1. What is the definition of roof purlins?

Crossbar is a familiar and popular term, but for those who are not in the construction industry but just name it, it is difficult to understand what a crowbar is. In fact, purlins are a horizontal structural component of the roof with the role of bearing the load of all roof floors, covering materials such as corrugated iron, tiles... and are supported by original columns, building walls or steel frame.

Flat-roofed houses in urban areas rarely use beams, however, if it is a corrugated iron house or a tile roof, it is required to have beams, because without it we will not be able to put any material on the roof.

2. What types of roofing purlins are there?

Purlins can be classified in two ways: their composition and shape.

2.1 Wooden purlins

When the construction industry was not yet developed, wooden purlins could be considered the number one choice and were used very commonly. However, due to some disadvantages such as being susceptible to termites, not having high durability, easily catching fire... wooden purlins are gradually being replaced by steel purlins.

Currently, wooden purlins are only used a lot in level 4 houses in rural areas or houses that want to be built in an ancient architectural style. Steel purlins have wider and more flexible applications, so the following points of this article will discuss steel purlins.

2.2 Steel purlins

Steel purlins are widely used in steel frame roofs, prefabricated steel buildings or used as frames for factories, steel beams, and civil works with steel trusses for warehouses. Steel purlins are quite diverse in shape, produced in different lengths, sizes and positions of punching holes according to customer requirements; Made from cold-rolled, hot-rolled or hot-dip galvanized raw materials.

Steel purlins can directly replace wooden purlins with many outstanding advantages.

2.2.1 Advantages of steel purlins

While learning the answer to the question "What is purlin?", many people are probably also interested in its advantages. So what characteristics do steel purlins have that make them so widely used?

• Steel purlins have high durability, good hardness, and do not have to worry about rotting or termites like wooden purlins.
• Stable in quality; no twisting during construction; No bending or sagging after many years of use.
• Light weight, neat structure suitable for high-rise building designs.
• No worries about fire, less affected by weather or environmental factors.
• Steel purlins come in many shapes and sizes, so they are highly flexible and can be processed according to customer requirements.
• Helps enhance the aesthetics of modern style designs.
• Relatively cheap and economical cost. Previously, to use wooden purlins for a long time, people would have to choose good types of wood to avoid warping and termites, which meant increased costs. This problem can be completely solved if using steel purlins.
• Steel purlins reduce the number of wooden purlins, thereby limiting indiscriminate exploitation and deforestation, contributing to environmental protection.

2.2.2 Classification of steel purlins

Steel purlins are classified by shape. There are 3 types of steel purlin designs commonly used today as follows:

- C steel purlin

Steel C purlins, or simply called C purlins, are horizontal C-shaped steel bars used to bear the load from the roof deck or sheathing. This purlin's flat surface on one side has made it a popular material for cladding due to its ease of installation on concrete or steel structures. This type is light in weight and perfect for constructing simple spans.

C purlins are often used in large-scale construction projects such as gymnasiums, hospitals, warehouses, factories... with column steps less than 6m.

Common specifications for C steel purlins:

• C200x50x20x1.8: C purlin has a height of 200mm, wing width 50mm, whisker length 20mm and thickness 1.8mm;
• C150x50x20x1.5: C purlin has a height of 150mm, wing width 50mm, whisker length 20mm and thickness 1.5mm.

- Z steel purlin

A type of purlin with a Z-shaped cross-section, (has many advantages similar to C purlins such as: light, easy to process, transport, good bearing capacity, high durability, many sizes suitable for many projects) . However, Z purlins have a greater bearing capacity than C purlins, because the shape of Z purlins allows overlap at the joint points.

Z purlins can have holes punched at both ends or sides to help connect the purlins with bolts easily, and can be used in projects with column pitch greater than 6m.

Common specifications for Z purlins:

• Z200x72x78x2.0: Z purlin has a height of 200mm, two wings are 72mm and 78mm wide, and a thickness of 2.0mm;

• Z200x62x68x1.8: Z purlin has a height of 200mm, two wings are 62mm and 68mm wide, and a thickness of 1.8mm.

- U-shaped purlin

Similar to the above two types, U-shaped purlins have the same shape as the letter U. The advantage of U-shaped purlins is that they are light and durable and can be easily punched and processed according to different project specifications. U-shaped purlins are most commonly used in projects requiring corrugated iron roofs and steel structure roofs.

