Author:David Ran
Position:Senior Steel Structure Engineer at BF Steel Structure.
Introduction:With over 16 years of experience in steel structure design, fabrication, and project management, David has participated in more than 500 industrial steel building projects worldwide, including warehouses, workshops, agricultural buildings, and commercial steel structures.

What Are Purlins in Steel Structures?

Purlins in steel structures are secondary steel members used to support roof sheets, wall cladding and related building envelope materials. They are usually installed between the main steel frames, such as steel columns, roof beams and rafters, helping transfer loads from the roof or wall system to the main structural frame.

Although purlins are not as large as steel columns or main beams, they play an important role in steel structure buildings. In warehouses, workshops, factories and industrial plants, purlins affect roof stability, wall panel installation, building strength, material cost and on-site installation efficiency.

For customers planning a steel structure building project, understanding the basic function of purlins can help them communicate more clearly with the supplier and choose a more suitable building system.

What Are Purlins?

Purlins are horizontal structural members used in roof and wall systems. In steel structure buildings, they are commonly made from cold-formed steel sections, such as C-section purlins or Z-section purlins.

Roof purlins are installed on top of roof beams or rafters to support metal roof sheets, sandwich panels or insulation systems. Wall purlins, often called wall girts, are installed between steel columns to support wall cladding.

A complete steel structure building usually includes main steel frames, secondary steel components, roof and wall cladding, bolts, doors, windows, gutters, downpipes and accessories. Purlins belong to the secondary steel structure system, but they are essential for connecting the main frame with the roof and wall enclosure system.

Main Functions of Purlins in Steel Structures

1. Supporting Roof and Wall Cladding

The main function of purlins is to support roof sheets and wall panels. Without purlins, the roof and wall materials would not have enough support between the main steel frames.

In a steel warehouse or workshop, roof purlins carry the weight of roof sheets, insulation materials, skylight panels and other roof accessories. Wall purlins support wall cladding and help keep the wall system stable.

2. Transferring Loads to the Main Steel Frame

Purlins transfer roof and wall loads to the main steel frame. These loads may include the weight of cladding materials, wind load, snow load, maintenance load and other project-specific loads.

The purlin size and spacing must be designed according to the building span, local climate, roof material, wall material and engineering requirements.

3. Improving Roof and Wall Stability

Purlins help improve the stability of the roof and wall system. They provide support points for cladding materials and reduce the unsupported distance between roof sheets or wall panels.

A suitable purlin layout can help reduce deformation, improve wind resistance and make the roof and wall system more reliable for long-term use.

4. Helping with Fast Installation

Purlins are usually prefabricated and drilled in the factory before delivery. During installation, workers can connect them to the main steel frame with bolts or screws according to the drawings.

This helps improve construction efficiency and reduces on-site cutting or modification. For export steel structure projects, accurate purlin fabrication and clear component marking are very important.

5. Reducing Material Waste and Cost

Compared with using heavy steel members for every support point, cold-formed steel purlins provide an efficient and economical solution for roof and wall support.

The right purlin design can balance strength, weight, cost and installation convenience. This is why purlin spacing and section size should be designed by engineers instead of selected only by price.

Common Types of Purlins

C Purlins

C purlins are commonly used in steel structure buildings. They have a C-shaped cross section and are widely used for roof and wall support.

C purlins are often suitable for smaller spans, wall systems, roof support and general industrial building applications. They are easy to install and can be used with different roof and wall materials.

Z Purlins

Z purlins have a Z-shaped cross section and are often used in roof systems where overlapping connections are needed. Because of their shape, Z purlins can be lapped over supports, which helps improve continuity and strength in some building designs.

Z purlins are commonly used in larger steel structure buildings, warehouses, workshops and industrial plants.

Galvanized Purlins

Galvanized purlins are steel purlins with a zinc coating for improved corrosion resistance. They are often used in buildings where better anti-corrosion performance is required.

For humid environments, coastal areas or special industrial conditions, galvanized purlins may be a better choice than ordinary painted purlins.

Painted Purlins

Painted purlins are also widely used in steel structure buildings. They are usually treated with primer or anti-rust paint according to project requirements.

Painted purlins can be suitable for many standard warehouse, workshop and factory building projects, especially when the indoor environment is not highly corrosive.

Roof Purlins vs Wall Purlins

Roof purlins and wall purlins have different positions and functions.

Roof purlins are installed on the roof frame. They support roof sheets, sandwich panels, insulation layers, skylight panels and other roof materials. Their design must consider roof slope, drainage direction, wind load, snow load and roof maintenance load.

Wall purlins are installed between steel columns on the wall side. They support wall cladding and help form the building envelope. In many projects, wall purlins are also called wall girts.

For a complete steel structure building, roof purlins and wall purlins should be designed together with the main frame, cladding system, door openings, window layout and ventilation requirements.

Where Are Purlins Used?

Purlins are widely used in many steel structure building projects, including:

• Steel warehouse buildings
• Steel workshop buildings
• Steel structure factory buildings
• Industrial steel buildings
• Prefabricated steel buildings
• Agricultural steel buildings
• Storage sheds
• Logistics buildings
• Manufacturing plants
• Processing facilities

In warehouse buildings, purlins support large roof areas and wall panels. In workshop buildings, they help create a stable enclosure system for production and maintenance spaces. In factory buildings, purlins work with roof beams, columns and cladding to form a practical building system for long-term industrial use.

