What Is the Role of Purlins and Girts in a PEB Structure?
Updated: 2 days ago
Understanding Secondary Structural Members in PEB
A PEB structure works through a layered load transfer system. The primary frame, made up of columns and rafters, carries the major structural loads of the building. However, the primary frame alone cannot support roof sheets and wall cladding directly, since the spacing between rafters and columns is usually too wide for sheeting to span on its own.
This is exactly where secondary members like purlins and girts come in. They bridge the gap between the primary frame and the cladding, distributing the load evenly before passing it down to the main structure.
What Are Purlins and How Do They Function?
Purlins are horizontal structural members installed across the roof rafters. They provide support for roof sheeting and transfer the applied loads to the primary rafters.
Roof sheets are fixed directly to the purlins, which means purlins support the dead load of the roofing material along with applicable live and environmental loads such as wind pressure, rainwater and maintenance loads.
Key Functions of Purlins
Support roof sheeting and transfer loads to rafters
Provide lateral restraint and stability to the roof system
Help resist wind uplift forces acting on the roof
Maintain proper spacing for insulation and liner panels where required
Provide a suitable fixing base for roof cladding
Purlins are typically manufactured using cold formed steel sections, commonly in Z or C shapes, selected for their strength-to-weight ratio and ease of installation.
The spacing between purlins depends on structural load calculations, sheeting type, roof configuration and site-specific wind conditions. This is why a reliable pre engineered building company calculates purlin spacing in PEB structures based on actual project requirements rather than applying a standard spacing to every building.
What Are Girts and How Do They Function
Girts perform a similar role to purlins, but along the vertical wall sections of the building instead of the roof. They run horizontally between wall columns, providing the structural support needed for wall cladding sheets to be fixed securely.
Key Functions of Girts
Support wall cladding and transfer load to columns
Resist lateral wind pressure acting on building walls
Provide additional rigidity to the overall wall structure
Allow proper alignment for doors, windows and ventilation openings
Like purlins, girts are generally fabricated from cold formed steel sections, and their spacing is determined based on wall height, cladding type and wind load requirements specific to the project location.
Purlins vs Girts: Quick Comparison
Although their location differs, both components work on the same engineering principle of distributing load evenly across the building envelope before transferring it to the primary structural frame.
Why Correct Design of Purlins and Girts Matters
Many buyers assume that since purlins and girts are secondary members, their design does not need as much attention as the primary frame. This assumption can lead to serious structural issues over time.
Incorrectly spaced or underdesigned purlins can cause roof sheets to sag, develop leaks, or, in extreme wind conditions, get torn away due to insufficient uplift resistance. Similarly, poorly designed girts can lead to wall cladding instability, water seepage at joints and reduced overall building rigidity.
This is why any experienced peb structure design team always calculates secondary member spacing based on actual wind speed data, roof slope, cladding profile, and building height, rather than relying on generic industry assumptions.
Factors That Influence Purlin and Girt Design
Regional wind speed data as per IS 875 guidelines
Roof slope and overall building height
Type and weight of cladding material selected
Spacing between primary frame columns and rafters
Insulation or liner panel requirements, if applicable
Choosing the Right PEB Partner for Structural Detailing
Since purlins and girts directly affect the long-term performance of the building envelope, this is an area where engineering experience matters.
When evaluating PEB manufacturers near me, buyers should ask how secondary member design and spacing are calculated and whether the design accounts for local wind conditions and project-specific requirements rather than following a standard template.
A well-established PEB company in Nagpur with proper structural engineering and detailing capabilities should be able to explain how purlins, girts and other PEB structural components are designed and integrated into the overall building system.
Frequently Asked Questions
Conclusion
Purlins and girts may not be the most visible components of a PEB structure, but they play a critical role in supporting the roof and wall cladding system. These secondary structural members in pre engineered buildings help transfer loads to the primary structural frame while contributing to the stability and performance of the building envelope.
Proper design of purlins and girts, based on accurate structural calculations rather than assumptions, can make a significant difference to the long-term performance of a PEB structure. Working with an experienced team that understands PEB engineering, structural detailing and secondary member design helps ensure that these critical components are designed appropriately for the project.
Planning a PEB project and want structural detailing done right? Connect with PEB360 Solutions for guidance on purling, grit and complete structural design tailored to your project requirements.
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