Breaking Down a Metal Building: Detailed Anatomy of Every Frame, Truss, and Girt

Metal buildings are everywhere, from industrial warehouses to farm shops and even carports. But what exactly goes into one of these structures? What are the frames, the trusses, the girts, and how do they all fit together? Whether you are installing a simple metal carport or a larger building with storage, understanding how the components come together helps you ask the right questions and make better choices. It also helps to work more smoothly with your metal building dealer.

The anatomy of a metal building uses the same basic parts. And when you are asking top questions from buyers, things like “what is a girt?” or “how is the truss assembled?” will come up. Also, preparation is key, so site preparation before installation will matter just as much as the steel pieces themselves.

Let’s break it down step by step.

Site Preparation and Foundation

Why Does Site Preparation Matter?

Before any steel hits the ground, the site must be ready. You will want a level, stable surface, proper drainage, and the footprint marked out. Any mis-shape or uneven substrate means trouble later, frames will not align, columns lean, and panels don’t fit cleanly. So from the beginning, make sure your ground is cleared, debris is removed, soil is compacted, and any lay-down area for materials is arranged.

Concrete Footings and Anchors:

Once the site is ready, concrete footings or a slab are poured. The steel building’s main frame columns will anchor into these. The anchor bolts get set in the concrete at exact positions so that the vertical columns, beams, etc, align perfectly. Without correct foundation work, all of the subsequent frame construction suffers. When choosing a building like a custom metal carport, good site preparation dramatically reduces cost and headaches.

The Primary Building Frame (Columns, Rafters)

1. Columns – The Vertical Support

The vertical members of a metal building are the columns. These are anchored to the foundation and stand up to carry the building’s weight and loads from wind, snow, and other forces. They are primary structural members.

2. Rafters or Main Beams – Forming the Roof Support

Next are the horizontal or sloped beams/rafters that span between the columns and form the roof support system. Together with the columns, they make up the “main frame” or primary frame of the building.

3. Eave Struts and Frame Legs

At the point where the roof meets the sidewalls, the eave line, there are special members called eave struts. These struts help tie the roof frame and wall frame together. They are part of secondary framing, but still critical for the primary structural geometry.

Roof Trusses or Roof Frames

1. What is A Truss?

At its core, a truss is a carefully engineered triangular framework designed to distribute weight efficiently across wide spans. The triangle is nature’s strongest shape; it doesn’t bend easily, which makes it perfect for construction that demands both lightness and strength.

In metal buildings, trusses are typically made of high-tensile steel, giving them the ability to handle heavy loads such as roofing materials, wind pressure, or even snow accumulation. Some building designs use rigid frames instead of traditional trusses, but the goal remains the same: to create a solid, load-bearing system that bridges wide spaces without needing excessive support columns.

Trusses are especially important in wide-span metal garages or barns, where open floor plans are preferred. Without trusses, these structures would need multiple internal columns.

2. Anatomy of a Truss – How Each Part Works Together

Every truss may look simple at first glance, but it’s actually a complex system of interconnected members, each performing a specific role:

• Top Chords – These are the outermost beams forming the upper edges of the triangle. They handle the compression forces coming down from the roof load — including snow, rain, or roofing panels.
• Bottom Chord – This runs horizontally at the base of the truss and is responsible for tension. It ties the two ends together, preventing them from spreading apart.
• Web Members – These diagonal and vertical bars connect the top and bottom chords, forming multiple triangles within the frame. They distribute the load evenly throughout the truss, ensuring stability under pressure.
• Gusset Plates – These are the connection plates, usually made of thick steel, that join the chords and webs together at each joint. They ensure the truss behaves as one unit rather than a collection of individual parts.

Together, these components create a lightweight yet incredibly strong framework that resists bending, sagging, and warping. It’s a perfect example of how geometry and engineering come together in metal construction.

3. Truss vs. Rigid Frame – Which One’s Better?

While traditional trusses are made of interconnected beams forming visible triangles, many modern metal buildings now use rigid frames, large, solid steel beams shaped like a wide arch or portal frame.

• Trusses are typically used in structures where minimizing weight and cost is essential, such as barns, workshops, or long-span carports.
• Rigid frames, on the other hand, are more common in commercial buildings and large garages that need clear-span interiors.

