Z vs C Sections (and Why You Need Both in Your Steel Building)
12 December 2022
Shane Barker, Business Development Manager
C and Z sections are both important parts of your structure, allowing us to fix material to the roof and walls in order to create the finished structure.
In this article, Shane and Julian explain the differences between Z vs C purlins, what they’re used for, and why structural steel buildings far outweigh purlin-only structures when it comes to strength and longevity.
CONTENTS
How Are C and Z Sections Used in a Steel Building?
IN BRIEF
- C and Z sections are generally used as roof purlins or wall girts, helping to create the main ‘skeleton’ of your building that other materials are fixed to.
- C purlins are more lightweight and are normally used to support walls and floors.
- Z purlins are stronger and used for roofing and walls.
- All our structural steel buildings use heavy RHS I and H beams, along with web trusses formed out of RHS & SHS. However, C and Z sections are also used as a lighter alternative for specific areas where load-bearing is less of an issue, and a reduction in overall weight benefits the final structure.
- Reducing the weight of the building means less steel, and less material cost – you can save money through efficient structural engineering.
Both C and Z sections are commonly used in steel structures. Manufactured from GALVASPAN® steel, these hot-dipped zinc-coated structural steel sections are roll-formed into purlins for commercial and industrial buildings.
Made with a high-tensile steel substrate, GALVASPAN® steel C and Z sections are strong, durable and highly corrosion resistant. Their purpose is to support the roof and wall materials, allowing connections between the main portal frame and the cladding materials.
C and Z sections are generally used as roof purlins or wall girts, helping to create the main ‘skeleton’ of your building. When used in the roof, Z purlins provide support and transfer forces down through the columns and into the footings, creating a structurally sound building. C sections are used along the eaves to help support the guttering.
Both C and Z sections are fixed to the portal frame, supporting the weight of wall materials and roof components such as Colorbond sheeting and any solar panels or HVAC systems. Roof purlins also help support environmental loads such as the weight of snowfall.
What are C Sections Used For?
As the name suggests C purlins are shaped like the letter C and are generally used to support walls and floors. They are used to shape the shell of the building, creating a skeleton on which to construct the walls of the structure.
Made from roll-formed steel, these purlins are usually 1mm to 3mm millimetres thick, making them lightweight but not as strong as structural steel.
C sections are always used at the eave to support the guttering, and in smaller sheds with bays under 6m wide, C sections can be used as support beams.
"Once your bays get over 8 metres wide, C sections become overly large and impractical, and Z sections are used instead."
- Shane Barker, Steelcorp
What Are Z Sections Used For?
Z purlins are somewhat stronger than C purlins due to their interlocking shape. They are typically used at joints and overlaps, giving structure to the roof and wall joists. Z purlins function as roof and wall purlins and girts, sitting between the COLORBOND sheets and the building. They act as a support to securely fix the cladding in place.
Because they can be overlapped, steel Z sections can overlap portal frames to brace the bays and allow for smaller Z sections. They can also be used in a more flexible manner, as unlike C sections, they can be fixed at different angles. C sections can only butt up against the frame, whereas Z sections can be oriented in different ways to achieve different structural outcomes.
Good to Know: Purlin Only vs Structural Steel
Purlin-only structures are only suitable for spans under 10m and aren’t used for heavy-duty applications like storing machinery or industrial manufacturing. A minor bump or two and your building could suffer damage that’s difficult to fix. Lots of bracing is required to get a requisite level of strength, but it still doesn’t compare to the rigidity of structural steel.
It’s good to know that at Steelcorp, all our structures are considered structural steel buildings, designed using heavy hot-formed RHS I and H beams to give the required strength in critical areas, along with web trusses formed out of RHS & SHS.
However, C and Z sections are also used in our steel building designs: these offer a lighter alternative for specific areas where load-bearing is less of an issue, and a reduction in overall weight benefits the final structure.
Using a combination of C and Z sections and steel members helps us deliver cost efficiencies for our clients, whilst also ensuring the building is engineered to a high standard.
Julian Luvara from Eren Engineering explains why.
“Structural engineers are always aiming for the most efficient design – not just for cost efficiency, but also as an environmentally sound choice, because structures shouldn’t be overengineered unnecessarily. This means designing a building with the strongest, most resource-heavy materials for every single component is not always a good idea."
- Julian Luvara, Eren Engineering
Tap Into Our Structural Engineering Expertise at Steelcorp
Understanding the interplay between different elements of your building is what structural engineers specialise in, and involving yours from the early design stages will ensure that the right options are selected to give you a high-quality building.
Contact our team for help designing an efficient, cost-effective structure.
