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How do I know what size purlins I need?

Metal Roof

A purlin is one of the most important tools in architecture. This is a horizontal beam that provides structural support in buildings, typically the roof. Purlins themselves are usually supported by the walls of the building. While they are commonly used in metal buildings, they are sometimes used in structures that have a wooden frame. Purlins come in different types and sizes. Therefore, it is important for you to use the right purlin. 

The Types of Purlins

The two most common types of purlins are:

Wood Purlin: A wood purlin is typically used with cement sheeting. The wood works well with the rest of the structure to ensure the room enclosed by the roof is breathable. This allows someone to store organic material in the room such as grain or livestock. On the other hand, wood purlins can rot. To prevent this from happening, it is important to make sure the purlins are dried before installation.

Steel Purlin: The other option is the steel purlin. This is a lightweight beam that is stable, straight, and accurate. Steel purlins expand and contract to ensure they withstand temperature changes with ease. These purlins are usually manufactured with galvanized steel coated with zinc to provide rust protection. Finally, they are finished with paint that provides corrosion protection.

Selecting the Right Size of Purlin

Purlins come in varying sizes and can be installed in various ways. These factors are going to impact which purlin is chosen. The different installation methods are referred to as run systems. The run system is going to impact how far each purlin is going to stretch. Some of the most common run systems include:

  • Single Span System: One purlin spans the length of the structure
  • Double Purlin Span System: Two purlins are supported at the ends and in the center
  • Double Lapped System: The two purlins overlap slightly in the center to provide added support
  • Continuous Lapped: Purlins are supported at each end and by a series of equally spaced supporting purlins in the middle.

Once you know the run system, think about how many purlins you will need. When you are installing purlins, keep in mind that they are typically placed 16 inches apart. This is going to impact how many purlins you need. Once the purlin run system has been decided, it is time to select the purlin size. The sizes are as follows:

  • 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 information, it should be straightforward to take measurements and select the right size purlin. Then, they can be installed and provide support for the roof.

Trust ADCO Metals for Your Roofing Needs

At ADCO Metals, we are here to help you with your roofing needs. Our professionals take the time to listen to you and your needs. Then, we will work with you to come up with a solution. Contact us today to learn more about how we can help you!

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