- Box steel purlins

Box steel purlins are also commonly used, in smaller projects such as residential houses. Or ancillary items such as decks or covered porches. Using box steel purlins is easier and more convenient because box steel is available and widely sold on the market. Because the bar is hollow, the caps are welded to the two ends of the purlin. To keep moisture inside and prevent metal corrosion. 

Using box steel purlins helps investors save costs. Which still brings the same aesthetics as wooden purlins.

2.3. Process and standards for manufacturing steel purlins
2.3.1 Production process

Steel purlins are produced based on a high-tech and closed production line. The steps are in order as follows:

• Step 1: Check the parameters and details on the steel purlin technical drawing.
• Step 2: Prepare standard ingredients.
• Step 3: Put steel into roll.
• Step 4: Check and adjust the gall and punch.
• Step 5: Install the technical parameters on the drawing into the production machine.
• Step 6: Test the obtained product.
• Step 7: Synchronous production according to orders.
• Step 8: Check the quality of the finished product.
• Step 9: Pack and apply certification stamp.
• Step 10: Deliver goods to the ordering unit.

2.3.2 Current standards for steel purlin production

There are 2 standards that need to be met when producing steel purlins today, including:

• Raw material standards G3302/BS 1397/SGH450. This is a standard established by the Japanese Industrial Standards Committee and published by the Japanese standards association.
• Quality standard ISO 9001:2015. Is the latest standard of ISO 9001 standard. Shows that steel purlin products have met quality and commercial requirements.

3. Steps to install roof purlins

If you understand what purlins are, readers should also learn the steps to erect roof purlins. To apply or monitor the construction process of your home project. There are 4 steps to install roof purlins as follows: 

• Step 1: Measure the tape from end to end along the roof rafters. To determine the number of purlins that will be needed for installation. Measure the width and height of the roof and record the measurements.
• Step 2: Dot a line of chalk horizontally across the roof from top to bottom. Place the first bar on the roof down along the chalk line starting at the two corners. Fasten purlins with nails to each vertical rafter. Insert two nails evenly spaced into the rafter.
• Step 3: Place the second purlin horizontally right next to the first purlin and install in the same way. Continue down the row until the first row is gone.
• Step 4: Move your legs down to the roof and draw a horizontal chalk line. Install the second row of purlins like the first row, cutting the end to fit. Dot the third chalk line down two more legs and continue down to the roof. Until it is completely covered with purlins. Check to make sure all nails are in place. And all the purlins were securely attached to the rafters.

4. What to keep in mind when constructing and designing roof purlins?

• When designing purlins, pay attention to roof weight: If the roofing sheet is heavy, use more purlins. Lighter roofing sheets are used less to save costs
• Purlins are balanced at a ratio of 1/32 between length and depth. Wood paneling and metal panels used for walls and roofs need to be suitable for the length and load of the roof purlins.
• The ideal distance between wall purlins and roof purlins is about 4-6 feet (equivalent to about 1.2-1.8m). The reason is because the roofing sheet will be used as a screen for tornadoes, rainstorms or earthquakes. The upside down bar part has the role of transferring gravity from the purlin to the support part to reduce pressure on the roof. 
• To increase horizontal stiffness and stability, roof top beams are used. The rods are fastened together at other points along their length.
• Choosing the type of purlin needs to consider the requirements of each type of project to use it properly.

So, above we have answered the question "what is a purlin". As well as basic information surrounding purlins. Through this, we hope readers understand the important role of purlins. As well as how to apply and install purlins in the most reasonable and cost-effective way.

Hung Nghiep Phu Construction Investment Co., Ltd. with the mission of bringing the best solutions and services, together with customers to build a prosperous community, Hung Nghiep Phu is gradually asserting its brand through Sincere cooperation, with a team of leaders with ethical capacity, creativity, dedication to the profession, and strategic vision. Hung Nghiep Phu owns a team of skilled and highly qualified staff who will bring customers the best quality projects. 

Hung Nghiep Phu Construction Investment Company Limited - specializes in constructing civil and industrial projects. We look forward to accompanying customers in construction projects as well as legal procedures such as planning diagrams, applying for construction permits, completing processes, applying for fire prevention and fighting certificates, ... If you have any questions or are in need of designing and perfecting the process, please contact us immediately for a free consultation!

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