Primary Framing
Endwall Rafters for Metal Building Gable Ends
Definition: An endwall rafter is the sloping member along the top of a building endwall that supports the end bay purlins and the top of the endwall columns. In post-and-beam endwalls it spans between endwall columns; in expandable endwalls it is part of a full rigid frame.
Key facts
- Endwall rafters carry about half the tributary roof load of an interior frame.
- In post-and-beam endwalls they are often cold-formed C-sections or hot-rolled channels.
- Expandable endwalls use a full rigid frame rafter instead.
- Purlins usually bear on the rafter or connect with clips to its web.
- Rake trims and flashings close the roof edge above the endwall rafter.
Role in the structure
The endwall rafter carries roof load from half a bay of purlins, which is roughly half of what an interior rafter carries. It delivers this load to the endwall columns below. It also acts as a horizontal support line for endwall wind, passing column top reactions into the roof bracing system.
How is an endwall rafter different from an interior rafter?
An interior rafter spans the full building width or between interior columns, and carries a full bay of roof load. An endwall rafter in a post-and-beam endwall is supported at many points by endwall columns, so its spans are short and its section much lighter.
This makes post-and-beam endwalls economical, but the endwall rafter cannot work as a portal on its own. If the endwall columns are removed, the rafter needs to be replaced or reinforced.
How do purlins connect at the endwall?
Purlins in the end bay may sit on top of the endwall rafter or be flush-framed into its web with clips. Sitting on top allows a small roof overhang at the gable; flush framing gives a cleaner rake detail.
The arrangement affects the rake trim, gable overhang and roof extension details, so it should be coordinated with the architect.
How do endwall rafters support roof extensions at the gable?
Gable roof extensions are cantilevered beyond the endwall line using extended purlins or outrigger members. The endwall rafter supports these and transfers their loads to the endwall columns.
Wind uplift on overhangs is significant, so the extension and its connection to the endwall rafter must be checked for uplift as well as gravity.
Materials & coatings
- Cold-formed C-sections or back-to-back C-sections in structural steel.
- Hot-rolled channels or beams for longer spans.
- Built-up rafters for expandable rigid endwalls.
- Primer or galvanized finish matching the endwall columns.
Design considerations
- Tributary roof load from the end bay.
- Spacing of endwall columns and resulting rafter spans.
- Purlin connection type and gable overhang.
- Roof extension or gable canopy loads.
- Future expansion requirements.
Fabrication
- Cut or roll-form sections to length and slope.
- Add column connection clips and purlin clips.
- Splice long rafters with bolted plates where needed.
Erection
- Erect endwall columns and rafters as a unit or column-first.
- Check rafter slope and alignment with interior frames.
- Fix purlins and roof bracing in the end bay before cladding.
Inspection & quality
- Confirm alignment of the rafter line with adjacent frames.
- Check column-to-rafter connections.
- Verify rake trim support before roofing.
What to include in your RFQ
- Endwall type: post-and-beam or expandable rigid frame.
- Gable overhang or roof extension width.
- Rake trim and gutter style.
- Future expansion plans.
3D model & IFC of this component
Rotate the model, isolate the component and download its IFC4 file for your BIM coordination model.
IFC entity: IfcMember. Illustrative geometry for coordination and learning. Final member sizes come from the project design.
Frequently Asked Questions
Are endwall rafters always lighter than main rafters?
In post-and-beam endwalls, yes. In expandable endwalls, the end frame is often designed for nearly the same load as an interior frame to allow future bays.
Can I add a canopy at the gable end?
Yes, the endwall framing can support a canopy if the load is included in the design. Tell the engineer the size and position.
What is a rake?
The rake is the sloping edge of the roof at the gable end, directly above the endwall rafter, closed with a rake trim.
Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.
