes to material, steel purlins are the preferred choice within the construction industry. Unlike wood, steel purlins do not rot, are unaffected by water and moisture, and exhibit minimal expansion and contraction in different climates. These are all weaknesses of wooden purlins, which can seriously hinder the structural integrity of a roof and, consequently, the structure itself.

  
  

  Steel purlins are typically made from cold-formed steel. Unlike hot-formed steel, cold-formed steel is produced by rolling and pressing thin sheets of steel into the desired shape. This process results in steel that is stronger and easier to work with compared to hot-formed steel. Once formed, the steel is then dipped in molten zinc in a process known as galvanizing. Galvanizing coats the steel in zinc, protecting it from harsh environments and corrosion. Galvanized steel can often be identified by its distinctive ‘spangle’, a crystallized pattern on its surface.

  
  

  Purlins make up the secondary support system in the framing of a building, working alongside their horizontal counterparts, girts. Girts and purlins run between the primary framing elements, much like cross beams in a wooden structure. The purpose of these secondary structural supports is to distribute loads onto the primary framing and foundation. Additionally, the secondary framing is used to attach wall cladding and the roof, providing further stability and support to the entire structure.

  
  

  Understanding the role of purlins in your building project is crucial for making informed decisions that ensure the safety, durability, and longevity of the structure. Whether you are constructing a new building or upgrading an existing one, considering the type and quality of purlins used can significantly impact the overall performance and lifespan of the building.

  
  

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  Why Purlins Are Used in Metal Buildings

  While we now understand what purlins are, it’s essential to reinforce the reasons why they are used. Purlins significantly contribute to the structural integrity of a building’s roof by running perpendicular to the rafter beams (see adjacent image).

  Enhanced Load Distribution

  One of the primary reasons for using purlins in metal buildings is their ability to enhance load distribution. By transferring the weight of the roof sheeting and any additional loads (such as snow or maintenance equipment) to the rafters and other structural elements, purlins help ensure that no single component bears excessive stress. This distribution of load helps prevent structural failure and prolongs the lifespan of the building.

  Increased Structural Stability

  Purlins provide additional points of support across the roof span, which increases the overall stability of the structure. This added stability is particularly crucial in regions prone to high winds, heavy snowfalls, or seismic activity, as purlins help the building withstand these forces without compromising the roof's integrity.

  Flexibility in Design

  The use of purlins allows for greater flexibility in the design and construction of metal buildings. By incorporating purlins, architects and engineers can design roofs with longer spans and fewer supports, creating more open interior spaces without the need for additional columns or load-bearing walls. This flexibility is advantageous in applications such as warehouses, industrial buildings, and large commercial spaces where open floor plans are desired.

  Cost-Effectiveness

  Purlins are a cost-effective solution for reinforcing the roof structure. By providing additional support and reducing the need for extensive structural elements, purlins can help lower material costs and labor expenses during construction. Their lightweight nature also simplifies transportation and handling, further reducing overall project costs.

  Ease of Installation

  Steel purlins, in particular, are known for their ease of installation. Manufactured in standard sizes and shapes, they can be quickly and efficiently installed, saving time and labor during the construction process. This ease of installation translates to faster project completion times and reduced disruption to ongoing operations.

  Durability and Low Maintenance

  Steel purlins offer exceptional durability and require minimal maintenance. Unlike wooden purlins, steel purlins are resistant to rot, pests, and moisture, ensuring they maintain their structural integrity over time. Additionally, galvanized steel purlins are protected against corrosion, making them suitable for use in various environmental conditions without the need for frequent maintenance or replacement.

  Compatibility with Modern Building Systems

  Purlins are compatible with modern building systems and materials, including advanced insulation and roofing systems. This compatibility allows for the integration of energy-efficient and sustainable building practices, such as the installation of solar panels or green roofs, further enhancing the building’s performance and environmental footprint.

  In summary, purlins are used in metal buildings for their ability to enhance load distribution, increase structural stability, provide design flexibility, offer cost-effective reinforcement, simplify installation, ensure durability with low maintenance, and integrate seamlessly with modern building systems. Understanding these benefits underscores the importance of incorporating purlins into your building project to achieve a robust, efficient, and long-lasting structure.

  So why are purlins used in metal buildings? There are 3 structural functions provided by purlins for metal roofing.

  • Purlins tie the rafters together, which stabilizes and reinforces the frame.
  • Purlins provide additional support between the spans of the separate framing bays,
  • Purlins improve the roof’s resistance to excessive rain, snowfall, and any other temporary loads that might be exerted on the roof.

  
  

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  Spacing, Spans, and Laps

  Before installing purlins, it's important to familiarize yourself with three key terms: purlin spacing, purlin span, and purlin laps. Understanding these concepts is crucial for ensuring the proper installation and structural integrity of your roof. Let’s define and examine each of these below:

  Purlin Spacing

  Purlin spacing refers to the amount of space between each purlin as you move down the side of the roof. The sections of purlins follow the slope of the roof they support. The number of purlins and the space between each one are determined by several factors, including the size, weight, and specific requirements of your building. Proper spacing ensures that the roof load is evenly distributed and that the purlins provide adequate support.

