Steel framing
Purlins vs. Girts: Roof and Wall Secondary Framing Explained
Understand the different locations and duties of purlins and girts, then coordinate member marks, cladding interfaces, openings, and replacement requests.
Locate the member in the building
In a metal building, purlins support roof panels and girts support wall panels. These secondary members connect the cladding system to the primary framing. MBMA's educational material uses this roof-versus-wall distinction to explain how the building components fit together.
Names are most useful when tied to a location. A photograph of a loose C or Z section cannot reliably identify whether that piece belongs in a roof, wall, opening, or another framed condition. Record the member mark and the elevation or roof area first.
References: Metal building systems: components and secondary framing
Compare roof and wall coordination needs
The distinction changes the questions asked during a takeoff or replacement review. Use the table to build separate roof and wall material lists even when some profiles look alike.
| Topic | Purlin | Girt |
|---|---|---|
| Primary location | Roof framing | Wall framing |
| Cladding interface | Roof panel and roof attachment details | Wall panel and wall attachment details |
| Special conditions | Ridge, eave, roof openings, and transitions | Corners, doors, windows, and wall transitions |
| Useful drawing | Roof framing plan and sections | Wall elevations and framing details |
| Replacement record | Roof bay and piece mark | Wall line, elevation, and piece mark |
Treat secondary framing as part of the system
MBMA describes primary frames, secondary members, and cladding as interdependent components. The term secondary is a description of their place in the system, not a suggestion that changes are minor.
A new door opening is a good example. Removing a girt where the opening will go leaves questions about the surrounding members, jambs, cladding support, and connections. The useful next step is an opening-framing detail coordinated with the existing building, not a field decision to cut and reconnect the interrupted member.
References: Metal building systems and design resources
Capture orientation and support details
A component list should state which way each member faces and how it meets the supporting frame. Include lap or splice information where shown, together with holes and accessory connections. Identify conditions that differ at end bays, corners, and transitions.
When surveying existing work, take a wider image showing the member's position and a close image of each end connection. Add a sketch with the mark and viewing direction. This prevents a dimension or hole pattern from being interpreted backward when the replacement is discussed off site.
Build a practical replacement request
A replacement request needs more than a nominal depth. Organize what is known, what is measured, and what requires confirmation. If an existing marking is unreadable, say so; a guessed grade or thickness can create a false impression of certainty.
- Identify the building area, bay, elevation, and member mark.
- Provide the original drawing or manufacturer information where available.
- Record profile geometry, length, coating, and readable markings.
- Include support and splice details with orientation.
- Describe attached cladding and any planned changes to it.
- Keep the responsible designer's replacement decision with the purchase record.
Keep accessories with the right package
Separate roof accessories from wall accessories in the material schedule. Assign bridging, clips, closures, and opening pieces to the areas that need them rather than hiding them in a miscellaneous allowance. This helps the crew identify whether an incomplete delivery affects a specific area or the whole job.
If two suppliers divide the packages, record the interface responsibility. A clear list of who supplies each connection component is more useful than an assumption that it comes with the adjacent member.
Common questions
Are all purlins and girts cold-formed C or Z sections?
No. Those are common configurations, but the building design may use other members. Identify the actual specified section and its role rather than relying on a typical profile.
Can a spare roof purlin replace a damaged wall girt?
Not without a reviewed comparison of the member and its connections. Similar appearance or nominal depth does not establish compatibility with the wall system.
Sources & further reading
Use the current documentation for the exact product and project. Source links do not imply a partnership or endorsement.
- Metal building systems: components and secondary framing Metal Building Manufacturers Association
- Metal building systems and design resources Metal Building Manufacturers Association
Prepared with AI assistance. Linked references require current project-specific review. How these guides are prepared.
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Explore the catalog references and compare the published options with your project documents. Products sharing a guide are not necessarily interchangeable.
Prepare a supply inquiry
- Record the project drawing or detail and the specified product, profile, or system.
- List the complete configuration, physical units, quantities, and cuts per piece.
- Request current manufacturer documents; confirm compatibility, price, and availability before ordering.
- Obtain the responsible professional's review for loads, code requirements, or installation.