What is Purlin Span for Metal Roof ?

Posted on

Purlin is a well-known material in the field of architecture, structural building, or structural engineering. It is a horizontal bar that used to support building at the roof structurally.

There is an available purlin for every type of roofing material, including purlin span for metal roof which is the most common material type to use this item. Purlins are usually supported by rafter, building walls, or the weight of the roof deck itself. To know more about it, read the following passage below that explain it into details.

All about Purlin Span for Metal Roof

Purlin is a critical part of roof structure. Without it, there will be no frame for the roof sheet to lay on. There are several types of purlins that existed. They are typically categorized based on either material or the shape. Different types of it cater to different purpose, such as supporting walls or the roof floors.

See Also : Types of Pitched Roof

Purlin Span for Metal Roof

Here are the types based on the materials:

Wood Purlin

It is suitable to use for roof sheeting from fiber cement. They both can be combined well to make sure that the space below the roof or the building is breathable, thus making it a safe space to store whatever you need to inside like organic materials or livestock.

Steel Purlin

It is usually considered as the alternative of wood purlin. It has straight, accurate, dimensionally stable, and lightweight qualities. The steels can contract and expand reasonably under the pressure of temperature changes.

Meanwhile, there are two kinds of purlin span for metal roof based on the shapes, which are the C-purlins and Z-purlins. To identify whether yours is the earlier or the latter type, look for the end of the rails and check whether the shapes mimics the shape of letter “C” or letter “Z”. The roof purlin sizes of both shapes are ranging in length and thickness.

Z purlin span for metal roof

Generally, it will be manufactured due the requirement of the customers. The standard of purlin length will vary anywhere between 100 to 300 mm, while the thickness will vary anywhere between 1 to 3 mm.

If you want to know how to support roof purlins, they are usually supported by 2×4 or 2×6 struts or posts. For 2x4s purlins, the posts are spaced in 4 feet distance. For 2x6s purlins, the posts are spaced in 6 feet distance. If the space between posts is greater than 8 feet, then brace is needed to avoid buckling.

By the standard, the most used placement of purlin span for metal roof is five-foot intervals. However, it is important to note that expected load is a crucial factor while determining this. The heavier the load, the purlins have to be installed in shorter distance between one another.

Here are several useful tips for purlin installations:

  1. Have them installed by following the edges or sides of your roof. Placing the roof along the perimeter of your roof is important. They also have to be installed around the building’s penetrations like electric pipes, plumbing pipes, skylights, and others.
  2. Double them up in valleys. Due to the angle that created in the valley, it is necessary to double the purlins. Put the purlins on each side of the angle.
  3. Follow the correct screw pattern. You may refer to the installation manual for this step. Place the screw by 2 inches and double it at on-center locations.

Even though the installation of purlin span for metal roof is recommended, it is not required. Some regions do not require the use of purlin system based on their building code for new constructions. Nowadays, it is more common to see it used for re-roofing project.