  Purlin Span

  Purlin span is the distance between the centers of the bolts on each end of an individual purlin. It's important to note that the span does not refer to the length from one end of the roof to the other, but rather the length between the ends of a single purlin. In most cases, the width of your roof will require multiple purlins and spans to fully support it. The span of each purlin is critical for determining how much weight it can carry and how effectively it will distribute the load.

  Purlin Laps

  Purlin laps refer to the overlap between individual purlins. In wide structures, it may be necessary for multiple purlins to overlap to ensure continuous support. The general recommendation for purlin laps is that they should make up 15% of the span. For example, if a purlin span is 20 feet, the lap should be 3 feet. At the midway point of each lap (i.e., 7.5% of the span), the two overlapping purlins should be bolted to the primary structure. This bolting provides additional stability and ensures that the purlins work together to support the roof.

  Diagram Explanation

  While a diagram is not provided here, visualizing the locations of purlin spans, spacing, and laps can greatly aid in understanding these concepts. Typically, a diagram would show the slope of the roof with horizontal lines representing the purlins. Vertical lines or measurements would indicate the spacing between each purlin. The spans would be marked between the center points of bolts at each end of the purlins, and the laps would show the overlapping sections where bolts secure the purlins to the primary structure.

  Importance of Understanding These Terms

  Grasping these terms is crucial for the proper installation of purlins on the roof of your steel building. Accurate spacing, span, and lap measurements ensure that the roof structure is stable, resilient, and capable of handling various loads, such as snow, rain, and other environmental factors. Incorrect installation can lead to structural weaknesses, potentially compromising the safety and longevity of the building.

  Conclusion

  In summary, understanding purlin spacing, span, and laps is essential for anyone involved in the construction or maintenance of metal buildings. These terms define how purlins are arranged and connected, directly impacting the structural performance of the roof. By ensuring proper installation based on these concepts, you can achieve a strong, durable, and safe roofing system for your steel building.

  
  

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  What Are the Different Types of Purlins?

  We know that steel as a material is a better pick when it comes to important structural elements of a building, like purlins, but let’s also examine the different options that exist for purlin shape.

  
  

  C-Shaped Purlins

  As the name implies, C-shaped purlins take the shape of the letter C and are crucial for reinforcing the structural integrity of roofing systems. In some construction projects, C-shaped purlins can be utilized as support beams in flooring systems. However, in the context of pre-engineered steel building constructions, they are primarily used in roofing systems.

  Versatility in Design

  C-shaped purlins come in a variety of lengths and thicknesses, allowing them to be tailored to meet the specific requirements of a given project. This versatility makes them a popular choice for a wide range of building applications, as they can be designed to fit any structural need. Their adaptability ensures that they can be easily incorporated into various roof designs and configurations.

  Applications in Smaller Structures

  While versatile, C-shaped purlins are not as sturdy as some other types of purlins, such as Z-shaped purlins, which we’ll discuss next. Due to this relative lack of sturdiness, C-shaped purlins are typically used in smaller structures and building projects where the demands on the roofing system are not as intense. Their use is ideal for smaller, less demanding applications where the structural loads are moderate and do not require the added strength provided by other purlin types.

  Benefits and Limitations

  • Benefits:

  • Ease of Installation: C-shaped purlins are relatively easy to install, making them a convenient choice for construction projects.
  • Customizable: Available in different lengths and thicknesses, they can be customized to suit specific project requirements.
  • Cost-Effective: Often more affordable than heavier-duty purlins, C-shaped purlins provide a cost-effective solution for smaller structures.

  • Limitations:

  • Strength: C-shaped purlins are less sturdy compared to other purlin types, limiting their use to smaller structures.
  • Load Capacity: They may not be suitable for roofs that need to support heavy loads, such as significant snowfall or large mechanical equipment.

  Conclusion

  In summary, C-shaped purlins are an essential component for reinforcing the roofing systems of smaller buildings. Their versatility, ease of installation, and cost-effectiveness make them a valuable choice for a variety of construction projects. However, their relative lack of strength compared to other purlin types means they are best suited for smaller structures where the demands on the roofing system are moderate. Understanding the specific needs of your project will help determine whether C-shaped purlins are the right choice for your construction needs.

  
  

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  Z-Shaped Purlins

  Z-shaped purlins, thanks to their distinctive shape, offer greater strength compared to C-shaped purlins. Their Z-shape allows them to overlap at joints, providing superior support and stability. This characteristic makes Z-purlins the preferred choice for supporting the roofing of larger buildings where enhanced strength and support are crucial.

