What is a Purlin in Building Construction?
If you’ve been researching metal buildings, pole barns, or pre-engineered steel structures, you may have come across the term “purlin”. It’s not the most familiar word to most buyers, but it plays a critical role in how a building performs over time.
So let’s break it down clearly: what is a purlin in building construction, what does it do, and why does it matter when you’re investing in a metal building?
What is a Purlin?
A purlin is a horizontal structural member that runs across the roof of a building. In metal buildings, purlins typically span between the main frames or rafters and provide support for the roof panels.
Think of purlins as the framework that gives the roof its strength and stability. While roof panels handle weather exposure, purlins carry the load—from the weight of the roof itself to wind, rain, and other environmental forces.
In pre-engineered metal buildings, purlins are most often made from cold-formed steel and shaped in profiles such as ‘C’ or ‘Z’ sections, depending on the building’s design and span requirements.
What Do Purlins Do?
Purlins serve several essential purposes in building construction:
1. Support the Roof System
Purlins act as the backbone of the roof. They provide continuous support for metal roofing panels, helping distribute loads evenly across the structure.
2. Improve Structural Strength
Properly engineered purlins help the building resist wind uplift, heavy rain, and other stresses common in Southern climates. Without them, roof panels would lack the support needed to perform reliably.
3. Maintain Roof Alignment
Purlins help keep roof panels straight, secure, and properly fastened over time. This reduces movement, vibration, and wear on fasteners.
4. Increase Design Flexibility
In pre-engineered metal buildings, purlin spacing and sizing can be customized based on the building’s use, such as whether it’s agricultural storage, a workshop, commercial space, or a residential metal structure.
Why are Purlins Important?
When asking “what is a purlin in building construction,” the real question behind it is usually “how does this affect my building’s quality?”
The answer: a lot.
Well-designed purlins directly impact:
Roof performance and longevity
Load-bearing capability
Resistance to wind and weather
Overall structural integrity
Cutting corners on purlin design or using materials that aren’t properly engineered can lead to roof deflection, leaks, and long-term maintenance concerns. That’s why professional design and quality materials matter.
Why Purlins Matter in Pre-Engineered Metal Buildings
In pre-engineered metal buildings, purlins aren’t an afterthought; they’re part of a complete, engineered system. Every purlin is sized, spaced, and installed according to the building’s intended use, location, and environmental demands.
This approach allows metal buildings to offer:
Efficient construction timelines
Reliable structural performance
Smart material usage
Long-term value
When buyers understand components like purlins, they’re better equipped to see the difference between a professionally engineered metal building and a one-size-fits-all approach.
Why This Matters for Your Building
Understanding what a purlin is in building construction helps you make informed decisions when planning a metal building project. It’s a behind-the-scenes component, but one that plays a major role in how your building performs year after year.
If you’re considering a pre-engineered metal building, working with an experienced team like Phoenix Building Solutions ensures every detail—from purlins to panels—is designed to do its job right. And that’s where real value is built. We provide engineer-stamped drawings with every pre-engineered building purchased, so you can rest assured that your metal home or building is well-built and safe.
Get started today by designing your own building on our free 3D design tool or by scheduling an appointment with one of our sales representatives. Not sure how to get started? Send your questions to us on our contact page. If you’re ready to start building, get your free metal building quote today.
