Girts and purlins are structural elements used in buildings, particularly those with metal frames, serving specific purposes in supporting the roof and walls.
In essence, roof purlins are used to support metal roofing panels, while wall girts are used for the fastening of metal siding. They act as secondary framing members connecting the primary structural frame (like columns and rafters) to the exterior cladding.
Understanding Purlins
Purlins are horizontal beams that run perpendicular to the main structural members (rafters or trusses) on the roof. Their primary function is to provide support for the roof deck or cladding.
- Function: To transfer the load from the roof covering (like metal panels, insulation, snow, and wind) to the main roof rafters or trusses.
- Location: On the roof, spanning between rafters or trusses.
- Material: Typically made of steel (such as C-channel, Z-section, or hollow structural sections), but can also be wood or concrete in other construction types.
- Application: Roof purlins are used to support metal roofing panels. They provide a continuous surface for fastening the roofing material securely.
Think of purlins as the cross-members that hold up the roof panels, ensuring they don't sag between the main support beams.
Understanding Girts
Girts are horizontal beams installed on the walls of a building, spanning between the main vertical structural members (columns or studs). Their main role is to support the wall cladding.
- Function: To transfer the load from the wall cladding (like metal siding, insulation, and wind pressure) to the main vertical columns or studs.
- Location: On the walls, spanning between columns.
- Material: Similar to purlins, often made of steel (C-channel or Z-section), but can also be wood.
- Application: Wall girts are used for the fastening of metal siding. They create a framework to which the siding panels can be attached firmly and evenly.
Consider girts as the horizontal members on the walls that provide attachment points for the siding, keeping it stable and aligned.
Key Differences Summarized
While both girts and purlins are secondary horizontal framing members, their location and supported element differ:
| Feature | Purlins | Girts |
|---|---|---|
| Location | Roof | Walls |
| Supported | Roof cladding (e.g., metal panels) | Wall cladding (e.g., metal siding) |
| Spans Between | Rafters or Trusses | Columns or Studs |
| Primary Role | Support roof loads | Support wall loads & provide attachment |
In metal building systems, girts and purlins are crucial for creating a framework that is strong, stable, and ready to receive the exterior finish materials.
