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Everything You Must Know About Metal Building Purlin

Metal Building Purlins

You need to be aware of the best building materials to use when considering your structure’s durability and sturdiness. The roof offers comprehensive support and is one of the essential building components. In addition to protecting people from the elements, it also strengthens the building’s structural framework. This is why knowing everything about roofing, particularly metal building purlins, will help you choose the best type of prefab kit that suits your needs.

Steel purlins have become increasingly popular among homeowners and building owners for roofing needs, particularly when longevity and durability are involved. But if this is your first experience with purlins, it is essential to know their fundamentals to determine if these are the ideal options for you.

First, understand purlins for straight wall metal buildings and their purpose.

What Is Metal Building Purlin?

The roof deck or sheathing loads are carried by the purlins, supported by substantial rafters, building walls, steel beams, etc. Purlins are frequently used in pre-engineered metal construction systems, as well as both the conventional post-and-beam and more modern pole construction methodologies for frame construction, as opposed to closely spaced rafters.

Purlins come in many different forms and are divided into categories according to the materials they are made of and the way they are shaped. It can be used for many other things, such as supporting a floor or wall, because they provide a frame for the prefab kit and sheeting to rest on and are important to the structural stability.

Also Read: The definitive guide to prefab steel building kits and garages.

Purpose of Using Purlin Metal Building

To protect and add support, steel purlins help maintain the roofing materials and enable them to last for a very long time.

Purlin metal buildings have a layer of paint on the outside that offers excellent corrosion protection, and they are composed of sturdy galvanized steel. Another benefit of a steel purlin is that it is resistant to rot and pests, two major problems for wood. While a wood purlin may sag from moisture or crack from the dryness, steel purlins will not.

In comparison with other types of purlins, steel purlins are preferred because they have higher tensile strength, durability, toughness, and strength-to-weight ratios.

Metal purlins come in several varieties, each of which is characterized by their shape. The most typical kinds of metal purlins are covered below.

Types of Metal Purlins

  1. C- Shaped Purlin

As the name suggests, C purlins are arranged like the letters of the C alphabet and are typically used to support walls and floors. C-shaped purlins are constructed to form the walls and floor joists of a building shell structure, making them ideal for holding the beams needed for flooring. They also contribute C-segment purlins for door mounting, parapet rails, window trimming, and roof trimming.

Due to the comparable extensions on both purlins in Section C, single spans can be constructed using them. These are safe and freestanding, making it possible to manage them easily when installing them and providing stable support for the structure.


  • C-shaped purlins give a wide range of length choices.
  • There is no requirement for side cutting or drilling.
  • Steel purlins with a C shape are remarkably straight and lightweight.
  • In terms of durability and structure, they are trustworthy.
  1. Z-Shaped Purlin

Stronger than C purlin, Z purlin is typically used at joints and overlaps. Z purlins are horizontal beams that shape the roof and wall joints of shell structures. They serve as sheet support to hold the prefab kit firmly and securely in place as they are positioned between the steel buildings in Ontario.


  • It is relatively easier to install with pre-punched holes based on the design in detail and can be changed per the requirements.
  • Excellent performance, high strength, and impact resistance in the cross-section.
  • Due to their extreme adaptability and lightweight, Z-shaped purlins can be used in a wide range of different-sized structures.

Metal Purlin Finishes

There are two types of metal purlin finishes: Galvanized and Red Oxide. Now, which one is better?

  1. Galvanized Purlins

A zinc-alloy plating is applied as part of the process to create galvanized metal. This renders the substance corrosion-resistant, enabling it to withstand harm from even the harshest settings, such as chemical plants or sites close to seawater, where rusting is inevitable for unprocessed steel.

Galvanized steel is suitable for saltwater environments, although it is prone to oxidizing and can turn nasty white when exposed to moisture.

It is recommended to use Galvanized Purlins if:

    1. You desire a purlin that will survive the longest.
    2. No paint will be used on the purlins.
    3. The purlins are situated near the ocean.
  1. Red Oxide Purlins

Red oxide purlins that have a thin red oxide coating applied to them. The coating’s purpose is to stop rust during shipping. Galvanized purlins aren’t used in construction as frequently as red oxide ones. A primed red purlin’s key benefit is that it will cost you 25%–35% less than galvanized purlins.

The steel is ready for a top coat of paint due to the red primer. Without a final coat of paint, the red oxide finish provides minimal protection against the weather, and the purlins will rust quickly. Additionally, compared to a red oxide primer, galvanized steel is more challenging to paint.

It is recommended to use Red Oxide Purlins if:

      1. You are looking for some cheap purlins.
      2. The purlins are protected from the weather.
      3. You wish to paint the purlins a different color.

Selecting the Right Sizes of Purlin 

Purlins can be installed in a variety of ways and come in a variety of sizes. These elements will influence the purlin that is selected. The length to which each purlin can be stretched will depend on the run system, for which there are different installation strategies. The following are the most commonly run systems:

      • Single Span System: The structure’s length is covered by a single purlin.
      • Double Purlin Span System: Two purlins are maintained at the ends and in the middle.
      • Double-Lapped System: To add additional support, the two purlins slightly overlap one another in the center.
      • Continuous Lapped System: Purlins are supported at both ends and by a center row of supporting purlins that are equally spaced apart.

Once you are familiar with the run system, consider how many purlins you will require. Keep in mind that purlins are normally spaced 16 inches apart when constructing them. This will affect how many purlins you need. The size of the purlins should be chosen after the purlin run system has been selected. The following are the sizes:

      • A four-inch purlin can span 12 feet
      • A six-inch purlin can span 18 feet
      • An eight-inch purlin can span 25 feet
      • A ten-inch purlin can span 30 feet

With this knowledge, choosing the correct size purlin and taking measurements should be easy and simple. After that, they can be put in place to support the roof.

The Better Cost of Steel Purlin 

The cost is dependent on a number of variables, including the size and thickness of the metal used to construct the purlins, the land’s current market value, and the cost of labor, permits, and other materials.

Purlins with a heavier gauge will cost more than those with a lighter gauge. Steel is needed more for deeper purlins than for shallower ones. A 10″ deep purlin will also cost around twice as much as a 4″ deep purlin.

Spacing of Metal Purlin 

The metal sheets must be at least 50 mm wide to be quickly fixed to the purlins. When placed, roof purlins should be no more than 1.2 meters apart when using 0.7-mm sheeting and 1 meter apart when using 0.5-mm sheeting.

Gauges of Metal Purlin

The bulk of steel purlins is either 16 or 14-gauge thick. The purlin depths are 4, 6, 8, 10, and 12 inches.

Which Metal Purlin Is Required for Prefab Kit

An open-framed metal construction includes metal purlins. They will help hold up the metal prefab kit sheets. They are essential for preserving a roof’s structural integrity. An additional layer of roof protection will be offered by using the proper purlins with the correct spacing for your project. Here are some options available for metal purlins.

Types C Purlin OR Z Purlin
Gauge 12, 14, and 16
Size 4-12 inches
Finish Red Oxide and Galvanized


Trusting VOD Steel Building For Your Prefab Kits Needs

At VOD Steel Buildings, we provide panels, decking, and installation accessories for all your metal garages and steel building needs. Give us a call at 1-844-609-0505 to request a free quote for your project today!