When it comes to steel construction, if you are someone who works in construction you will no doubt already know and understand that the strength of a roof or wall system doesn’t rely solely on beams and columns.
A fundamentally crucial, but often underappreciated component, is the purlin system. Purlins are horizontal members that run across a building’s frame to provide vital support for roofing or wall sheets. It is designed to provide the ability of transferring loads safely to the primary structure.
It is also fair to say that choosing the right purlin system is a decision that can hugely influence everything from cost efficiency to durability. You have a choice of purlins available. Among the most common are Z purlins, C purlins, and Sigma purlins. If you are looking at C purlins for sale, for instance, it helps to appreciate that each option comes with its own set of advantages and limitations. It is clearly important that you know what these differences are so that you can make an informed purchasing decision.
Here is an overview of the three main types of purlin systems and their relative attributes.
Z Purlins
The clue is in their name. Z purlins are so-called for their distinctive “Z” shape when viewed from the side. This is a design that makes them one of the most extensively used systems in industrial and commercial steel buildings.
Arguably, their biggest advantage lies in their ability to overlap at joints, which allows them to span longer distances. This is a feature that makes them particularly well-suited for large construction projects such as warehouses, factories, and other wide-span structures, where minimizing the number of supports is a critical design factor.
An advantage afforded by their shape is that Z purlins also achieve a strong balance between strength and weight. They are designed to make efficient use of steel while still providing solid structural support. This can help keep material costs lower on large projects.
A notable downside to consider is that the overlapping system that gives them strength, also makes installation more complex. It is critical to note that if the joints are not aligned precisely, the performance of the entire system can be compromised.
With this in mind, this choice of purlin could be problematic when it comes to being used on smaller structures. In general, the effort required to install Z purlins may outweigh the benefits. Another issue to consider is that they can also be vulnerable to twisting under heavy loads if not properly braced.
C Purlins
Again, the clue regarding their shape lies in the name. C purlins, not surprisingly, are shaped like the letter “C” . These purlins are another popular option, particularly in residential and light commercial projects.
A key difference compared to Z purlins, is that C sections do not overlap. Instead, they connect end-to-end, which makes them easier to cut, place, and install. This is good for using in smaller buildings such as carports, garages, and sheds. Given their versatility, C purlins are often the go-to choice. Their straightforward design also means they are widely available and typically less expensive than more complex systems.
C purlins are renowned for being highly versatile. In addition to supporting roof and wall cladding, they are often used for wall framing, floor joists, and mezzanine structures.
One slight negative, is that their simplicity of design does mean there are some potential drawbacks to consider. A notable issue is that they are less efficient at covering long spans, and they require more steel to achieve the same strength as Z purlins. Also, like other open shapes, they can also twist under load if they are not braced adequately.
Having said that, overall, if you have a project where spans are short and loads are lighter, C purlins offer a cost-effective and practical solution.
Sigma purlins
Sigma purlins, get their name as a result of their resemblance to the Greek letter sigma. They are designed for strength and efficiency, and represent a more modern approach to purlin systems. Their prime advantage is that this type of purlin provides a higher load-bearing capacity while using less steel.
Not only that, their design makes them more stable under pressure, and less prone to twisting or lateral buckling. This also makes them highly capable of spanning long distances. In many cases, Sigma purlins have the ability to outperform both Z and C purlins in terms of structural efficiency.
However, the benefits of Sigma purlins do come with trade-offs. They are usually more expensive per unit than traditional shapes, and because their installation requires more precision, it requires skilled labor.
You will also discover that these purlins are also not as widely available as C or Z versions, so sourcing them can sometimes add time to a project. Despite these challenges, their combination of strength, efficiency, and stability makes them a strong choice for modern industrial buildings and large-scale projects where performance is a primary requirement.
Choosing the Right Purlin System
As you might expect, selecting the best purlin system depends on several factors. You will need to take into account a number of key factors, such as the size of the building, the loads it will carry, your budget, and the ease of installation.
Large industrial projects usually benefit from the long spans and efficiency of Z purlins, whereas smaller structures with lighter loads, often rely on the simplicity and affordability of C purlins. For cutting-edge designs or projects where weight reduction and performance are top priorities, Sigma purlins offer an advanced solution.
They might be hidden behind sheets of steel or roofing panels, but, make no mistake, purlins should be considered as the structural backbone of a building. Understanding the key differences between each type of purlin is key to choosing the right system for your project. When you make the right selection, you ensure not only the strength and durability of the building, but also achieve good long-term cost efficiency.
When it comes to steel construction, the details matter, and purlin systems are one of those fundamental details that make all the difference.