Cold Formed Anatomy
This page walks through the basic anatomy of a cold-formed steel building—showing how columns, rafters, purlins, girts, and bracing work together as a complete frame. Use it as a reference when reviewing plans, specs, or building quotes.
Terminology and layout here are general to cold-formed buildings. Final member sizes, spacings, and details are always based on project-specific engineering.
A cold-formed metal building shell is built from repetitive frames running down the length of the building. Each frame is made up of columns, rafters, and connections that transfer loads into the foundation. Secondary members—purlins, girts, and bracing—tie the frames together and support roof and wall panels.
The labeled diagram shows a typical clear-span frame with roof and wall members identified. When you read a plan set or specification, most component references will tie back to one of these basic elements.
- Primary frame: columns, rafters, and frame connections.
- Secondary framing: purlins, girts, struts, and bracing.
- Envelope: roof panels, wall panels, trim, and closures.
- Interface: anchor bolts, base plates, and slab/foundation.
Primary framing carries the bulk of the building loads—wind, snow (where applicable), live loads, and the weight of the roof and walls. In a cold-formed system, these members are typically fabricated from C- or Z-shaped sections, nested and bolted together to form built-up columns and rafters.
- Columns: Vertical members anchored to the foundation that support rafters and transfer loads into the slab or pier system.
- Rafters: Sloped members forming the roof line between columns. Often built from back-to-back C-sections.
- Frame Connections: Bolted joints where columns and rafters meet, designed to handle bending and axial forces.
- End Frames: Endwall frames that may be either full rigid frames or lighter endwall systems, depending on loads and openings.
Secondary framing supports the roof and wall panels and helps distribute loads back into the primary frames. Spacing, orientation, and member size are all engineered around code loads and panel requirements.
- Purlins: Members running along the roof that support roof panels and act as a diaphragm component.
- Girts: Horizontal members on the walls that support wall panels between columns.
- Eave Members: Transition between roof and wall framing, often tying purlins and girts together.
- Struts / Drag Members: Members that collect loads from roof and wall diaphragms and transfer them into braced bays.
Bracing controls building drift and prevents the frame from racking under wind and seismic loads. It also stabilizes slender cold-formed members during erection and under service loads.
- Rod or Strap Bracing: Diagonal bracing in the roof and walls to create braced bays.
- Flange Bracing: Small angles or channels that brace the compression flanges of purlins and rafters.
- Connections: Clip angles, bearing plates, and fasteners that tie secondary members to primary frames.
- Panel Diaphragm Action: Roof and wall panels themselves act as part of the lateral system when detailed for diaphragm behavior.
The cold-formed building shell sits on a foundation designed by others—typically a slab-on-grade with thickened edges, grade beams, or piers. Anchor bolts are set from the building reaction drawings, and base plates are detailed in the metal building plans.
- Foundation design is typically by the project engineer of record (EOR).
- Metal building reactions and anchor layouts are provided in the building submittal package.
- Edge conditions (recessed slab, stem wall, or flush mount) are coordinated early to avoid conflicts.
Use this anatomy guide alongside our Specification Checklist and Color Selection Guide, then send us your plans or start a design tool RFQ. We’ll translate the components you see here into a complete, engineered cold-formed building package.