Parts of a Metal Building – Labeled Steel Frame Diagram

All 20 parts on the diagram

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Steel framing 13

Rigid frame Columns and rafters joined stiffly. That lets it stand without bracing in its own plane.
Purlins They span from frame to frame and carry the roof panels.
Girts They are fixed to the columns and carry the wall panels.
Bracing Rods or cables that pass wind loads down to the foundation.
Eave strut It carries the edge of both the roof and wall panels.
End wall column It supports the girts of the end wall.
Column It carries the load from the rafter down to the foundation.
Rafter The main beam that supports the roof. The purlins sit on it.
Haunch The frame is deepest here, where the bending is greatest.
Base plate It rests on the foundation. The anchor bolts hold it down.
Anchor bolts Also called anchor rods. They hold the frame down to the foundation.
Flange brace It steadies the inner flange of the rafter sideways.
Base angle The bottom of the wall panels is fastened to it.

Panels and trim 7

Roof panels They are fastened to the purlins.
Wall panels They are fastened to the girts.
Gutter It carries rain from the roof to the downspouts.
Downspout It takes the water down to the ground.
Ridge cap Also called ridge roll or ridge flashing.
Framed opening Two jambs at the sides and a header across the top.
Rake trim It closes the gap between the roof panels and end wall panels.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it: the Metal Building Manufacturers Association's glossary (Internet Archive copy, https://web.archive.org/web/20180515165501/http://mbma.com:80/Learn_Glossary.html); the US Department of Defense guide specification UFGS 13 34 19, Metal Building Systems (https://www.wbdg.org/FFC/DOD/UFGS/UFGS%2013%2034%2019.pdf); a metal building maker's erection manual (Internet Archive copy); SteelConstruction.info, Portal frames (https://www.steelconstruction.info/Portal_frames); and Wikipedia, text only: Purlin, Girt, Portal frame and Carport. No maker is named on the page. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; a schematic of no maker's building, nothing traced. Licence: own work

How it works

The parts of a metal building fall into three sets: the rigid frames, the purlins and girts that run between them, and the panels and trim on the outside. The first drawing shows all three; the second cuts through half of one frame.

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Frames, then purlins and girts, then panels

The rigid frames stand across the building, one at each bay line. Purlins run over their rafters and girts along their columns, with an eave strut where roof meets wall. The roof and wall panels are fastened to those. Crossed bracing in one bay passes wind loads down to the foundation.

One frame, foot to ridge

Each frame is a column and a rafter on each side. The corner where they meet is the haunch, the deepest part. At its foot the column stands on a base plate, held to the foundation by anchor bolts. Flange braces run from purlins to the inner edge of the rafter.

The parts of a steel building have other names too: a rigid frame is also a portal frame, and girts are side rails.
The ridge cap is also called ridge roll or ridge flashing.

Questions and answers

What are the main parts of a metal building?

Primary framing, secondary framing and cladding. The primary framing is the rigid frames. The secondary framing is the purlins, girts and eave struts that span between them. The cladding is the roof and wall panels, finished with trim, gutters and downspouts.

What is the difference between a purlin and a girt?

Both are horizontal members that carry the panels. A purlin is in the roof and supports the roof panels. A girt is in a wall, fixed to the columns, and supports the wall panels.

What are the parts of a carport?

A metal carport is the same idea with no walls: a frame of leg posts and rafters, roof panels on top, braces at the corners and anchors that hold it to the ground. Some have gutters.

What is a rigid frame in a metal building?

A frame of columns and rafters joined so stiffly that it stands in its own plane without bracing. The columns and rafters are often tapered, and deepest at the haunch where they meet.