When people dream about building a barndominium, they often focus on the open floor plans, the rustic aesthetic, or the cost-effective square footage. Very few spend time thinking about the horizontal members that brace the steel frame. Yet these components—purlins on the roof and girts on the walls—are what separate a building that stands for decades from one that develops costly structural issues within a few years.
Understanding the Framework
A barndominium relies on a rigid steel frame as its primary skeleton. That frame consists of vertical columns and horizontal rafters, but those members alone cannot resist the lateral forces that act on a building. Wind loads, seismic activity, and even the weight of roof-mounted equipment all push and pull against that frame.
Purlins are the horizontal beams that span across the rafters of the roof. They support the roof panels and transfer loads from the roof surface down into the primary framing. Girts serve the same function on the walls, attaching horizontally to the columns and providing a substrate for wall cladding while resisting wind pressure that tries to push the walls inward or suction that tries to pull them outward.
How Purlins Contribute to Structural Integrity
The roof of any building experiences significant vertical loads, but purlins do more than simply hold up metal panels. They brace the top flanges of the rafters, preventing those rafters from twisting or buckling under compression. Without proper purlin placement, the rafters would be susceptible to lateral-torsional buckling, especially during high wind events.
Purlins also create a diaphragm effect across the roof plane. When properly fastened, the roof panels work together with the purlins to distribute loads across the entire roof system rather than concentrating stress at individual connection points. This diaphragm action is critical for maintaining the rectangular shape of the building during asymmetric loading conditions.
The spacing between purlins matters enormously. Standard spacing of five feet on center works for most applications, but areas with heavy snow loads or high wind velocities often require tighter spacing. Engineers calculate these specifications based on the expected live loads, dead loads, and environmental factors for each specific location.
Wall Girts and Their Function
Wall girts face challenges that purlins do not. They must resist both positive pressure when wind pushes against the wall and negative pressure when wind creates suction on the leeward side of the building. This alternating load pattern demands that girts be securely attached to the columns with connections that can handle these reversing forces.
Girts also serve a secondary purpose that many barndominium owners overlook. They provide nailing surfaces and attachment points for insulation systems, electrical wiring, and interior wall finishes. The relationship between girt spacing and the dimensions of standard building materials affects installation efficiency and material waste.
By-Pass girts, which pass continuously on the outside of the columns, offer superior load transfer compared to flush-mounted systems. The by-pass configuration creates a more uniform load path and reduces the concentration of stress at column connections. This approach also simplifies the installation of insulation because the continuous girts create a consistent cavity depth.
The Connection to the Foundation
The stability provided by purlins and girts only matters if that stability transfers correctly to the foundation. Properly designed purlin and girt systems ensure that lateral loads reach the columns, travel down to the base plates, and enter the foundation without overstressing any single connection point.
Wind uplift on a roof creates tension forces that travel from the roof panels, through the purlins, into the rafters, and down the columns to the foundation anchors. Each connection in this load path must be designed for the specific forces it will experience. Many structural failures in barndominiums trace back to inadequate connections at critical points in this load path.
Material Choices Matter
Steel purlins and girts come in various gauges, with 14-gauge and 12-gauge being most common in residential barndominium construction. Heavier gauges provide more strength but also add cost and weight. The choice depends on local building codes, the size of the building, and the environmental loads expected.
Some builders attempt to use wooden purlins or girts in an effort to reduce costs or achieve a more traditional appearance. While possible, this approach introduces different structural characteristics. Wood expands and contracts with humidity changes, which can affect fastener tightness over time. Steel provides more consistent performance and better resistance to the moisture that often accumulates in metal buildings.
C-channel sections remain the most popular choice because they combine strength with ease of installation. The shape allows for simple clip attachments at columns and rafters while providing enough surface area for secure fastening of cladding materials.
Common Mistakes and How to Avoid Them
One frequent error involves insufficient attention to bridging between purlins. Bridging, or cross-bracing, between purlin lines prevents the purlins from rotating under load and distributes concentrated loads across multiple purlin members. Skipping bridging to save time or money invites long-term deflection issues.
Another mistake comes from ignoring thermal bridging. Unbroken steel girts conduct heat directly from the exterior to the interior, creating condensation risks and energy inefficiency. Thermal breaks, such as continuous insulation layers over the girts before attaching interior finishes, mitigate this problem.
Improper fastener selection also undermines the stability that purlins and girts provide. Fasteners must be matched to the specific materials being joined, with appropriate corrosion resistance for the local climate and sufficient length to engage the structural members.
The Foundation of Long-Term Value
The stability of a barndominium depends on countless elements working together. Purlin and girt systems may not be glamorous components, but their role in resisting loads and maintaining the building’s shape under stress determines how well the structure performs over decades of use.
Understanding these functions helps when evaluating contractor proposals and making decisions about materials and design. Buildings that compromise on these structural elements may save money initially but often face expensive repairs or reduced performance later.
The best barndominiums treat purlins and girts not as afterthoughts but as essential elements of a carefully engineered system. That commitment to structural integrity pays dividends in safety, comfort, and peace of mind for every owner who walks through the doors.