Barndominiums have taken rural and suburban America by storm, offering a modern blend of practicality, open space, and durability. While the aesthetics and cost-efficiency of barndominiums often take center stage, the real engineering magic lies beneath the surface—especially in the steel skeleton that gives these structures their strength. Two critical elements that play a major role in barndominium stability are girts and purlins.
These horizontal members may not be as flashy as exterior finishes or interior design choices, but they are absolutely essential to the structural integrity and longevity of any metal building. In this blog post, we’ll explore what girts and purlins are, how they function, and why they are non-negotiable for a safe, long-lasting barndominium.
What Are Girts and Purlins?
Before diving into their role in stability, let’s define what girts and purlins actually are.
- Girts are horizontal structural members attached to the vertical steel columns (or posts) of a metal building’s wall frame. They support the wall panels and help distribute wind loads across the surface.
- Purlins are the horizontal supports that run perpendicular to the roof trusses or rafters. They support the roofing panels and help resist loads such as snow, wind uplift, and even foot traffic during installation or maintenance.
Both girts and purlins are usually made of cold-formed steel, typically in a “C” or “Z” shape, which gives them high strength-to-weight ratios. These components form the gridwork that secures your wall and roof sheathing, acting like the rebar in concrete—they may be hidden, but they are crucial.
Why Girts and Purlins Are Critical to Barndominium Stability
- Load Distribution
One of the primary roles of girts and purlins is to distribute loads evenly across the frame of the structure. Metal buildings are subjected to various forces:
- Dead loads (the weight of the structure itself)
- Live loads (people, furniture, equipment)
- Environmental loads (wind, snow, seismic activity)
Girts distribute lateral forces (mainly from wind) across the vertical columns, while purlins distribute vertical forces (like snow or gravity loads) to the roof trusses and walls. Without them, concentrated loads could deform panels or buckle columns.
- Sheathing Support
Metal siding and roofing panels require backing to hold them in place securely. Girts provide a surface for attaching wall panels, while purlins do the same for roof panels. This ensures the outer shell of the barndominium remains flat and tight against the frame, which is vital for:
- Preventing leaks
- Enhancing insulation performance
- Resisting impact from windborne debris
Without girts and purlins, you’d have large unsupported spans of metal sheeting prone to oil-canning (visual warping) and failure.
- Preventing Racking and Structural Deformation
Racking is the term used when a structure shifts out of square under lateral pressure, like during high winds or seismic events. Girts play a vital role in resisting lateral movement by reinforcing the vertical columns, much like braces in timber framing.
Purlins help the roof frame resist warping or sagging, maintaining its shape under load. They also increase torsional rigidity, helping the roof stand up against high wind uplift forces common in tornado-prone areas.
- Energy Efficiency and Thermal Breaks
While not their primary function, girts and purlins can also support insulation systems such as spray foam, fiberglass batts, or rigid panels. Their spacing allows for insulation to fit snugly between the members, reducing thermal bridging and helping your barndominium remain energy efficient.
In systems like double-wall framing, the use of girts can also create a natural thermal break—a gap that reduces direct heat flow through the wall. This design trick can drastically reduce energy bills over time.
- Structural Redundancy
In structural engineering, redundancy is a good thing. It means that if one component fails, others can share the load and prevent catastrophic failure. Girts and purlins add multiple horizontal layers of structural redundancy to your barndominium.
This grid-like distribution of force provides a fail-safe mechanism, particularly important in:
- Extreme weather conditions
- Earthquake zones
- Large-span buildings with minimal interior framing
Types of Girts and Purlins
Barndominium builders typically choose between C-shaped and Z-shaped profiles, depending on application and load requirements.
C-Channel
- Shaped like the letter “C”
- Often used for edge conditions and where splicing is not needed
- Simpler to install but may require overlapping at joints
Z-Channel
- Shaped like the letter “Z”
- Better for overlapping spans between columns or rafters
- Offers stronger load transfer between sections
The spacing of girts and purlins varies depending on local building codes, snow/wind load ratings, and the dimensions of the building—but typical spacing is between 2 to 4 feet on center.
Common Mistakes to Avoid
Even though girts and purlins are fundamental to metal building construction, they are sometimes underestimated or incorrectly installed. Here are a few common mistakes:
- Improper spacing can lead to deflection and panel warping.
- Undersized members may not meet code or withstand intended loads.
- Failure to anchor properly can lead to twisting or buckling under wind pressure.
- Inadequate bracing between purlins and rafters can compromise roof stability.
Always work with a structural engineer or experienced metal building designer to ensure that the specifications meet both local building codes and the performance needs of your location.
Girts and Purlins in Pre-Engineered Kits
Most barndominiums today are built using pre-engineered metal building (PEMB) kits, which include pre-cut and pre-drilled girts and purlins as part of the package. These systems are designed with precision, reducing on-site labor and ensuring that every structural component—including the horizontal members—is accounted for and meets load requirements.
If you’re going custom or retrofitting an existing barn, make sure you don’t skip a structural analysis. Even minor oversights in girts and purlins can snowball into serious stability issues.
Final Thoughts: Never Underestimate the Horizontal Heroes
While girts and purlins may not be visible once your barndominium is complete, they are vital to the structure’s ability to withstand the forces of nature and the test of time. Think of them as the unsung heroes of your metal building—quietly doing the heavy lifting behind the scenes.
Incorporating the right girts and purlins, properly sized and spaced, is not just a matter of code compliance—it’s a matter of long-term safety, durability, and peace of mind. Whether you’re DIY-building or hiring a contractor, make sure these essential horizontal supports get the attention they deserve.
Are you planning to build a barndominium? Talk to a professional about your girts and purlins to make sure your dream home stands strong for decades to come.