How Purlin Design Affects a Steel Building

Purlin design affects both building performance and project cost. If the purlin spacing is too large, the roof or wall sheets may not have enough support. If the purlins are too heavy or too closely spaced, the building cost may increase unnecessarily.

Important purlin design factors include:

• Building length and width
• Roof slope
• Main frame spacing
• Purlin spacing
• Roof and wall material type
• Wind load
• Snow load
• Seismic requirements
• Insulation requirements
• Skylight panel layout
• Door and window openings
• Local installation conditions

For overseas steel structure projects, purlins should also be designed with transportation and installation in mind. Proper hole positions, component marking and packing can make on-site installation easier.

Purlins and Roof Materials

Purlins must match the selected roof and wall materials. Common roof and wall materials include color steel sheets, EPS sandwich panels, PU sandwich panels and rock wool sandwich panels.

Different materials may require different purlin spacing and connection methods. For example, insulated sandwich panels may have different support requirements from single-layer metal sheets. Skylight panels, ventilation openings and roof accessories should also be considered during the design stage.

This is why customers should confirm roof and wall material requirements before finalizing the steel structure design.

Purlin Fabrication and Delivery

Purlins are usually produced by cold forming. After production, they can be cut to the required length, punched or drilled according to the connection details, treated with painting or galvanizing, and then packed for delivery.

For export projects, purlins should be clearly marked according to the installation drawings. Good packing helps protect the components during transportation and makes it easier for the construction team to identify each part on site.

At Bingfa Steel, purlins are supplied as part of the complete steel structure building package, together with the main steel frame, bracing system, roof and wall cladding, bolts and accessories.

What Information Is Needed for Quotation?

If you need a quotation for a steel structure building, purlin design will depend on the full building requirements. It is helpful to provide the following information:

• Building size: length, width and eave height
• Project location
• Building use
• Roof and wall material preference
• Wind load, snow load and seismic data
• Main frame spacing
• Door and window layout
• Insulation requirement
• Ventilation or skylight requirement
• Crane requirement, if any
• Installation support requirement

If you do not have complete technical information, you can first send the building size, project location and application. Our team can help discuss a suitable steel structure building solution.

Why Purlins Matter in Steel Structure Buildings

Purlins may look like small secondary components, but they are important for the performance of a steel structure building. They support the roof and wall system, transfer loads, improve stability and help make installation more efficient.

A good steel structure supplier should not only provide main steel columns and beams. The complete system should also include suitable purlins, bracing, wall girts, cladding, bolts and accessories according to the project design.

Bingfa Steel provides customized steel structure building solutions for warehouses, workshops, factories and industrial buildings. We can support customers with steel design communication, factory fabrication, export packing, container loading and installation guidance.

Steel is widely used in industrial buildings because it provides reliable strength, flexible design and long-term durability. For more information about global steel industry resources, you can refer to the World Steel Association.

For more technical background on structural steel design and steel building standards, you can also refer to the American Institute of Steel Construction.

FAQ

1. What are purlins in steel structures?

Purlins are secondary steel members used to support roof sheets, wall panels and other cladding materials in steel structure buildings.

2. What is the difference between C purlins and Z purlins?

C purlins have a C-shaped section and are widely used for roof and wall support. Z purlins have a Z-shaped section and are often used where overlapping connections and better continuity are required.

3. Are purlins part of the main steel frame?

Purlins are usually considered secondary steel components. The main steel frame includes columns, beams and rafters, while purlins support the roof and wall enclosure system.

4. Can purlin spacing be customized?

Yes. Purlin spacing should be designed according to roof material, wall material, main frame spacing, wind load, snow load and building requirements.

5. Are galvanized purlins better than painted purlins?

It depends on the project environment. Galvanized purlins usually provide better corrosion resistance, while painted purlins can be suitable for many standard industrial building projects.

Get a Custom Steel Structure Building Quote

If you need a custom steel structure building for a warehouse, workshop, factory or industrial project, contact Bingfa Steel for a customized solution. Send us your building size, project location, application, roof and wall material requirements, and our team will help you prepare a suitable design and quotation.

FAQ

① What is a steel structure building?

A steel structure building is a construction made primarily from high-strength steel components such as H-beams and columns. It is widely used for warehouses, workshops, poultry farms, and industrial facilities due to its durability and cost efficiency.

②How much does a steel building cost?

The cost of a steel building typically ranges from $30 to $80 per square meter depending on size, design, materials, and project location. Customized solutions may vary based on specific requirements.

③How long does it take to build a steel structure?

Production usually takes 20–40 days, while installation time depends on the project size. Most standard steel buildings can be installed within a few weeks.

④Do you provide installation support?

Yes, BINGFA Steel Structure provides detailed installation drawings and online guidance. We can also send engineers to your site if required.

⑤Can steel buildings withstand extreme weather?

Steel structures are designed to resist strong wind, heavy snow, and earthquakes. We customize designs based on local climate conditions.