Portal frame sheds

What is a portal frame?

What is a portal frame?
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Investing in a new shed is a big decision. So what is a portal frame and is it the best option for you?

In this article, we outline what a portal frame is and cover everything you need to know about the structural design, key components, and advantages of portal frames. 

We also explore why structural steel is the best option when building your portal frame shed, helping you make an informed decision. 

Structural design of portal frame sheds

A portal frame consists of two upright columns connected at the top by multiple rafters. These rafters are bolted together at the haunch joints and apex joints, providing a framework on which the purlins, girts, and cladding can be mounted. The key components of a portal frame are as follows:

  • Pier Footing — Piers are bored vertically into the ground below the columns and include a cast-in bolt cage that the columns are attached to.

  • Columns — Columns run vertically from the foundation to the rafters, supporting the roof and walls. 

  • Rafters — Rafters run from the apex to the top of the columns, creating the roof frame.

  • Apex joint — The apex is the highest point of the building where the rafters are joined together with a plate or bracket. 

  • Haunch joint — The haunch joint is the connection between the top of the columns and the rafters. 

  • Purlins — A purlin runs horizontally between rafters, providing support for the roof cladding.

  • Girts — Girts run horizontally on the outside of the columns, providing a framework for the wall cladding. 

Portal Frame structural design

Advantages of portal frames

Large clearspans

One of the main benefits of a portal frame is that you can gain a large open space inside your shed. With the right engineering and materials, a portal frame can be fully self-supporting from inside to outside. This means there is no need for additional supports inside the frame, maximising the usable internal space for storage and machinery. 

Cost-effective

Portal frames are one of the most cost-effective construction methods as they put the structural members to their best use, spanning the width of the building and maximising the open, usable space below. Most often our engineers find that propping the frame in the centre is not advisable until after a 36m span! In addition, our clients have found that minimising obstacles inside a building leads to more effective use of the space.

Efficient prefabricated construction

With a portal frame, the structural steel elements can be prefabricated into sections before being delivered to the building site. As the components are welded and bolted together in advance, on-site assembly is quick and easy. For an even faster construction time, check out our Durakit sheds — pre-designed, in stock and available in under 4 weeks. 

Strength and durability

Portal frames are strong and durable, particularly when made with structural steel. This means they are well suited to large-scale sheds for a range of purposes, including agricultural, industrial, commercial, and more. At ABC Sheds, we also manufacture cyclone-rated sheds with fully fabricated steel frames that can withstand the worst storms. 

Portal frames — Structural steel vs roll formed steel

The two main options for portal frame construction are roll-formed steel and structural steel. Both can be used in portal frame buildings but each suits a different set of requirements. Generally, roll-formed steel is best used in smaller buildings and garages while structural steel is best for large sheds and buildings.  

What is roll-formed steel?

Roll-formed steel is made with high-tensile sheet metal that is rolled into a “C” shape. It is also called cold-rolled steel or c-section steel, typically measuring as little as 1-2mm thick. It is most suitable for smaller spans up to around 12m for domestic sheds and garages and light commercial applications.

Due to the light weight of the material itself, cold-rolled sections are heavily dependent on their engineered shape, meaning that any dent, rust, or damage could be cause for concern for the structural integrity of the building. Additionally, roll-formed steel cannot support additional weight from features like a gantry crane, solar panels or other mounted services. For most large-scale purposes and wider shed spans, we recommend structural steel instead. 

What is structural steel?

Structural steel frames are far stronger than roll-formed steel, making them more suitable for any shed larger than 250 square metres. 

Measuring between 5mm to 20mm thick, structural steel can support more weight – such as a gantry crane – and span over 60 metres with no centre supports. This is far more practical for larger sheds and varying storage needs. Structural steel is also far more weather-resistant, making it more suitable for harsh Australian conditions. In an agricultural or industrial environment, a shed can expect far more ‘bumps and nudges’ with all the heavy machinery moving every day. A structural frame will prove far more robust than a cold-rolled frame shed. 

A structural steel shed frame is cut and welded to your requirements, giving you endless options for the design, shape, and size. The structural elements will also arrive at your site as prefabricated sections, making the assembly process much quicker.

Structural Steel Sheds Australia

Here at ABC Sheds, we specialise in large structural steel buildings, starting at a minimum size of 18 metres long, 12 metres wide, and 2.4 metres high. However, most of our customers opt for much bigger sheds to maximise functionality and adaptability. The advantages of working with our team include:

  • Portal frames with clear spans up to 60 metres.
  • 25-year guarantee.
  • Engineered to Australian building standards.
  • Hot dip galvanised steel protective coating. 
  • Fabricated structural steel construction. 
  • COLORBOND® and Zincalume® cladding. 
  • Customisable designs with a range of optional features. 


If you’re looking for a reliable shed, contact us to request a quote today. Alternatively, download our full sheds brochure to learn more about our range and explore the possibilities.