If the building is topped with a roof, it is partly because of the support of the purlins. Each of the straight metal rods that support the roof panels is called a purlin. The metal purlin is very common in steel buildings. It is supported by the rafters and walls, which is important to keep the building structure together. So, what is the usual spacing of metal roof purlins?
Since metal purlins come in a variety of shapes and sizes, let’s move on to them. Learn what they do, why they are useful, and how they can be integrated into your project.
Table of Contents
What is a Purlin?
So, what is a metal purlin? In a metal roof or steel building, purlins are horizontal structural members supporting roof panels. They are usually made of steel or aluminium and are usually installed perpendicular to the rafters or trusses.
The metal purlin is an additional component of the framing that supports the decorative roof panels. It spreads the weight evenly across the rafters or trusses, thus preventing the roof from sagging or buckling.
History of Purlins
Although modern metal purlins are a product of the industrial revolution. However, purlin-like structures have been around since ancient times. In the past, people would use thatch or clay to build roofs, thus spreading the weight of the roof. As technology advanced, metal purlins became a better choice than wood supports. This is because they are stronger, last longer, and are easier to install.
Today there is a wide range of purlins available such as sleeve, butt, double span and heavy end. These metal purlins are widely used and installed in different buildings. For example, commercial buildings, warehouse buildings, logistics, energy, and automotive industry buildings.
What Are the Uses of Purlins?
In metal roofs and steel-frame buildings, purlins are an important part of the structure. Their specific uses include the following:
Load Distribution
Metal purlins are important for distributing the weight of the roof covering (e.g. metal roof panels) to the major building components (e.g. beams or trusses). This is because purlins can spread the weight around, thus avoiding an unstable centre of gravity. This allows the weight of the roof to be properly supported.
Supporting Structure
Metal purlins provide structural support to the roof system, making the building more stable as a whole. Typically, purlins are arranged horizontally along the length of the roof of a steel building to connect and support vertical framing members such as columns or studs.
Spanning Capacity
Metal purlins can help the roof cover more area by doubling the longest single-span dimension of the rafters. To avoid unnecessary lateral forces, make sure that the beams are properly supported and close to the vertical.
Stability and Stiffness
Metal purlins provide stability and stiffness to the entire side of the building. They stop lateral forces such as wind or earthquake from acting too strongly on the roof. Thus, the roof system does not sway or change shape too much. This very important lateral stability keeps the house strong even in bad weather.
Fixing Points for Roofing Materials
In different metal roofing systems, metal roofing sheets or panels are attached to purlins. The metal purlins provide a stable, level area for installing the roofing material. It ensures that the covering is well-supported and spread evenly over the building.
Moving the Load to the Main Frame
Metal purlins transfer the weight of the roof covering to the main frame of the building. The mainframe usually consists of columns and beams. This load transfer is important to keep the whole system structure strong and prevent individual components from being too heavy.
Adding Insulation and Other Amenities
In addition, metal purlins can be utilized as platforms for installing insulation and services such as electrical wiring or HVAC ducts. This is particularly useful in commercial and industrial buildings. This is because in these buildings the roof area is used for a variety of purposes.
Adjustment of Roof Slope
Metal purlins help in changing the pitch or slope of the roof. It allows rainwater to drain properly without accumulating on the roof surface. Correct metal roof pitches are important to prevent ponding, leaks and long-term damage to the roof structure.
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Purlins for Metal vs. Wood Buildings
More and more people are choosing metal buildings over wood buildings. One reason is that metal buildings are stronger, last longer, and require less maintenance than wood buildings. Metal buildings use less energy than wood homes and can be recycled after use.
In addition, the roof of a metal building is different from the roof of a wooden building. Purlins for metal roofs and steel frame buildings are usually made of steel or aluminum. It is very important to choose the right material so that the structure is strong enough to withstand the load.
What is the Purlins Spacing for Metal Roofs?
The width of the metal sheets should be at least 50 mm to facilitate the connection with the purlins. For installation, if the thickness of the metal sheet is 0.7 mm, the spacing between purlins should not exceed 1.2 meters. If the thickness of the metal plate is 0.5 mm, the spacing between purlins should not exceed 1 meter.
Therefore, the distance between metal purlins should be based on the weight that the structure can bear and the weight that the metal plate can bear. The heavier the load, the shorter the spacing between metal purlins. To determine the purlin spacing for different metal roofs, a metal panel and purlin load chart is required.
How many metal purlins are needed for a building project depends on the spacing, which will affect the cost of materials. If more purlins are needed, the material cost will increase. While needs vary from one metal building to another, this is a good general rule to follow. Before completing or installing any purlins. If you are unsure about anything, consult an experienced expert.
What Are the Advantages of Metal Purlins?
Metal purlins can be made of steel or aluminium and are ideal for supporting the top of steel buildings. Because metal purlins are lightweight but strong, they can span more. This means that there is less need for support in the center and it is easier to design a clear-span building.
Insects, fire, and rot will not damage metal purlins. Therefore steel buildings can remain strong for a long time. In addition, metal purlins are easy and inexpensive to install. Therefore the overall building is more efficient. Metal purlin can bear more weight and is weather-resistant. Therefore it is a good choice to ensure the stability and long-term use of the roofing system.
Summary
Metal purlins usually provide structural support for roofs and walls. They are important for distributing the weight of the roof covering to the main framing structure. This way the building does not become too heavy and remains stable.
In addition, metal purlins are usually made from materials such as steel, aluminum, and galvanized steel. The choice of material depends on the needs of the structure, the surrounding environment, and the project budget. Factors that determine the size and spacing of metal purlins include the type of roofing material, the length of the roof, and local building regulations. These parameters are usually determined by engineers and architects based on the unique needs of each building project.