  Overlapping Joint for Enhanced Support

  One of the key advantages of Z-shaped purlins is their ability to overlap at joints. This overlapping feature significantly increases the overall structural integrity and load-bearing capacity of the roofing system. The overlap ensures that there is a continuous support system across the roof, distributing loads more effectively and minimizing stress on individual purlins.

  Applications in Larger Buildings

  Due to their superior strength, Z-purlins are commonly used in larger building projects where robust support is essential. These purlins sit between the building and the roofing sheets, acting as a strong support system to ensure that the roofing sheets are attached firmly and securely. This makes them ideal for larger structures such as industrial buildings, warehouses, and commercial facilities, where the roofing system needs to withstand substantial loads and environmental stresses.

  Customizability and Ease of Installation

  Like C-shaped purlins, Z-shaped purlins can be manufactured to meet nearly any length or thickness requirement. This customization ensures that they can be tailored to the specific needs of a project, providing optimal support and stability.

  Additionally, both C- and Z-shaped purlins come pre-drilled and ready to use, which simplifies the installation process. The pre-drilled holes ensure precise and efficient installation, reducing labor time and costs while enhancing the overall construction process.

  Benefits and Limitations

  • Benefits:

  • Enhanced Strength: The Z-shape and overlapping joints provide superior strength and support, making Z-purlins ideal for larger buildings.
  • Customizable: Available in various lengths and thicknesses to meet specific project needs.
  • Pre-Drilled: Ease of installation with pre-drilled holes, ensuring accuracy and efficiency.
  • Improved Load Distribution: Overlapping joints help in distributing loads more effectively across the roofing system.

  • Limitations:

  • Cost: Due to their enhanced strength and features, Z-purlins may be more expensive compared to C-purlins.
  • Complexity: The overlapping joints, while beneficial for strength, may add complexity to the installation process compared to simpler purlin designs.

  Conclusion

  In summary, Z-shaped purlins are a vital component for the roofing systems of larger buildings. Their unique shape and ability to overlap at joints provide superior strength and support, making them suitable for structures that require robust and reliable roofing support. The customization options and ease of installation further enhance their appeal for various construction projects. Understanding the specific requirements of your building project will help determine whether Z-shaped purlins are the optimal choice for ensuring a strong, durable, and stable roofing system.

  
  

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  Handling and Storage

  Before your building materials arrive, it's crucial to plan the storage location for your purlins. Purlins should be stored in a dry place to prevent water accumulation, which can lead to premature corrosion and delay building schedules. When you’re ready to start attaching your purlins, remember not to cut or alter them during assembly. Purlins are specifically designed with the structure and load-bearing requirements in mind. Altering them could compromise their structural integrity and diminish the functionality of the secondary framing system.

  Installation Tips

  • Horizontal Installation: Purlins are installed horizontally under metal roofs, similar to metal roofing installation.
  • Bolting Preferred: Purlins should be bolted on rather than welded. Welding can affect the cold-formed steel, introduce stress to the connections, and damage the protective coating, leading to premature corrosion and reduced durability.

  5 Strengths of Steel Purlin Roofing

  Now that you have a clear understanding of what purlins are and their importance, let's explore the top five reasons why steel purlins are a no-brainer for your next building project:

  1. Ideal for Different Structures

  Steel purlins are suitable for all types of structures, making them ideal for almost any building project. Pre-engineered buildings are popular among both professionals and DIY builders. Steel purlins can be pre-cut and pre-drilled before arriving at your build site, making them an ideal choice for prefab steel building kits. This preparation ensures easy installation, saving time and effort.

  2. Provide Roofing Support

  Purlins are integral to roofing support, literally keeping the roof over your head. A quality roof, supported by purlins, protects the building from weather conditions, impacts, and moisture, and improves insulation. Proper support from steel purlins ensures the roof remains durable and effective for decades.

  3. Non-Combustible

  Unlike wooden components, steel purlins are non-combustible. Steel does not ignite or burn, providing a significant safety advantage over wood. In the event of a fire, steel purlins help contain or slow the blaze, offering better protection for the building and its occupants.

  4. Lightweight

  Steel purlins are lightweight, making them easy to handle and assemble. The innovative design, particularly of Z-shaped purlins, allows them to be thin and lightweight without sacrificing strength. Additionally, the thin design means less steel material is needed, translating to cost savings for the customer.

  5. Longevity

  Steel purlins have an incredibly long lifespan, often lasting upwards of 50 years with minimal maintenance. Because they aren’t directly exposed to the elements, maintenance requirements are low, ensuring they remain a durable and reliable component of the building for decades.

  Conclusion

  Well, there you have it – you’re a purlin expert! You now understand what purlins are, why they’re crucial to the structural integrity of a building, and the common forms they take. If you’re considering new building construction, partnering with a reputable construction company is essential. Norsteel Buildings has been providing quality steel buildings to clients for nearly thirty years. When you partner with us, you are assigned a steel building expert who acts as your personal consultant and resource throughout the construction process.

  
  

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