Both systems are designed to carry heavy roof loads and withstand external forces like wind or seismic activity. So, the choice often depends on your building size, budget, and intended use.

4. Installing the Truss or Rigid Frame – Precision Meets Power

The installation of the roof truss or rigid frame is one of the most critical stages in metal building construction. It’s where the skeletal strength of the structure truly begins to take shape.

Using cranes, the steel trusses or frames are lifted into position and carefully aligned with the main columns. Every bolt, weld, and joint is checked to ensure the structure is perfectly square, plumb, and level. Once everything is anchored securely, the framework transforms into a single, unified system that can bear tremendous loads.

This stage marks a major milestone, the moment when your building finally begins to look like a real structure. The truss or frame now serves as the backbone for roof panels, purlins, and other structural elements that will follow.

For three-car and five-car metal garages, this step is especially important. These larger spans rely heavily on well-designed trusses and frames to maintain strength without adding unnecessary weight or internal supports.

Secondary Framing – Girting and Purlins

1. What are Girts and Purlins?

Once the primary frame is up, the next layer is secondary framing. These are members that span between the main frame to support the wall and roof panels.

• Girts are horizontal members attached to the sidewall or end-wall columns; they support the wall covering/panels.
• Purlins are horizontal members that support roof panels; they span from one rafter/truss to the next.

2. Role in Stability and Sheeting Attachment

These secondary members don’t just carry the panel loads; they also provide lateral support, brace the main frame, and form the substrate to which wall and roof sheets attach. For example, girts help the walls resist wind loads by transferring forces to the main frame.

3. Girt Quality and Placement Matters

Spacing, size, gauge, and installation of girts matter a lot. If it’s too light, too far apart, you will risk too much flexing or panel failure. This is why girts are essential in ensuring the stability of wall panels.

Wall & Roof Cladding – Panels, Trim, and Closure

1. Roof Panels and Wall Panels

With the frame, trusses, purlins, and girts in place, the next step is attaching the exterior skin: the metal wall panels and roof panels. These attach to the girts (walls) and purlins (roof). The panels also help create bracing and contribute to overall rigidity.

2. Trim, Flashing, and Openings

Openings like doors and windows get framed, headers installed, and trim added during installation. Flashing along edges ensures that weather elements do not damage anything stored inside. These finishing touches keep out water and seal the envelope. Moreover, offers aesthetics to the exterior.

3. Integration with Carports and Storage Options

If you are building a structure like a metal carport with storage, the same paneling and framing logic applies, whether you are adding a side storage room, a lean-to, or a full-enclosed area. Good design integrates the storage portion from the start so that girts, purlins, and frames align for both the open carport side and the enclosed side.

Why This Understanding Matters for Buyers

Understanding this technicality of a steel building installation is crucial. If you think it’s only for installers, you will be making a mistake while buying a new metal garage and any other structure for your needs. Let’s know why it matters.

Asking the Right Questions

When a supplier or builder mentions “girts,” “purlins,” “rigid frame,” “truss,” you will know what they mean. In fact, you will be better prepared when reading your quote, discussing with the installer, or checking your building’s plans.

Evaluating Quotes and Designs

If one quote says “16 gauge girts at 5′ spacing” and another says “14 gauge at 10′ spacing”, you will recognise the difference and know which may be more robust. You will know what matters: frame strength, connection quality, panel attachment, and foundation anchoring.

Customisation and Storage Integration

When you go for a custom metal carport, perhaps with extra width, tall doors, or a metal carport with storage attached, you will better understand why frames are heavier, why extra girts or purlins might be needed, and how the building is engineered accordingly.

Site Preparation is Half the Battle

Even the best steel frame needs a good foundation and site to shine. If you skip or shortcut the site work, misalignment, leaks, and panel issues will follow. This is why site preparation before installation is not optional; it’s essential.

Final Thought

Whether you are just exploring options for a carport or planning a full metal building, understanding the “anatomy” of how it’s built, from primary frame to girts to trusses, sets you up for success. Since these building parts can’t be effective alone, we have talked about other crucial parts and features above, so you do not get confused. Now ready to surprise your dealer with questions about trusses, frames, girts, and other parts of a metal building.